JP5948698B2 - Ultraviolet light emitting device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an ultraviolet light emitting device and a method for manufacturing the same.

  Nitride semiconductor light-emitting elements that emit light in the visible to ultraviolet wavelength range are expected to be applied in various fields such as hygiene, medical, industrial, lighting, and precision machinery because of their low power consumption and small size. It has already been put into practical use in some wavelength regions such as the blue light wavelength region.

  However, nitride semiconductor light emitting devices are not limited to nitride semiconductor light emitting devices that emit blue light (hereinafter referred to as blue light emitting devices), and further improvements in light emission efficiency and light output are desired. In particular, nitride semiconductor light-emitting elements that emit light in the ultraviolet wavelength region (hereinafter referred to as ultraviolet light-emitting elements) are currently in practical use due to their significantly lower external quantum efficiency and light output than blue light-emitting elements. It has become a big barrier to. One of the causes is that the light emitting layer has low light emission efficiency (hereinafter referred to as internal quantum efficiency).

  The internal quantum efficiency of the light emitting layer formed of the nitride semiconductor crystal is affected by threading dislocations. Here, when the dislocation density of threading dislocations is high, non-radiative recombination becomes dominant, which causes a decrease in internal quantum efficiency.

  On the other hand, with respect to the deep ultraviolet light emitting device that emits light in the ultraviolet wavelength region of 230 nm to 350 nm, a light emitting efficiency improved by providing an AlN high quality buffer growth structure on a sapphire (0001) substrate has been proposed. (Patent Document 1).

  The AlN high-quality buffer growth structure described above has an AlN nucleation layer, a pulse supply AlN layer, and a continuously grown AlN layer, which are sequentially formed on a sapphire (0001) substrate.

The AlN nucleation layer, the pulse supply AlN layer, and the continuously grown AlN layer are formed by an MOCVD apparatus. The AlN nucleation layer is grown in the initial nucleation mode which is the first growth mode using the NH ₃ pulse supply method, and the pulse supply AlN layer is the slow growth which is the second growth mode using the NH ₃ pulse supply method. The continuous growth AlN layer is grown in a high-speed longitudinal growth mode. Here, Patent Document 1 describes that the second growth mode is a mode in which the grain size is expanded and the dislocation is reduced, and an AlN nucleation layer having unevenness can be embedded flatly. . Patent Document 1 describes that the high-speed vertical growth mode is a mode that further improves flatness and suppresses the generation of cracks, and does not use the AlN growth method based on the NH ₃ pulse supply method. Yes. The AlN growth method based on the NH ₃ pulse supply method is a method in which TMAl as an Al source is continuously supplied and NH ₃ as an N source is supplied in a pulse shape.

  In Patent Document 1, the growth temperatures of the AlN nucleation layer, the pulse supply AlN layer, and the continuously grown AlN layer are 1300 ° C., 1200 ° C., and 1200 ° C., respectively.

JP 2009-54780 A

  The above threading dislocations are particularly likely to occur at the growth interface when a substrate made of a material such as sapphire having a large lattice mismatch with respect to the nitride semiconductor is used as a single crystal substrate for epitaxial growth. Therefore, in order to obtain a nitride semiconductor crystal layer having a low threading dislocation density, it is a very important factor to control the behavior of each constituent element at the initial stage of growth.

  On the other hand, in the AlN high-quality buffer growth structure of the deep ultraviolet light-emitting device described in Patent Document 1, a large number of AlN nuclei are formed on a sapphire (0001) substrate in the early stage of growth. Here, threading dislocations are likely to occur at the boundary when adjacent AlN nuclei are bonded.

However, in the AlN high-quality buffer growth structure provided with the AlN nucleation layer described above, when the AlN nucleation layer is grown, the Al diffusion length is short, and AlN nuclei are generated at a high density in the initial stage of growth. Further, in Patent Document 1, an MOCVD apparatus is used as a manufacturing apparatus of a deep ultraviolet light emitting element, trimethylaluminum (TMAl) is used as an Al source gas, and ammonia (NH ₃ ) is used as an N source gas. In the above-described deep ultraviolet light-emitting device, during the production, when an AlN nucleation layer is grown, TMAl which is a general Al source gas and NH ₃ which is a general N source gas are in a gas phase. It is estimated that nanometer-order particles (nanoparticles) are formed by reaction. For this reason, in the above-described deep ultraviolet light-emitting device, when the AlN nucleation layer is grown, it is presumed that the nanoparticles exist on the surface of the single crystal substrate and inhibit the growth of the AlN crystal. Therefore, when manufacturing an ultraviolet light emitting device that must contain Al as a constituent element of the nitride semiconductor crystal, the nitride semiconductor crystal is compared with a blue light emitting device that does not contain Al as a constituent element of the nitride semiconductor crystal. Since many threading dislocations existed in the inside, the luminous efficiency was low.

  This invention is made | formed in view of the said reason, The objective is to provide the ultraviolet light emitting element which can reduce a threading dislocation, and its manufacturing method.

The ultraviolet light emitting device of the present invention includes a single crystal substrate, and a plurality of island-like nuclei formed on one surface of the single crystal substrate and made of Al _x Ga _1-x N (0 <x <1). A buffer layer made of Al _y Ga _1-y N (0 <y ≦ 1) formed on the one surface side of the single crystal substrate so as to fill the gaps between the nuclei and cover all the nuclei; An n _-type nitride semiconductor layer made of n-type Al _z Ga _{1 -zN} (0 <z ≦ 1) formed on the buffer layer, and the n-type nitride semiconductor layer opposite to the buffer layer side A light emitting layer having a quantum well structure having a well layer made of Al _a Ga _1-a N (0 <a ≦ 1) and formed on the side opposite to the n-type nitride semiconductor layer side in the light emitting layer and a p-type nitride semiconductor layer, wherein x <y.

  In this ultraviolet light emitting element, y = 1 is preferable.

  In this ultraviolet light emitting element, it is preferable that a <x.

  In this ultraviolet light emitting element, it is preferable that z <x.

  In this ultraviolet light emitting element, it is preferable that x, which is an Al composition, increases as the nucleus moves away from the single crystal substrate.

  In this ultraviolet light emitting device, the single crystal substrate is preferably a c-plane sapphire substrate.

The method for manufacturing an ultraviolet light-emitting device according to the present invention is a method for manufacturing the ultraviolet light-emitting device, wherein after the single crystal substrate is prepared and placed in a reaction furnace, a plurality of surfaces are formed on the one surface of the single crystal substrate. A first step of forming the nucleus; a second step of forming the buffer layer; a third step of forming the n-type nitride semiconductor layer; a fourth step of forming the light emitting layer; and the p-type. A fifth step of forming a nitride semiconductor layer, wherein the first step includes an Al source gas, a Ga source gas, and an N source in the reactor under a first substrate temperature and a first growth pressure. By supplying gas at a predetermined molar ratio, crystal nuclei composed of a plurality of Al _b Ga _1-b N (0 <b <1 and b <x) are formed on the one surface of the single crystal substrate. From the first step to be formed and Al _b Ga _1-b N (0 <b <1 and b <x) And a second step of desorbing Ga so that the crystal nucleus is the nucleus composed of Al _x Ga _1-x N (0 <x <1).

In the method of manufacturing an ultraviolet light emitting element, in the second step, the source gas of N is supplied without supplying the source gas of Al and the source gas of Ga, and at the temperature of the single crystal substrate. It is preferable to perform the heat treatment in a state where a certain substrate temperature is set higher than the first substrate temperature in the first step.

In the method of manufacturing an ultraviolet light emitting element, in the second step, the source gas of N is supplied without supplying the source gas of Al and the source gas of Ga, and at the temperature of the single crystal substrate. A carrier gas for transporting the raw material gas in the first step without changing a certain substrate temperature to be lower than the first substrate temperature in the first step. It is preferable to perform the heat treatment in a state where the amount of hydrogen gas is set to be larger than the supply amount.

In the ultraviolet light emitting device of the present invention, a plurality of island-shaped nuclei made of Al _x Ga _1-x N (0 <x <1) formed on one surface of a single crystal substrate and the adjacent nuclei A buffer layer made of Al _y Ga _1-y N (0 <y ≦ 1) formed on the one surface side of the single crystal substrate so as to fill the gap and cover all the nuclei, and x <y Therefore, there is an effect that threading dislocations can be reduced.

The method for manufacturing an ultraviolet light emitting device of the present invention includes a first step of forming a plurality of the nuclei on the one surface of the single crystal substrate, and a second step of forming the buffer layer. The process includes a first step of forming a crystal nucleus composed of a plurality of Al _b Ga _1-b N (0 <b <1 and b <x) on the one surface of the single crystal substrate, and Al _b Ga Ga is desorbed so that the crystal nucleus composed of _1-b N (0 <b <1 and b <x) becomes the nucleus composed of Al _x Ga _1-x N (0 <x <1). Since the second step is provided, it is possible to provide an ultraviolet light emitting element capable of reducing threading dislocations.

1 is a schematic cross-sectional view of an ultraviolet light emitting element according to Embodiment 1. FIG. 6 is a schematic cross-sectional view of an ultraviolet light-emitting element according to Embodiment 2. FIG.

(Embodiment 1)
Below, the ultraviolet light emitting element of this embodiment is demonstrated based on FIG.

The ultraviolet light emitting element fills the gap between the single crystal substrate 1, the plurality of island-like nuclei 2 formed on one surface of the single crystal substrate 1, and the adjacent nuclei 2 and covers all the nuclei 2. And the buffer layer 3 formed on the one surface side of the single crystal substrate 1. Here, in the ultraviolet light emitting element, the nucleus 2 is made of Al _x Ga _1-x N (0 <x <1), and the buffer layer 3 is made of Al _y Ga _1-y N (0 <y ≦ 1). , X <y.

Further, the ultraviolet light emitting element includes an n _-type nitride semiconductor layer 4 made of n-type Al _z Ga _1-z N (0 <z ≦ 1) formed on the buffer layer 3, and an n-type nitride semiconductor layer 4. The light emitting layer 5 of the quantum well structure formed in the opposite side to the buffer layer 3 side is provided. Here, in the ultraviolet light emitting element, the n-type nitride semiconductor layer 4 is made of n-type Al _z Ga _{1 -z} N (0 <z ≦ 1). In the ultraviolet light emitting element, the well layer 5b having a quantum well structure is made of Al _a Ga _1-a N (0 <a ≦ 1).

  Further, the ultraviolet light emitting element includes a p-type nitride semiconductor layer 7 formed on the light emitting layer 5 on the side opposite to the n-type nitride semiconductor layer 4 side.

  Further, the ultraviolet light emitting device includes a first electrode 14 electrically connected to the n-type nitride semiconductor layer 4 and a second electrode 17 electrically connected to the p-type nitride semiconductor layer 7. .

In the ultraviolet light emitting device, the p-type contact layer 8 is provided on the opposite side of the p-type nitride semiconductor layer 7 to the light-emitting layer 5 side, and the second electrode 17 is formed on a part of the p-type contact layer 8. It is preferable to do. In short, in the ultraviolet light emitting element, it is preferable that the second electrode 17 is electrically connected to the p-type nitride semiconductor layer 7 through the p-type contact layer 8. Here, in the ultraviolet light emitting element, it is preferable to provide the electron blocking layer 6 between the light emitting layer 5 and the p-type nitride semiconductor layer 7.

  The ultraviolet light emitting element has a mesa structure, and the first electrode 14 is formed on a part of the surface 4 a exposed on the light emitting layer 5 side in the n-type nitride semiconductor layer 4.

Further, in the ultraviolet light emitting element, the well layer 5b of the light emitting layer 5 is made of Al _a Ga _1-a N (0 <a ≦ 1) as described above, and the emission wavelength (emission peak wavelength) is in the ultraviolet wavelength region of 210 nm to 360 nm. ).

  Hereinafter, each component of the ultraviolet light emitting element will be described in detail.

Single crystal substrate 1 is a substrate for epitaxial growth. The single crystal substrate 1 is preferably a sapphire substrate with one surface having a (0001) plane, that is, a c-plane sapphire substrate (α-Al ₂ O ₃ substrate). However, the c-plane sapphire substrate preferably has an off angle from (0001) of 0 to 0.2 °. This makes it possible to reduce the density of the nuclei 2 when forming the group of nuclei 2 on the one surface of the single crystal substrate 1 during the manufacture of the ultraviolet light emitting element, and to improve the quality of the buffer layer 3. Can be achieved. This is because atoms supplied to form the nucleus 2 diffuse on the one surface of the single crystal substrate 1 and contribute to crystal growth at a stable location, and the off-angle of the single crystal substrate 1 is smaller. This is because the terrace width is long and the density of the nuclei 2 is easily reduced. The single crystal substrate 1 is not limited to the c-plane sapphire substrate, and may be a gallium oxide substrate such as a β-Ga ₂ O ₃ substrate, for example.

The plurality of island-like nuclei 2 are provided to reduce threading dislocations generated in the n-type nitride semiconductor layer 4 due to a difference in lattice constant between the single crystal substrate 1 and the n-type nitride semiconductor layer 4 . Is. In the ultraviolet light emitting device of this embodiment, the height dimension of the nucleus 2 is set to about 10 nm, but it is not particularly limited to this value. If the height dimension of the nucleus 2 is too large, cracks will occur in the buffer layer 3 due to the lattice constant, and if it is too small, the function as a growth nucleus for forming the buffer layer 3 may not be exhibited. is there. For this reason, the height dimension of the nucleus 2 is preferably set, for example, in the range of about 0.5 nm to 50 nm, and more preferably set in the range of about 1 nm to 25 nm. In short, the nucleus 2 is preferably a microcrystal having a height dimension of about 0.5 nm to 50 nm, and more preferably a microcrystal having a height dimension of about 1 nm to 25 nm. Further, it is preferable that the plurality of island-like nuclei 2 have a small variation in height dimension.

The nucleus 2 is made of Al _x Ga _1-x N (0 <x <1). Here, the composition ratio of _{Al x Ga 1-x N (} 0 <x <1) is not particularly limited, the band gap energy of the _{Al x Ga 1-x N (} 0 <x <1) is, It is preferably set so as to be higher than the band gap energy of each of n-type nitride semiconductor layer 4 and well layer 5b. For example, when z which is the Al composition of the n-type nitride semiconductor layer 4 is 0.65 and a which is the Al composition of the well layer 5b is 0.5, Al _x Ga _1-x N (0 <x < X which is the composition of Al in 1) is preferably set in the range of 0.66 to 0.99. Here, the nucleus 2 is made of Al _0.66 Ga _0.34 N when x is 0.66, and made of Al _0.99 Ga _0.01 N when x is 0.99. In the ultraviolet light-emitting device of this embodiment, as an example, _x , which is the Al composition of Al _x Ga _1-x N (0 <x <1), is set to 0.8. That is, in the example of the ultraviolet light emitting element of this embodiment, the nucleus 2 is composed of Al _0.8 Ga _0.2 N. In Al _x Ga _1-x N (0 <x <1), 1-x, which is a composition of Ga, may be less than 0.01. That is, the nucleus 2 may be AlN doped with Ga during the growth of the nucleus 2.

  The buffer layer 3 is provided for the purpose of reducing threading dislocations. If the film thickness is too thin, the reduction of threading dislocations tends to be insufficient, and if the film thickness is too thick, cracks caused by lattice mismatching are likely to occur. There is a concern that the generation and the warpage of the wafer forming a plurality of ultraviolet light emitting elements may increase. For this reason, the film thickness of the buffer layer 3 is preferably set in the range of about 500 nm to 10 μm, and more preferably set in the range of 1 μm to 5 μm. The film thickness of the buffer layer 3 is preferably set so that the surface of the buffer layer 3 is flattened. In the ultraviolet light emitting device of this embodiment, as an example, the film thickness of the buffer layer 3 is set to 3 μm, but this is an example and is not particularly limited.

The buffer layer 3 is made of Al _y Ga _1-y N (0 <y ≦ 1), and it is sufficient that x <y. In the ultraviolet light emitting device of this embodiment, as an example, _y , which is the Al composition of Al _y Ga _1-y N (0 <y ≦ 1), is set to 1. That is, in the example of the ultraviolet light emitting element of this embodiment, the buffer layer 3 is made of AlN.

The n-type nitride semiconductor layer 4 is for transporting electrons to the light emitting layer 5. The thickness of the n-type nitride semiconductor layer 4 is set to 2 μm as an example, but the thickness is not particularly limited. The n-type nitride semiconductor layer 4 is made of n-type Al _z Ga _{1 -zN} (0 <z ≦ 1). Here, the composition ratio of n-type Al _z Ga _1-z N (0 <z ≦ 1) constituting the n-type nitride semiconductor layer 4 is a composition ratio that does not absorb ultraviolet light emitted from the light emitting layer 5. There is no particular limitation. For example, in the case where the Al composition of the well layer 5b in the light emitting layer 5 is 0.5 and the Al composition of the barrier layer 5a is 0.65, n-type Al _z Ga _{1 -z} N (0 <z ≦ 1) X) which is the Al composition of () can be 0.65 which is the same as the Al composition of the barrier layer 5a. That is, when the well layer 5b of the light emitting layer 5 is made of Al _0.5 Ga _0.5 N and the barrier layer 5a is made of Al _0.65 Ga _0.35 N, the n-type nitride semiconductor layer 4 is, for example, n-type Al _0.65 Ga _0.35 N can do. In the ultraviolet light emitting device of this embodiment, as an example, the thickness of the n-type nitride semiconductor layer 4 is set to 2 μm, but the thickness is not limited to this. In addition, as a donor impurity of the n-type nitride semiconductor layer 4, Si is preferable, for example. Further, the electron concentration of the n-type nitride semiconductor layer 4 may be set, for example, in the range of about 1 × 10 ¹⁸ to 1 × 10 ¹⁹ cm ⁻³ . In the present embodiment, as an example, the electron concentration of the n-type nitride semiconductor layer 4 is set to 8 × 10 ¹⁸ cm ⁻³ .

  The light-emitting layer 5 converts injected carriers (here, electrons and holes) into light, and has a quantum well structure. The quantum well structure includes a barrier layer 5a and a well layer 5b. In the example shown in FIG. 1, the barrier layers 5a and the well layers 5b are alternately stacked, and the number of the well layers 5b is 2. However, the number of the well layers 5b is not particularly limited. In short, the quantum well structure may be a multiple quantum well structure or a single quantum well structure. Further, the film thicknesses of the well layer 5b and the barrier layer 5a are not particularly limited. However, in the light emitting layer 5, when the well layer 5b is too thick, electrons and holes injected into the well layer 5b are spatially caused by a piezo electric field due to lattice mismatch in the quantum well structure. As a result, the light emission efficiency decreases. Further, in the light emitting layer 5, when the film thickness of the well layer 5b is too thin, the carrier confinement effect is lowered and the light emission efficiency is lowered. For this reason, the thickness of the well layer 5b is preferably about 1 nm to 5 nm, and more preferably about 1.3 nm to 3 nm. Moreover, it is preferable to set the film thickness of the barrier layer 5a in the range of about 5 nm to 15 nm, for example. In the present embodiment, as an example, the thickness of the well layer 5b is set to 2 nm and the thickness of the barrier layer 5a is set to 10 nm. However, the thickness is not limited to these.

In the light emitting layer 5, the Al composition of the well layer 5b is set so as to emit ultraviolet light having a desired emission wavelength. Here, the light emitting layer 5 including the well layer 5b made of Al _a Ga _1-a N (0 <a ≦ 1) has an emission wavelength of 210 nm by changing a which is the Al composition of the well layer 5b. It is possible to set an arbitrary emission wavelength in a range of ˜360 nm. For example, when the desired emission wavelength is around 265 nm, a that is the Al composition may be set to 0.50.

The electron blocking layer 6 suppresses leakage (overflow) of electrons injected into the light emitting layer 5 that have not recombined with holes in the light emitting layer 5 to the p-type nitride semiconductor layer 7 side. Therefore, it is provided between the light emitting layer 5 and the p-type nitride semiconductor layer 7. The electron block layer 6 is made of p-type Al _c Ga _1-c N (0 <c <1). Here, the composition ratio of the p-type Al _c Ga _1-c N (0 <c <1) is not particularly limited, but the band gap energy of the electron blocking layer 6 may be p-type nitride semiconductor layer 7 or It is preferable to set so as to be higher than the band gap energy of the barrier layer 5a. Further, the hole concentration of the electron blocking layer 6 is not particularly limited. Further, the film thickness of the electron blocking layer 6 is not particularly limited, but if the film thickness is too thin, the overflow suppressing effect is reduced, and if the film thickness is too thick, the resistance of the ultraviolet light emitting element is increased. Here, the film thickness of the electron blocking layer 6 varies depending on values such as c, which is the composition of Al, and the hole concentration. Therefore, although it cannot be generally stated, it is set within a range of 1 nm to 50 nm. It is preferable to set within a range of 5 nm to 25 nm.

The p-type nitride semiconductor layer 7 is for transporting holes to the light emitting layer 5. The p-type nitride semiconductor layer is made of p-type Al _d Ga _1-d N (0 <d <1). Here, the composition ratio of p-type Al _d Ga _1-d N (0 <d <1) is not particularly limited as long as it is a composition ratio that does not absorb ultraviolet light emitted from the light emitting layer 5. For example, when the Al composition of the well layer 5b in the light emitting layer 5 is 0.5 and the Al composition of the barrier layer 5a is 0.65 as described above, p-type Al _d Ga _1-d N (0 <d < For example, d, which is the Al composition of 1), can be set to 0.65, which is the same as a which is the Al composition of the barrier layer 5a. That is, when the well layer 5b of the light emitting layer 5 is made of Al _0.5 Ga _0.5 N, the p-type nitride semiconductor layer 7 can be composed of, for example, p-type Al _0.65 Ga _0.35 N. As the acceptor impurity of the p-type nitride semiconductor layer 7, Mg is preferable.

Further, the hole concentration of the p-type nitride semiconductor layer 7 is not particularly limited, and a higher concentration is preferable in the hole concentration range in which the film quality of the p-type nitride semiconductor layer 7 does not deteriorate. However, since the hole concentration of p-type Al _d Ga _1-d N (0 <d <1) is lower than the electron concentration of n-type Al _z Ga _1-z N (0 <z ≦ 1), p-type nitriding When the film thickness of the physical semiconductor layer 7 is too thick, the resistance of the ultraviolet light emitting element becomes too large. For this reason, the film thickness of the p-type nitride semiconductor layer 7 is preferably 200 nm or less, and more preferably 100 nm or less. In the ultraviolet light emitting device of this embodiment, as an example, the thickness of the p-type nitride semiconductor layer 7 is set to 20 nm.

The p-type contact layer 8 is provided in order to reduce the contact resistance with the second electrode 17 and obtain good ohmic contact with the second electrode 17. The p-type contact layer 8 is made of p-type GaN. Here, the hole concentration of the p-type GaN constituting the p-type contact layer 8 is preferably higher than that of the p-type nitride semiconductor layer 7, for example, about 7 × 10 ¹⁷ cm ^−3. Thus, it is possible to obtain good electrical contact with the second electrode 17. However, the hole concentration of p-type GaN is not particularly limited, and may be changed as appropriate within the range of the hole concentration at which good electrical contact with the second electrode 17 is obtained. The film thickness of the p-type contact layer 8 is set to 100 nm, but is not limited thereto, and may be set, for example, in the range of 50 nm to 150 nm.

  The first electrode 14, which is an n-electrode, is a laminate in which a Ti film with a thickness of 20 nm, an Al film with a thickness of 100 nm, a Ti film with a thickness of 20 nm, and an Au film with a thickness of 200 nm are stacked. It is formed by annealing after forming the film. The structure and film thickness of this laminated film are not particularly limited. In the ultraviolet light emitting element, a first pad (not shown) made of, for example, an Au film is formed on the first electrode 14. The first pad is formed after the first electrode 14 is formed. Note that the first pad 14 may also serve as the first pad without forming the first pad separately from the first electrode 14.

  The second electrode 17 which is a p-electrode is formed by forming a laminated film of a Ni film having a thickness of 15 nm and an Au film having a thickness of 100 nm and then performing an annealing process. The structure and film thickness of this laminated film are not particularly limited. In the ultraviolet light emitting element, a second pad (not shown) made of, for example, an Au film is formed on the second electrode 17. The second pad is formed after the second electrode 17 is formed.

  Hereinafter, the manufacturing method of the ultraviolet light emitting element of this embodiment is demonstrated.

(1) Step of introducing the single crystal substrate 1 into the reaction furnace In this step, the single crystal substrate 1 made of, for example, a c-plane sapphire substrate is introduced into the reaction furnace of the MOCVD apparatus. In this step, it is preferable to clean the surface of the single crystal substrate 1 by performing pretreatment with chemicals on the single crystal substrate 1 before introducing the single crystal substrate 1 into the reaction furnace. Also, in this step, after introducing the single crystal substrate 1 into the reaction furnace, the inside of the reaction furnace is evacuated, and then the purified furnace is made to flow through the reaction furnace by flowing highly purified nitrogen gas or the like into the reaction furnace. The gas may be exhausted after being filled with nitrogen gas. As a result, in this step, it is possible to exhaust a gas such as air that is unintentionally mixed when the single crystal substrate 1 is introduced. Single crystal substrate 1 is preferably in a wafer state in which a plurality of ultraviolet light emitting elements can be formed.

(2) Step of heating the single crystal substrate 1 to clean the one surface of the single crystal substrate 1 In this step, the substrate temperature, which is the temperature of the single crystal substrate 1 introduced into the reaction furnace, is defined as a first regulation. The temperature is raised to a temperature, and further, the one surface of the single crystal substrate 1 is cleaned by heating at the first specified temperature. The first specified temperature is set to 1100 ° C.

More specifically, in this step, after reducing the pressure in the reaction furnace to the first specified pressure, the substrate temperature is raised to the first specified temperature while maintaining the first specified pressure in the reaction furnace. The one surface of the single crystal substrate 1 is cleaned by heating at the first specified temperature for a first specified time. In this step, cleaning can be effectively performed by heating the single crystal substrate 1 in a state where H ₂ gas is supplied into the reaction furnace.

  Here, the first specified pressure is set to 10 kPa≈76 Torr. The first specified temperature is preferably set in a temperature range of 1000 to 1150 ° C, and more preferably set in a temperature range of 1050 to 1100 ° C. When the substrate temperature is lower than 1000 ° C., it is difficult to obtain a cleaning effect. The first specified time is set to 10 minutes. The values of the first specified pressure and the first specified time are examples, and are not particularly limited.

(3) Step of forming a plurality of island-like nuclei 2 made of Al _x Ga _1-x N (0 <x <1) (first step)
In this step, while maintaining the substrate temperature at the second specified temperature, which is the same as the first specified temperature, while maintaining the pressure in the reactor at the second specified pressure, the Al source gas, the Ga source gas, By supplying N source gas, a plurality of island-like nuclei 2 are formed on the one surface of the single crystal substrate 1. That is, in this step, a group of nuclei 2 is formed.

More specifically, in this step, a plurality of island-like nuclei 2 made of Al _x Ga _1-x N (0 <x <1) can be grown at the substrate temperature which is the temperature of the single crystal substrate 1. 2nd specified temperature. As with the first specified temperature, the second specified temperature is preferably a temperature at which the one surface of the single crystal substrate 1 made of a c-plane sapphire substrate is not altered, and is preferably set within a temperature range of 1000 to 1150 ° C. It is more preferable to set within a temperature range of ˜1100 ° C. In this step, since the diffusion length of Ga on the one surface of the single crystal substrate 1 is longer than the diffusion length of Al, the group III constituent element in the nucleus 2 made of a group III-V nitride semiconductor is only Al. Compared to the above case, the density of the nuclei 2 formed on the one surface of the single crystal substrate 1 (the number of nuclei 2 per unit area) can be reduced. In this step, when the substrate temperature is lower than 1000 ° C., Al atoms are not sufficiently diffused and it is difficult to control the density of the nuclei 2 formed on the one surface of the single crystal substrate 1 (low It becomes difficult to increase the density). For this reason, at the time of growth in the second step, which will be described later, dislocations generated at the interface when two adjacent members are bonded to each other increase, and as a result, there is a high possibility that a high-quality buffer layer 3 cannot be obtained.

  In this step, the second specified pressure is 10 kPa which is the same as the first specified pressure, and the second specified temperature is 1100 ° C. which is the same as the first specified temperature. Note that the values of the second specified pressure and the second specified temperature are examples, and are not particularly limited.

In this step, the TMAl flow rate is 0.05 L / min (50 SCCM) in the standard state, the TMGa flow rate is 0.01 L / min (10 SCCM) in the standard state, and the NH ₃ flow rate is 0.05 L / min in the standard state. Each is set to min (50 SCCM). Here, as the carrier gas for TMAl, TMGa and NH ₃ , for example, it is preferable to employ H ₂ gas, for example. Note that the flow rates of TMAl, TMGa, and NH ₃ are merely examples, and are not particularly limited.

(4) Step of forming buffer layer 3 made of Al _y Ga _1-y N (0 <y ≦ 1) (second step)
In this step, a buffer composed of Al _y Ga _1-y N (0 <y ≦ 1) is supplied by supplying a group III constituent element source gas and a group V constituent element source gas after the first step. In this step, the layer 3 is formed. Here, for example, H ₂ gas is preferably used as the carrier gas of each source gas.

  In this step, the buffer layer 3 having a predetermined film thickness (for example, 3 μm) is formed based on the group of nuclei 2 formed on the one surface of the single crystal substrate 1. The buffer layer 3 is provided for the purpose of reducing the threading dislocation density.

In this step, for example, in the state where the substrate temperature is maintained at the third specified temperature (predetermined growth temperature) while maintaining the pressure in the reactor at the third specified pressure, Al _y Ga _1-y N (0 <y ≦ The supply of the group III source gas and the group V source gas of 1) into the reaction furnace is started, and the buffer layer 3 is formed. In this step, the third specified pressure is set to 10 kPa, which is the same as the first specified pressure, and the third specified temperature is set to 1200 ° C. Note that the values of the third specified pressure and the third specified temperature are examples, and are not particularly limited.

In this step, for example, when y, which is an Al composition of Al _y Ga _1-y N (0 <y ≦ 1), is set to 1, that is, when the buffer layer 3 is made of AlN, for example, a group III material TMAl as a gas and NH ₃ as a group V source gas are supplied into the reactor. In this case, for example, the flow rate of TMAl is set to 0.05 L / min (50 SCCM) in a standard state, and the flow rate of NH ₃ is set to 0.1 L / min (100 SCCM) in a standard state. TMAl and NH ₃ may be supplied into the reaction furnace.

Further, in this step, TMy and TMGa as group III source gases and group V source when y which is the Al composition of Al _y Ga _1-y N (0 <y ≦ 1) is less than 1 NH ₃ as a gas may be supplied into the reaction furnace. In this case, the molar ratio of TMAl in the group III source gas ([TMAl] / {[TMAl] + [TMGa]} so that y which is the composition of Al becomes a desired value (0 <y <1)). ) Etc. may be set.

(5) Step of forming n-type nitride semiconductor layer 4 (third step)
This step is a step of forming the n-type nitride semiconductor layer 4 on the buffer layer 3.

In this step, for example, the pressure in the reactor while holding the substrate temperature while keeping the fourth specified pressure to the fourth predetermined temperature (predetermined growth temperature), n-type _{Al z Ga 1-z N (} 0 < The supply of a group III source gas of z ≦ 1), a group V source gas, and an impurity source gas imparting n-type conductivity is started into the reaction furnace to form the n-type nitride semiconductor layer 4. In this step, the fourth specified pressure is 10 kPa, which is the same as the first specified pressure, and the fourth specified temperature is 1100 ° C. In addition, each value of 4th specified pressure and 4th specified temperature is an example, and it does not specifically limit it.

In this step, TMAl is used as the Al source gas, TMGa is used as the Ga source gas, NH _{3 is used} as the N source gas, and tetraethylsilane (TESi) is used as the Si source gas that imparts n-type conductivity. . Further, H ₂ gas is used as a carrier gas for transporting each source gas. Here, the flow rate of TESi is set to 0.0009 L / min (0.9 SCCM) in a standard state. Further, the molar ratio of TMAl in the group III source gas ([TMAl] / {[TMAl] + [TMGa]}) is set so that the Al composition becomes a desired value (for example, 0.65). . Each source gas is not particularly limited. For example, triethylgallium (TEGa) may be used as a Ga source material, hydrazine derivative may be used as a N source gas, and monosilane (SiH ₄ ) may be used as a Si source material. Moreover, the flow rate of each source gas is an example, and is not particularly limited.

(6) Step of forming the light emitting layer 5 (fourth step)
This step is a step of forming the light emitting layer 5 on the n-type nitride semiconductor layer 4.

  In this step, for example, with the substrate temperature maintained at the fifth specified temperature (predetermined growth temperature) while maintaining the pressure in the reactor at the fifth specified pressure, the group III source gas and the group V source gas are added. The supply into the reaction furnace is started to form the light emitting layer 5. In this step, the fifth specified pressure is 10 kPa, the same as the first specified pressure, and the fifth specified temperature is 1100 ° C. Note that the values of the fifth specified pressure and the fifth specified temperature are examples, and are not particularly limited.

In this step, as an example, the growth conditions of the well layer 5b and the barrier layer 5a are set so that the well layer 5b of the light emitting layer 5 becomes Al _0.5 Ga _0.5 N and the barrier layer 5a becomes Al _0.65 Ga _0.35 N. Yes. The composition ratio of each of the well layer 5b and the barrier layer 5a is not particularly limited. In this step, the well layer 5b and the barrier layer 5a are each based on the desired composition ratio of each of the well layer 5b and the barrier layer 5a. What is necessary is just to set the growth conditions.

In this step, TMAl is used as the Al source gas, TMGa is used as the Ga source gas, NH ₃ is used as the N source gas, and H ₂ gas is used as the carrier gas for transporting each source gas. Here, regarding the growth conditions of the well layer 5b of the light emitting layer 5, the molar ratio of TMAl in the group III source gas ([TMAl] / {[TMAl] + [TMGa]}) is obtained so as to obtain a desired composition ratio. ) Is set. In this step, the molar ratio under the growth condition of the well layer 5b is set smaller than the molar ratio under the growth condition of the barrier layer 5a. In the ultraviolet light emitting device of this embodiment, the barrier layer 5a is not doped with impurities. However, the present invention is not limited to this, and impurities such as Si may be doped at a concentration that does not deteriorate the crystal quality of the barrier layer 5a. Good. Here, as the Si source gas, for example, TESi can be used. Each source gas is not particularly limited. For example, TEGa may be used as a Ga source material, a hydrazine derivative may be used as an N source gas, and SiH ₄ may be used as an Si source material. Moreover, the flow rate of each source gas is an example, and is not particularly limited.

(7) Step of forming the electron block layer 6 This step is a step of forming the electron block layer 6 on the light emitting layer 5.

  In this step, for example, with the substrate temperature maintained at the sixth specified temperature (predetermined growth temperature) while maintaining the pressure in the reactor at the sixth specified pressure, the group III source gas and the group V source gas are added. The supply into the reaction furnace is started, and the electron block layer 6 is formed. In this step, the sixth specified pressure is 10 kPa, which is the same as the first specified pressure, and the sixth specified temperature is 1100 ° C. The values of the sixth specified pressure and the sixth specified temperature are merely examples, and are not particularly limited. The substrate temperature under the growth condition of the light emitting layer 5 and the substrate temperature under the growth condition of the electron block layer 6 are preferably the same temperature, but are not necessarily the same temperature.

In this step, TMAl is used as the Al source gas, TMGa is used as the Ga source gas, NH _{3 is used} as the N source gas, and biscyclopentadienyl magnesium (Cp ₂₎ is used as the Mg source gas that contributes to p-type conductivity. Mg) is used, and H ₂ gas is used as a carrier gas for transporting each source gas. Here, the molar ratio of TMAl in the group III source gas ([TMAl] / {[TMAl] + [TMGa]}) is set so that the Al composition becomes a desired value (for example, 0.9). Yes. Each source gas is not particularly limited. For example, TEGa may be used as a Ga source material, and a hydrazine derivative may be used as an N source gas. The flow rate of each source gas is an example and is not particularly limited.

(8) Step of forming p-type nitride semiconductor layer 7 (fifth step)
This step is a step of forming the p-type nitride semiconductor layer 7 on the electron block layer 6. In the case where the electron blocking layer 6 is not provided, the step of forming the p-type nitride semiconductor layer 7 on the light emitting layer 5 is performed.

  In this step, for example, with the substrate temperature maintained at the seventh specified temperature (predetermined growth temperature) while maintaining the pressure in the reactor at the seventh specified pressure, the group III source gas and the group V source gas are mixed. The supply into the reaction furnace is started, and the p-type nitride semiconductor layer 7 is formed. In this step, the seventh specified pressure is 10 kPa, which is the same as the first specified pressure, and the seventh specified temperature is 1100 ° C. Note that the values of the seventh specified pressure and the seventh specified temperature are examples, and are not particularly limited.

In this step, TMAl is used as the Al source gas, TMGa is used as the Ga source gas, NH _{3 is used} as the N source gas, and Cp ₂ Mg is used as the Mg source gas that imparts p-type conductivity. H ₂ gas is used as a carrier gas for transporting the gas. Here, the molar ratio of TMAl in the group III source gas ([TMAl] / {[TMAl] + [TMGa]}) is set so that the Al composition becomes a desired value (for example, 0.65). Yes. When the Al composition is the same as the Al composition in the n-type nitride semiconductor layer 4, the same molar ratio as the growth conditions of the n-type nitride semiconductor layer 4 can be set. The flow rate of each source gas is an example and is not particularly limited.

(9) Step of forming p-type contact layer 8 This step is a step of forming p-type contact layer 8 on p-type nitride semiconductor layer 7.

  In this step, for example, the group III source gas and the group V source gas are added while maintaining the substrate temperature at the eighth specified temperature (predetermined growth temperature) while maintaining the pressure in the reactor at the eighth specified pressure. Supply into the reaction furnace is started, and the p-type contact layer 8 is formed. In this step, the eighth specified pressure is 10 kPa, which is the same as the first specified pressure, and the eighth specified temperature is 1050 ° C. Note that the values of the eighth specified pressure and the eighth specified temperature are merely examples, and are not particularly limited.

In this step, TMGa is used as the Ga source gas, NH _{3 is used} as the N source gas, and Cp ₂ Mg is used as the Mg source gas that imparts p-type conductivity, and the carrier for transporting each source gas is used. H ₂ gas is used as the gas.

  After the single crystal substrate 1 is introduced into the reactor of the MOCVD apparatus in the step (1), crystal growth is continuously performed in the reactor of the MOCVD apparatus until the step (9) is completed. Then, after the growth of the p-type contact layer 8 is finished, the substrate temperature is lowered to near room temperature, the nucleus 2, the buffer layer 3, the n-type nitride semiconductor layer 4, the light emitting layer 5, the electron blocking layer 6, and the p-type nitriding. The single crystal substrate 1 on which the stacked structure of the physical semiconductor layer 7 and the p-type contact layer 8 is grown is taken out from the MOCVD apparatus. In short, in the manufacturing method of the ultraviolet light emitting device of this embodiment, the nucleus 2, the buffer layer 3, the n-type nitride semiconductor layer 4, the light emitting layer 5, the electron blocking layer 6, the p-type nitride semiconductor layer 7, and the p-type contact layer. 8 is formed by the MOCVD method.

(10) Step of performing annealing for activating p-type impurities In this step, the electron blocking layer 6 and the p-type nitriding are held in the annealing furnace of the annealing apparatus by holding at a predetermined annealing temperature for a predetermined annealing time. This is a step of activating p-type impurities in the physical semiconductor layer 7 and the p-type contact layer 8. Here, the annealing temperature is set to 750 ° C. and the annealing time is set to 10 minutes. However, these values are merely examples, and are not particularly limited. As the annealing apparatus, for example, a lamp annealing apparatus, an electric furnace annealing apparatus, or the like can be employed.

(11) Step of forming mesa structure First, in the stacked structure grown on the one surface side of the single crystal substrate 1 using a general photolithography technique, on the region corresponding to the upper surface of the mesa structure A first resist layer is formed. Subsequently, by using the first resist layer as a mask, the stacked structure is etched from the surface side (here, the surface side of the p-type contact layer 8) to the middle of the n-type nitride semiconductor layer 4, thereby forming a mesa structure. Form. Thereafter, the first resist layer is removed. Etching of the laminated structure can be performed by, for example, reactive ion etching. The area and shape of the mesa structure are not particularly limited.

(12) Step of forming the first electrode 14 on the exposed surface 4a of the n-type nitride semiconductor layer 4 Only the region where the first electrode 14 is to be formed on the one surface side of the single crystal substrate 1 (that is, the n-type) A second resist layer patterned so as to expose a part of the nitride semiconductor layer 4 with a reduced thickness) is formed. Thereafter, for example, a laminated film of a Ti film having a thickness of 20 nm, an Al film having a thickness of 100 nm, a Ti film having a thickness of 20 nm, and an Au film having a thickness of 200 nm is formed by electron beam evaporation, and lift-off is performed. By performing the step, the second resist layer and the unnecessary film on the second resist layer are removed. Thereafter, an RTA (Rapid Thermal Annealing) process is performed in an N ₂ gas atmosphere so that the contact between the first electrode 14 and the n-type nitride semiconductor layer 4 becomes an ohmic contact. The structure and each film thickness of the laminated film are examples, and are not particularly limited. The RTA treatment conditions may be, for example, an annealing temperature of 800 ° C. and an annealing time of 1 minute, but these values are merely examples and are not particularly limited.

(13) Step of Forming Second Electrode 17 Only the region where the second electrode 17 is to be formed on the one surface side of the single crystal substrate 1 (here, part of the surface of the p-type contact layer 8) is exposed. A patterned third resist layer is formed. Thereafter, for example, an Ni film having a thickness of 15 nm and an Au film having a thickness of 100 nm are formed by electron beam evaporation, and lift-off is performed, so that the third resist layer and the unnecessary film on the third resist layer are formed. Remove. Thereafter, an RTA treatment is performed in an N ₂ gas atmosphere so that the contact between the second electrode 17 and the p-type contact layer 8 is an ohmic contact. The structure and each film thickness of the laminated film are examples, and are not particularly limited. The RTA treatment conditions may be, for example, an annealing temperature of 400 ° C. and an annealing time of 15 minutes, but these values are merely examples and are not particularly limited.

(14) Step of Forming First Pad and Second Pad In this step, the first pad and the second pad are formed using photolithography technology and thin film formation technology. As the thin film formation technique, for example, an electron beam evaporation method or the like can be employed.

  By completing this step, a wafer on which a plurality of ultraviolet light emitting elements are formed is completed. In short, by sequentially performing the steps (1) to (14) described above, a wafer on which a plurality of ultraviolet light emitting elements are formed is completed.

(15) Process of Dividing from Wafer into Individual Ultraviolet Light Emitting Elements This process is a dicing process, and the wafer is cut into individual ultraviolet light emitting elements (chips) by cutting with a dicing saw or the like. Thereby, a plurality of ultraviolet light emitting elements can be obtained from one wafer. Examples of the chip size of the ultraviolet light emitting element include 350 μm □ and 1 mm □, but are not particularly limited.

  By the way, the above-mentioned 1st process is good also as a process provided with the 1st step and 2nd step which are demonstrated below.

The first step supplies Al source gas, Ga source gas, and N source gas in a predetermined molar ratio into the reaction furnace at a first substrate temperature and a first growth pressure (first specified pressure). This is a step of forming crystal nuclei composed of a plurality of Al _b Ga _1-b N (0 <b <1 and b <x) on the one surface of the single crystal substrate 1. In this first step, for example, the first substrate temperature may be set to 1100 ° C. and the first growth pressure may be set to 10 kPa. However, these numerical values are merely examples, and are not particularly limited.

In the second step, a crystal nucleus composed of Al _b Ga _1-b N (0 <b <1 and b <x) is used as a nucleus 2 composed of Al _x Ga _1-x N (0 <x <1). In this way, Ga is desorbed. In short, in the first process including the first step and the second step, by performing the first step and the second step, the Al _x Ga _1-x N (0 <x <1) having a desired composition is obtained. The following nucleus 2 can be formed.

  As the second step, there are the following examples.

  In an example of the second step, the source gas of N is supplied without supplying the source gas of Al and the source gas of Ga, and the substrate temperature, which is the temperature of the single crystal substrate 1, is used as the substrate in the first step. Heat treatment is performed in a state set higher than the temperature. The substrate temperature for this heat treatment may be 1300 ° C., for example. Further, the heat treatment time for this heat treatment may be, for example, 2 minutes. In short, the heat treatment may be performed for 2 minutes at a substrate temperature of 1300 ° C. The substrate temperature for the heat treatment in the second step is not limited to 1300 ° C. However, if the substrate temperature is too low, Ga is not desorbed, and if the substrate temperature is too high, not only Ga but also Al is desorbed. For this reason, it is preferable to set the substrate temperature within a range of about 1100 ° C. to 1350 ° C., for example, capable of desorbing Ga and suppressing desorption of Al. Is more preferable. The heat treatment time may be set as appropriate based on the composition ratio and structure of the nucleus 2, the substrate temperature at which the heat treatment is performed, and the like.

In another example of the second step, an N source gas is supplied without supplying an Al source gas and a Ga source gas, and the substrate temperature which is the temperature of the single crystal substrate 1 is set to the first step. The supply amount of H ₂ gas (hydrogen gas) supplied to the reaction furnace without lowering the substrate temperature in the step is more than the supply amount of H ₂ gas which is a carrier gas for transporting the raw material gas in the first step. The heat treatment is performed in a state where many are set. The supply amount of H ₂ gas in each of the first step and the second step may be, for example, 5 L / min (5 SLM) in the standard state and 10 L / min (10 SLM) in the standard state. In addition, the value of the supply amount of H ₂ gas in each of the first step and the second step is not particularly limited.

The ultraviolet light emitting device of the present embodiment described above embeds a gap between the single crystal substrate 1, the plurality of island-like nuclei 2 formed on one surface of the single crystal substrate 1, and the adjacent nuclei 2. The buffer layer 3 is provided on the one surface side of the single crystal substrate 1 so as to cover all the nuclei 2. Furthermore, the ultraviolet light emitting element includes an n _-type nitride semiconductor layer 4 made of n-type Al _z Ga _{1 -zN} (0 <z ≦ 1) formed on the buffer layer 3, and the n-type nitride semiconductor layer 4. The light emitting layer 5 having the quantum well structure and the p-type nitride semiconductor layer 7 are provided. Here, in the ultraviolet light emitting element, the n-type nitride semiconductor layer 4 is made of n-type Al _z Ga _{1 -z} N (0 <z ≦ 1), and the well layer 5b of the quantum well structure is Al _a Ga _{1− a} N (0 <a ≦ 1). In the ultraviolet light emitting element, the nucleus 2 is made of Al _x Ga _1-x N (0 <x <1), the buffer layer 3 is made of Al _y Ga _1-y N (0 <y ≦ 1), x <y.

In the ultraviolet light emitting element, the nucleus 2 is made of Al _x Ga _1-x N (0 <x <1), while the buffer layer 3 is made of Al _y Ga _1-y N (0 <y ≦ 1), and x <y Therefore, as compared with the conventional case where AlN nuclei are formed or the composition of the nuclei 2 is set to the same composition as that of the buffer layer 3, the group III on the one surface of the single crystal substrate 1 is produced at the time of manufacture. It becomes possible to increase the average diffusion length of atoms. Therefore, in the ultraviolet light emitting device of this embodiment, the density of the nuclei 2 can be reduced. Accordingly, threading dislocations can be reduced in the ultraviolet light emitting device of this embodiment. In short, in the ultraviolet light emitting device of this embodiment, the threading dislocation density of the buffer layer 3 can be reduced, and the threading dislocation density of the light emitting layer 5 can be reduced. Therefore, in the ultraviolet light emitting device of this embodiment, it is possible to improve the light emission efficiency.

  Further, since each of the plurality of nuclei 2 is formed in an island shape in the ultraviolet light emitting element, stress is not easily applied to the nuclei 2, and cracks are less likely to occur while increasing the thickness of the buffer layer 3. . As a result, the ultraviolet light-emitting element can further reduce the threading dislocation density. In addition, the ultraviolet light emitting element can reduce the warpage of the wafer at the time of manufacture, and is easy to handle. As a result, the ultraviolet light-emitting element can improve mass productivity and manufacturing yield.

In the ultraviolet light emitting element, y = 1 may be set for y which is the Al composition of the buffer layer 3 made of Al _y Ga _1-y N (0 <y ≦ 1). In this case, in the ultraviolet light emitting element, the buffer layer 3 is AlN. Since the band gap energy of AlN is 6.2 eV, even if the light emitting layer 5 is designed so that the ultraviolet light emitting element emits ultraviolet light having an emission wavelength of about 220 nm, the ultraviolet light emitted from the light emitting layer 5 is used. Light can be prevented from being absorbed by the buffer layer 3 and is efficiently extracted.

Further, the ultraviolet light-emitting element has an Al composition of Al _x Ga _1-x N (0 <x <1) constituting the nucleus 2 and Al _a Ga _1-a N (0) constituting the well layer 5b. Regarding the relationship with a which is the composition of Al in <a ≦ 1), it is preferable that a <x. Thereby, the ultraviolet light emitting element can further reduce the nuclear density and the dislocation density, and the ultraviolet light emitted from the well layer 5b is efficiently extracted without being absorbed by the nucleus 2. In the ultraviolet light emitting element, when extracting ultraviolet light from the single crystal substrate 1 side, it is important to satisfy a <x in order to improve luminous efficiency.

In addition, the ultraviolet light emitting element has a composition of Al in Al _x Ga _1-x N (0 <x <1) constituting the nucleus 2 and an n-type Al _z Ga constituting the n-type nitride semiconductor layer 4. Regarding the relationship with z which is the composition of Al in _1-zN (0 <z ≦ 1), it is preferable that z <x. Thereby, in the ultraviolet light emitting element, the lattice constant of the nucleus 2 is smaller than the lattice constant of the n-type nitride semiconductor layer 4, so that the n-type nitride semiconductor layer 4 is also subjected to compressive stress from the nucleus 2. Cracks are unlikely to occur in the shaped nitride semiconductor layer 4.

  In the ultraviolet light emitting element, the single crystal substrate 1 is preferably a c-plane sapphire substrate. Thereby, since the single crystal substrate 1 is excellent in ultraviolet light transmittance, the light emitting efficiency of the ultraviolet light emitting element can be improved.

The above-described method for manufacturing an ultraviolet light emitting device includes a first step of forming a plurality of nuclei 2 on the one surface of the single crystal substrate 1 after the single crystal substrate 1 is prepared and placed in a reaction furnace, Second step of forming buffer layer 3, third step of forming n-type nitride semiconductor layer 4, fourth step of forming light emitting layer 5, and fifth step of forming p-type nitride semiconductor layer 7 And. And in the manufacturing method of the above-mentioned ultraviolet light emitting element, it is preferable to make a 1st process into the process provided with the 1st step and the 2nd step. The first step is to supply the Al source gas, the Ga source gas, and the N source gas in a predetermined molar ratio into the reaction furnace at a predetermined molar ratio under the first substrate temperature and the first growth pressure. Forming a crystal nucleus composed of a plurality of Al _b Ga _1-b N (0 <b <1 and b <x) on the one surface. In the second step, a crystal nucleus composed of Al _b Ga _1-b N (0 <b <1 and b <x) is converted into a nucleus 2 composed of Al _x Ga _1-x N (0 <x <1). In this step, Ga is desorbed. Thereby, in the manufacturing method of the ultraviolet light emitting element of this embodiment, the ultraviolet light emitting element which can reduce a threading dislocation can be provided. In addition, from the viewpoint of promoting the diffusion of group III atoms in the first step, the ultraviolet light emitting element preferably has a small Al composition in the nucleus 2, but there is a concern that cracks may occur as the Al composition decreases. There is a concern that the ultraviolet light emitted from the well layer 5b is absorbed by the nucleus 2. On the other hand, in the manufacturing method of the ultraviolet light emitting element of the present embodiment, the first step is a step including the first step and the second step described above, so that the average of group III atoms in the first step is increased. It is possible to reduce the nucleus density by increasing the diffusion length of, and to form the nucleus 2 having a composition ratio capable of preventing absorption of ultraviolet light having a desired emission wavelength in the second step.

  As growth conditions that influence the density of the nuclei 2, the substrate temperature, the V / III ratio, the supply amount of each source gas, the growth pressure, and the like are conceivable. However, in order to diffuse Al atoms on the one surface side of the single crystal substrate 1, it is necessary to give kinetic energy to the Al atoms at the substrate temperature. If the kinetic energy is small, parameters other than the substrate temperature are set. Even if it is changed, since the diffusion length is short, it is difficult to control the density of the nuclei 2. Al has a shorter diffusion length than Ga. For this reason, in order to manufacture an ultraviolet light-emitting device in which the absorption of ultraviolet light by the nucleus 2 can be prevented and the nucleus density can be reduced, the important parameter in the first step is the mol of TMAl in the group III source gas. The ratio ([TMAl] / {[TMAl] + [TMGa]}) is considered to be the substrate temperature.

  In this manufacturing method, in the second step, an N source gas is supplied without supplying an Al source gas and a Ga source gas, and the substrate temperature, which is the temperature of the single crystal substrate 1, is set in the first step. It is preferable to perform the heat treatment in a state set higher than the substrate temperature in step (b). Thereby, in this manufacturing method, since the desorption of Ga is promoted by making the substrate temperature for the heat treatment higher than the substrate temperature in the first step, the second step can be completed in a relatively short time. It becomes possible, and it becomes possible to improve productivity.

  In this manufacturing method, in the second step, N source gas is supplied without supplying Al source gas and Ga source gas, and the substrate temperature, which is the temperature of the single crystal substrate 1, is set. A state in which the supply amount of hydrogen gas supplied to the reactor is set higher than the supply amount of hydrogen gas, which is a carrier gas for transporting the raw material gas, in the first step without lowering the substrate temperature in one step. It is preferable to perform the heat treatment. Thereby, in this manufacturing method, since the desorption of Ga is promoted by increasing the flow rate of the reducing gas, hydrogen gas, in the second step, the second step can be completed in a relatively short time. Thus, productivity can be improved.

(Embodiment 2)
Below, the ultraviolet light emitting element of this embodiment is demonstrated based on FIG.

  The ultraviolet light emitting element of this embodiment is different from the ultraviolet light emitting element of Embodiment 1 in the structure of the nucleus 2. In addition, about the component similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As for the nucleus 2 in the ultraviolet light emitting element of this embodiment, it is preferable that x which is a composition of Al becomes large as it leaves | separates from the single crystal substrate 1. FIG.

(Embodiment 2)
In the ultraviolet light emitting device of this embodiment, each of the plurality of island-like nuclei 2 made of Al _x Ga _1-x N (0 <x <1) is formed on the one surface of the single crystal substrate 1. _0.7 Ga _0.3 N 2a and Al _0.9 Ga _0.1 N 2b formed on the Al _0.7 Ga _0.3 N 2a . In the ultraviolet light emitting device of this embodiment, the height dimension of Al _0.7 Ga _0.3 N 2a in the normal direction of the one surface of the single crystal substrate 1 is 5 nm, and the height dimension of Al _0.9 Ga _0.1 N 2b is 5 nm. Although set, these values are merely examples and are not particularly limited.

  In the ultraviolet light-emitting device of this embodiment, it is possible to suppress the occurrence of new defects due to the difference in lattice constant between the nucleus 2 and the buffer layer 3, thereby reducing the dislocation density and improving the light emission efficiency. It becomes possible.

  In the ultraviolet light emitting device of the present embodiment, x which is the composition of Al in the nucleus 2 changes in two steps in the normal direction, but is not limited to this, and may be three or more steps, or continuously changed. The configuration may be also possible.

  The manufacturing method of the ultraviolet light emitting element of the present embodiment is basically the same as the manufacturing method described in the first embodiment, and if the growth conditions in the first step are appropriately changed based on the configuration of the desired nucleus 2. Good.

  In the ultraviolet light emitting elements of the first and second embodiments, since the light emission wavelength of the light emitting layer 5 is set in the range of 210 nm to 360 nm, a light emitting diode having a light emission wavelength in the ultraviolet region can be realized. It can be used as an alternative light source for deep ultraviolet light sources such as.

1 single crystal substrate 2 nucleus 3 buffer layer 4 n-type nitride semiconductor layer 5 light emitting layer 5b well layer 7 p-type nitride semiconductor layer

Claims (9)

Filling a gap between a single crystal substrate, a plurality of island-shaped nuclei formed of Al _x Ga _1-x N (0 <x <1) formed on one surface of the single crystal substrate, and the adjacent nuclei; A buffer layer made of Al _y Ga _1-y N (0 <y ≦ 1) formed on the one surface side of the single crystal substrate so as to cover all the nuclei, and n formed on the buffer layer An n-type nitride semiconductor layer made of type Al _z Ga _1-z N (0 <z ≦ 1) and Al _a Ga _1-a formed on the opposite side of the n-type nitride semiconductor layer from the buffer layer side A light emitting layer having a quantum well structure having a well layer made of N (0 <a ≦ 1), and a p-type nitride semiconductor layer formed on a side opposite to the n-type nitride semiconductor layer side in the light emitting layer. An ultraviolet light emitting device comprising x <y.   The ultraviolet light-emitting element according to claim 1, wherein y = 1.   The ultraviolet light-emitting device according to claim 1, wherein a <x.   The ultraviolet light-emitting device according to claim 1, wherein z <x.   5. The ultraviolet light emitting element according to claim 1, wherein x of the composition of Al increases as the nucleus moves away from the single crystal substrate. 6.   The ultraviolet light-emitting element according to claim 1, wherein the single crystal substrate is a c-plane sapphire substrate. 7. The method for manufacturing an ultraviolet light emitting element according to claim 1, wherein after the single crystal substrate is prepared and placed in a reaction furnace, a plurality of the light emitting elements are formed on the one surface of the single crystal substrate. A first step of forming the nucleus, a second step of forming the buffer layer, a third step of forming the n-type nitride semiconductor layer, a fourth step of forming the light emitting layer, and the p And a fifth step of forming a shaped nitride semiconductor layer, wherein the first step includes an Al source gas, a Ga source gas, and an N source in the reactor at a first substrate temperature and a first growth pressure. Crystal nucleus composed of a plurality of Al _b Ga _1-b N (0 <b <1 and b <x) on the one surface of the single crystal substrate by supplying a raw material gas at a predetermined molar ratio And a first step of forming Al _b Ga _1-b N (0 <b <1 and b <x). And a second step of desorbing Ga so that the crystal nucleus is the nucleus composed of Al _x Ga _1-x N (0 <x <1). In the second step, the source gas of N is supplied without supplying the source gas of Al and the source gas of Ga, and the substrate temperature, which is the temperature of the single crystal substrate, is set in the first step. The method of manufacturing an ultraviolet light emitting element according to claim 7, wherein the heat treatment is performed in a state set higher than the first substrate temperature in the step. In the second step, the source gas of N is supplied without supplying the source gas of Al and the source gas of Ga, and the substrate temperature, which is the temperature of the single crystal substrate, is set in the first step. The supply amount of hydrogen gas supplied to the reactor without lowering the temperature of the first substrate in step 1 is set to be higher than the supply amount of hydrogen gas that is a carrier gas for transporting the source gas in the first step. 8. The method of manufacturing an ultraviolet light-emitting element according to claim 7, wherein the heat treatment is performed in a set state.

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