JP2012080010A - Epitaxial wafer, semiconductor element, and method of manufacturing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer of a group III-V compound semiconductor having excellent crystallinity while having an Sb-containing layer, to provide a semiconductor element using the epitaxial wafer, and to provide a method of manufacturing them.SOLUTION: A method of manufacturing an epitaxial wafer of the present invention comprises the step of alternately and periodically growing a GaAsSb layer 3a and an InGaAs layer 3b on a substrate 1 by a vapor phase epitaxial method. In growing the GaAsSb layer, the substrate temperature is set and a material gas is supplied so that the Sb mole fraction xin a group V of the GaAsSb layer and the Sb mole fraction xin a group V of the supplied material gas (gas phase) satisfy the following formula: 0.75≤(x/x)≤1.20.

Description

  The present invention relates to an III-V group compound semiconductor epitaxial wafer, a semiconductor device, and a method for manufacturing the same, and more specifically, type 2 having a band gap energy corresponding to a long wavelength region of near infrared. The present invention relates to an epitaxial wafer including a multiple-quantum well structure, a semiconductor device, and a manufacturing method thereof.

Since an InP-based semiconductor of a III-V compound has a band gap energy corresponding to the near infrared region, much research and development has been conducted for light receiving elements for communication and night imaging.
For example, a photodiode having a cutoff wavelength of 2 μm or more has been proposed by forming an InGaAs / GaAsSb type 2 multiple quantum well structure (MQW) on an InP substrate (Non-patent Document 1). This MQW is growing by MBE (Molecular Beam Epitaxy) method.
In addition, an LED and a laser diode having an emission wavelength of 2.14 μm are proposed in which InGaAs / GaAsSb type 2 MQW is formed on an InP substrate as an active layer (Non-patent Document 2). This type 2 MQW is grown at a temperature of 530 ° C. by a metal-organic vapor phase epitaxy (MOVPE) method. As for the raw materials of InGaAs and GaAsSb, the respective organometallic gases are disclosed.

R. Sidhu, et.al. "ALong-Wavelength Photodiode on InP Using Lattice-Matched GaInAs-GaAsSb Type-II Quantum Wells, IEEE Photonics Technology Letters, Vol.17, No.12 (2005), pp.2715-2717 M.Peter, et.al. “Light-emitting diodes and laser diodes based on a Ga1-xInxAs / GaAs1-ySbytype II superlattice on InP substrate” Appl. Phys. Lett., Vol.74, No.14 (5 April 1999 ), pp.1951-1953

The above photodiodes do not have sufficient performance levels such as sensitivity and dark current, have large variations between light receiving elements (chips) in the epitaxial wafer, and manufacture the epitaxial wafer stably and with good reproducibility. Is difficult. This is due to the growth method by the MBE method.
In addition, the performance level of the light-emitting diode is not good, and it is difficult to manufacture the epitaxial wafer with good reproducibility and variations between chips in the same epitaxial wafer. This is due to the growth method described above. In particular, the amount of Sb incorporated into the solid phase varies greatly with only a slight change in growth temperature or substrate temperature. The Sb composition of the layer containing Sb is unstable, and the Sb-containing layer tends to cause phase separation or the like at a predetermined temperature or higher, and it is difficult to obtain good crystals.

  An object of the present invention is to provide an III-V compound semiconductor epitaxial wafer having excellent crystallinity, a semiconductor element, and a method for manufacturing these, while having an Sb-containing layer. Note that excellent crystallinity includes not only the meaning of a crystal that provides good performance in a semiconductor element, but also the meaning that a surface defect or the like that reduces the manufacturing yield is suppressed.

The epitaxial wafer manufacturing method of the present invention manufactures an III-V compound semiconductor epitaxial wafer on a substrate. This method includes a step of alternately and repeatedly growing a first layer containing Sb and a second layer not containing Sb on a substrate by a vapor phase growth method. The Sb mole fraction x ₁ in the group V of the first layer (solid phase) and the Sb mole fraction x ₂ in the group V of the supplied source gas (gas phase) are 0.75. The substrate temperature is set so as to satisfy ≦ (x ₁ / x ₂ ) ≦ 1.20, and the source gas is supplied.

According to the above method, the first layer containing Sb becomes difficult to phase-separate both during the growth of the first layer and during growth of the layers above the first layer, and a good crystal quality can be obtained. . As a result, a semiconductor device having good performance can be obtained using this epitaxial wafer.
In addition, the variation in the Sb composition with respect to the variation in temperature is reduced, and the stability during manufacturing is improved. That is, the uniformity in the same epitaxial wafer can be improved, and the epitaxial wafer or each lot can be manufactured with good reproducibility. As a result, the manufacturing yield can be increased and the manufacturing cost can be reduced.
(X ₁ / x ₂ ) will be referred to as the Sb solid phase concentration rate. When the Sb solid phase concentration rate is less than 0.75, Sb is less likely to be incorporated into the solid phase as compared to As. . For this reason, the stoichiometrically normal range of GaAsSb deviates to the Sb-deficient side, and good crystalline GaAsSb cannot be obtained. Also, surface defects are likely to occur during or after the growth of layers above the MQW. On the other hand, when the Sb solid phase concentration rate exceeds 1.20, Sb is likely to be excessively incorporated into the solid phase. For this reason, it will deviate from the stoichiometrically normal range of GaAsSb to the Sb excess side, and it is not possible to obtain GaAsSb with good crystallinity.
The substrate temperature is a substrate surface temperature monitored by a pyrometer including an infrared camera and an infrared spectrometer. Accordingly, although it is the substrate surface temperature, strictly speaking, it is the temperature of the epitaxial layer surface in a state where a film is formed on the substrate. There are various names such as a substrate temperature, a growth temperature, and a film formation temperature, and all refer to the monitored temperatures.

  The substrate temperature during the growth of the first layer can be 390 ° C. or higher and 490 ° C. or lower. As a result, it is possible to obtain a first layer that includes Sb and has excellent crystallinity. In particular, when the source gas is supplied in accordance with the Sb composition x1 of the first layer, the Sb solid phase concentration rate is set in the range of 0.75 to 1.20 by taking this substrate temperature range. Can do.

  The substrate temperature during the growth of the first layer can be made lower than the substrate temperature during the growth of the second layer. Thus, both the first layer containing Sb and the second layer not containing Sb can be made excellent in crystallinity. As a result, it is possible to obtain MQW excellent in crystallinity in which both are paired.

The substrate temperature during the growth of the second layer can be higher by 20 ° C. than the substrate temperature during the growth of the first layer.
As a result, both the first layer containing Sb and the second layer not containing Sb can be grown at a temperature suitable for growth, resulting in excellent manufacturing stability and high-quality MQW. be able to.

After the growth of the second layer, the first layer can be grown after the substrate temperature is surely lowered to the temperature at the time of the growth of the first layer.
In this case, it can be ensured that the temperature drops and the entire temperature reaches the set temperature uniformly, and high quality can be maintained.

After the growth of the second layer, the first layer can begin to grow while the temperature is lowered to the substrate temperature during the growth of the first layer.
When growth is performed in the middle of lowering the temperature, the Sb composition in the first layer increases as the substrate temperature decreases. For this reason, a gradient concentration portion of Sb is formed. That is, in the first layer, a gradient concentration portion in which the Sb concentration increases in a direction away from the substrate is formed. In general, when the Sb concentration increases, the energy of the conduction band decreases and the energy of the valence band increases. Therefore, the wave function of the holes is shifted in the direction away from the substrate. Since the energy band of the partner layer (second layer) paired with the type 2 MQW does not change unless the composition has a gradient, the electron wave function is located at the center of the quantum well in the second layer. As a result, the overlap between the wave function of holes in the Sb-containing layer and the wave function of electrons in the second layer increases, and the quantum efficiency of the transition phenomenon that crosses the interface between both layers in type 2 MQW increases. It will be. As a result, for example, in the light receiving element, the light receiving sensitivity on the long wavelength side in the near infrared region is improved. For this reason, even if the number of MQW pairs is reduced, the light receiving sensitivity on the long wavelength side can be maintained.
Further, since it takes time until the substrate temperature is stabilized (from the temperature rise) when the substrate temperature is lowered, it is possible to shorten the production time and reduce the production cost by growing during the temperature fall.

After the growth of the first layer, the second layer is grown after the substrate temperature is surely raised to the temperature at the time of the growth of the second layer, or the second layer is raised during the temperature rise. You can start growing layers of.
The second layer can also benefit from shortened growth time. However, temperature rise does not take time to stabilize compared to temperature drop.

The first layer can be any one of GaAsSb, AlAsSb, and InAsSb.
By using these materials, a light receiving element having a cutoff wavelength at a wavelength of 2 μm or more and a light emitting element having a peak wavelength at a wavelength of 2 μm or more can be obtained.

The first layer can be GaAs _1-x Sb _x (0 <x ≦ 1), and the second layer can be In _y Ga _1-y As (0 <y ≦ 1).
As a result, type 2 MQW can be obtained. As a result, it is possible to obtain a light receiving element having a cut-off wavelength at a wavelength of 2 μm or more and a small dark current, or a light emitting element having a peak wavelength at a wavelength of 2 μm or more or having a high light emission efficiency.

The substrate can be any one of GaAs, GaP, GaSb, InP, InAs, InSb, AlSb, and AlAs.
Using these substrates, high-quality epitaxial wafers used for various near-infrared light-receiving elements or light-emitting elements can be manufactured.

The vapor deposition method can be an all-organic metal vapor deposition method. Accordingly, the substrate temperature during the growth of the first layer and the second layer and the substrate temperature during the growth of the other upper layer (for example, the window layer or the diffusion concentration adjusting layer) can be reduced as compared with other vapor phase growth methods. Both can be lowered. As a result, an epitaxial wafer having excellent crystallinity can be obtained. Especially for the first layer containing Sb, not only high-quality crystals can be obtained by lowering the substrate temperature of the first layer, but also the substrate temperature of the second layer and other upper layers can be lowered. In addition, problems such as phase separation that occurs when the temperature is raised later can be eliminated.
Here, the all organic vapor phase growth method refers to a growth method using an organic metal raw material composed of a compound of an organic substance and a metal for all raw materials used for vapor phase growth, and is referred to as an all organic MOVPE method. The advantages of the all organic MOVPE method are many as will be described later, but the most widely is that each layer can be grown efficiently.

In the method for manufacturing a semiconductor device of the present invention, an epitaxial wafer manufactured by any one of the above manufacturing methods can be used.
As a result, a high-performance semiconductor element can be obtained using an epitaxial wafer having a high-quality crystal and high economy while incorporating an Sb-containing layer. Any semiconductor element may be used, for example, a light receiving element or a light emitting element.

The epitaxial wafer of the present invention is an III-V group compound semiconductor epitaxial wafer having a substrate and an epitaxial layer located thereon. In this epitaxial wafer, the first layer containing Sb and the second layer not containing Sb are alternately positioned on the substrate, and the first layer has a high Sb concentration in a direction away from the substrate. There is a gradient concentration portion.
With the above structure, a process for forming the first layer in the middle of temperature reduction can be used, and productivity can be improved. Furthermore, since the source gas having a constant Sb mole fraction in the group V can be supplied during the growth of the first layer in the middle of temperature reduction, the manufacturing process can be simplified and facilitated.
Furthermore, the first layer containing Sb usually has a higher valence band potential value than the second layer. In the type 2 MQW, for example, in light reception, holes are generated in the first layer having a higher valence band potential value, and electrons are generated in pairs in the second layer. Since the Sb concentration of the first layer increases toward the second layer on the upper side, the energy at the bottom (vacuum) of the valence band of the first layer is directed toward the second layer on the upper side. And deepen. For this reason, the wave function of holes shifts so as to approach the wave function of electrons in the adjacent second layer. If the second layer is not grown in the middle of the temperature rise, it has a rectangular well potential, so the electron wave function is located in the center of the second layer. As a result, the overlap of the wave functions of holes and electrons increases, and the quantum efficiency of light reception can be improved. That is, the sensitivity can be increased.
Also in light emission, since the transition probability that electrons in the conduction band transition to the adjacent valence band increases, the light emission efficiency can be improved.

The first layer can be any one of GaAsSb, AlAsSb, and InAsSb.
By using this epitaxial wafer, a light receiving element having a cutoff wavelength at a wavelength of 2 μm or more, or a light emitting element having a peak wavelength at a wavelength of 2 μm or more can be obtained.

The first layer can be GaAs _1-x Sb _x (0 <x ≦ 1), and the second layer can be In _y Ga _1-y As (0 <y ≦ 1).
As a result, type 2 MQW can be obtained. According to this MQW, it is possible to obtain a light receiving element having a cut-off wavelength at a wavelength of 2 μm or more and a small dark current, or a light emitting element having a peak wavelength at a wavelength of 2 μm or more and having a high luminous efficiency.

The substrate can be any one of GaAs, GaP, GaSb, InP, InAs, InSb, AlSb, and AlAs.
By using these substrates, it is possible to easily obtain a light receiving element having a cut-off wavelength at a wavelength of 2 μm or more, and a light emitting element having a peak wavelength at a wavelength of 2 μm or more, having good element characteristics.

  According to the method for manufacturing an epitaxial wafer of the present invention, it is possible to obtain an excellent crystallinity while having an Sb-containing layer.

(A) Sectional drawing of epitaxial wafer in Embodiment 1 of this invention, (b) The enlarged view of MQW which comprises a light reception layer. (A) The figure explaining the condition at the time of the growth of GaAsSb in MQW of FIG. 1, (b) The figure which shows the range of Sb solid-phase concentration rate. It is a figure which shows the relationship between Sb solid-phase concentration rate and growth temperature. It is a figure which shows the growth sequence of MQW. (A) Band diagram when GaAsSb layer in type 2 MQW has a concentration gradient portion and diagram showing positions of wave functions of electrons and holes, (b) Band diagram and electron of conventional type 2 MQW It is a figure which shows the position of the wave function of a hole. It is a figure which shows the piping system etc. of the film-forming apparatus of all the organic MOVPE method. It is a figure which shows the light receiving element array (semiconductor element) in Embodiment 2 of this invention. It is a figure which shows the light receiving element in Embodiment 2 of this invention. It is a flowchart of the manufacturing method of the light receiving element 50 of FIG. (A) is a figure which shows the light emitting element (LED) in Embodiment 3 of this invention, (b) is an enlarged view of MQW. In Example 3 of the present invention, it is a diagram showing a relationship between Sb molar ratio _{x 2} of Sb molar ratio _{x 1} and the raw material gas in the GaAsSb.

(Embodiment 1-Epitaxial wafer)
1A and 1B show an epitaxial wafer 1a according to an embodiment of the present invention, where FIG. 1A is an overall cross-sectional view, and FIG. 1B is a type 2 MQW in which a GaAsSb 3a and an InGaAs 3b constituting a light receiving layer 3 are paired. FIG. The epitaxial wafer 1a includes an InP substrate 1, a buffer layer 2, and an epitaxial layer 7 located thereon. The epitaxial layer 7 is grown by the all-organic MOVPE method, and the contents of the epitaxial layer 7 including the buffer layer 2 are as follows.
(InP substrate 1 / n-type InP buffer layer 2 / type 2 (InGaAs / GaAsSb) MQW light receiving layer 3 / InGaAs diffusion concentration distribution adjusting layer 4 / InP window layer 5)
As shown in FIG. 1B, the MQW 3 is formed by repetition of GaAsSb (first layer) 3a containing Sb and InGaAs (second layer) 3b containing no Sb. Since GaAsSb contains Sb, it has heretofore been difficult to grow a film with good crystallinity without variation within the same wafer and with good reproducibility between wafers. In order to give this GaAsSb3a good crystallinity and grow with good reproducibility, the present embodiment adopts the following measures as shown in FIG.

FIG. 2A is a schematic diagram of source gas and the like when growing GaAsSb (first layer) 3a in MQW3 shown in FIG. 1B, and FIG. 2B shows source gas and Sb mole in GaAsSb3a. It is a figure which shows the conditions imposed on ratio (molar fraction). In the all organic MOVPE method, the source gas is supplied in the form of a hydrocarbon metal in which a group 3 or group 5 metal and a hydrocarbon are combined. Since hydrocarbon metal is easily decomposed at a relatively low temperature, it is suitable for the growth of a compound that is easily phase-separated by a temperature rise, such as GaAsSb containing Sb. Trimethylantimony (TMSb) exemplified as the antimony source gas supplies Sb to the growth surface while decomposing at or near the surface of the growing GaAsSb layer 3a. Similarly, Ga and As source gases are decomposed to supply Ga and As. Here, Sb and As are the same group V elements, and together they form the same number of atoms (number of moles) as group 3 Ga and constitute GaAsSb. The Sb or As source gas is introduced into the quartz tube 65 located in the growth chamber by opening and closing a valve while independently controlling the supply amount with an MFC (Mass Flow Controller), as will be described in detail later. At this time, the molar ratio of Sb and As in the source gas is [Sb] / [As] = as shown in FIG. 2A regardless of the method of supplying each source gas. x ₂ / (1-x ₂ ).
The GaAsSb 3a to be grown can be expressed as GaAs _1-x1 Sb _x1 (0.36 ≦ x ₁ ≦ 0.62) if a specific example of a composition range desirable for the light receiving element is displayed. For InGaAs, In _z Ga _1-z As (0.38 ≦ z ≦ 0.68). In the following description, GaAsSb or the like is displayed without displaying the composition ratio.
Sb is an element that is so difficult to control that it has high mobility and is very difficult to handle. For this reason, when Sb in the source gas is excessive and insufficient with respect to the growing solid phase, good crystals cannot be obtained in each case. That is, the x ₂ in the source gas must be in the following range with respect to x ₁ in GaAs _1-x1 Sb _x1 .
0.75 ≦ x ₁ / x ₂ ≦ 1.20 (1)
In the above formula (1), (Sb molar ratio in the V group in the solid phase) / Sb molar ratio in the V group in the gas phase) (= x ₁ / x ₂ ) is referred to as the Sb solid phase concentration ratio. To do. When the Sb solid phase concentration rate is less than 0.75, Sb is less likely to be taken into the solid phase as compared to As. For this reason, it deviates from the stoichiometrically normal range of GaAs _1-x1 Sb _x1, and it is not possible to obtain GaAsSb3a having good crystallinity. Further, Sb in the gas phase becomes excessive. Although it is just speculation, it is considered that excessive Sb in the gas phase forms an Sb enriched layer that is not solid-phased (crystallized) on the growth surface. As a result, surface defects are caused during or after the growth of the upper layer than MQW3. The surface defects are often generated not only during the growth of GaAsSb but also after the growth of MQW3 is completed and the InP window layer 5 is pushed up from below during or after the growth of the InP window layer 5. This type of surface defect has a height of 10 μm or more, and a large one reaches a height of 100 μm, which significantly reduces the manufacturing yield.
On the other hand, when the Sb solid phase concentration rate exceeds 1.20, Sb is likely to be excessively incorporated into the solid phase. For this reason, it deviates from the stoichiometrically normal range of GaAs _1-x1 Sb _x1 , and in this case as well, good crystalline GaAsSb3a cannot be obtained.
In short, if the Sb solid phase concentration rate deviates from the range of the formula (1), it is not possible to obtain an excellent crystalline epitaxial wafer 1a.

Then, what should be done to bring the Sb solid phase concentration rate into the range of the formula (1)? FIG. 3 is a diagram showing the relationship between the Sb solid phase concentration rate (x ₁ / x ₂ ) and the substrate temperature (growth temperature). The data in FIG. 3, a raw material gas (TMSb) and As in the raw material gas Sb (TMAs), but as the molar ratio _{1-x 2} molar ratio _x 2, As and Sb in the feed gas, the _{x 2} , those taken in the case of supplying to fit the _{x 1} in the range, 0.38 ≦ _{x 1} ≦ 0.68, in the GaAsSb.
According to FIG. 3, it can be seen that when the Sb solid phase concentration rate is in the range of equation (1), the substrate temperature may be set to 390 ° C. or higher and 490 ° C. or lower. This temperature range is quite low, for example a special growth temperature for the growth of GaAsSb that is 20 ° C. or more lower than the growth temperature of InGaAs3b.

  FIG. 4 is a diagram showing a growth temperature and source gas supply sequence when growing MQW3 composed of repetition of GaAsSb3a and InGaAs3b. The substrate temperature (growth temperature) Tg during the growth of InGaAs3b is set to 500 ° C., and the substrate temperature Tg during the growth of GaAsSb3a is set to 450 ° C. Therefore, it is necessary to lower the substrate temperature Tg after growing InGaAs3b and before growing GaAsSb3a. It takes longer to stabilize the substrate temperature Tg when it is lowered than when it is raised. When 250 pairs of InGaAs3b and GaAsSb3a are grown, shortening the growth time is important in terms of manufacturing efficiency, and in particular, shortening the time required for temperature drop is important. For this reason, as shown in FIG. 4, the growth start of GaAsSb3a does not wait for the substrate temperature Tg to stabilize at 450 ° C., for example, even while the temperature is decreasing toward 450 ° C. Good. That is, GaAsSb may be grown from a temperature higher than a predetermined range from 450 ° C. By such growth of GaAsSb during temperature reduction before temperature stabilization, the growth time of MQW3 can be shortened and the manufacturing efficiency can be improved.

The lower the growth temperature, the higher the Sb molar ratio in GaAsSb3a. For this reason, the growth of GaAsSb3a during the temperature drop results in a thickness portion in which the composition is partially inclined. As shown in FIG. 5A, in the thickness portion where the concentration of Sb is high, the conduction band energy Ec decreases with respect to the electrons, and the valence band energy Ev increases with respect to the electrons. The opposite is true for holes. In InGaAs / GaAsSb type 2 MQW, since the energy of the valence band of GaAsSb is higher than that of InGaAs, holes are located in GaAsSb3a. There is a higher probability that holes located in the valence band of GaAsSb3a are located in the quantum well where the potential energy Ev is lower. That is, the wave function of holes in the valence band Ev of GaAsSb shifts its position toward the higher Sb molar ratio. On the other hand, since InGaAs3b has no concentration gradient, the electron wave function of the conduction band is located at the center of the quantum well. As a result, in MQW3 provided with GaAsSb3a having an Sb concentration gradient portion, the overlap between the hole wave function in GaAsSb3a and the electron wave function in InGaAs3b increases, and the quantum efficiency can be increased. As a result, the light receiving sensitivity is improved in the light receiving element, and the light emission efficiency is improved in the light emitting element.
FIG. 5B is a band diagram of MQW without a concentration gradient portion of Sb, and holes and electrons are positioned in alignment with the centers of the quantum wells of the valence band and the conduction band, respectively. For this reason, in the conventional MQW, the quantum efficiency does not change due to the modulation of the band structure.

The growth of each layer is performed by the all organic MOVPE method having a high growth efficiency as described above. FIG. 6 shows a piping system and the like of the all-organic MOVPE film forming apparatus 60. A quartz tube 65 is disposed in the reaction chamber (chamber) 63, and a raw material gas is introduced into the quartz tube 65. A substrate table 66 is disposed in the quartz tube 65 so as to be rotatable and airtight. The substrate table 66 is provided with a heater 66h for heating the substrate. The temperature of the surface of the epitaxial wafer 1 a during film formation is monitored by the infrared temperature monitor device 61 through a window 69 provided in the ceiling portion of the reaction chamber 63. This monitored temperature is a temperature at the time of growth or a temperature called a film forming temperature or a substrate temperature. In the manufacturing method of the present invention, when GaAsSb3a is grown at a growth temperature or a substrate temperature of 390 ° C. or more and 490 ° C. or less, 390 ° C. or more and 490 ° C. or less are temperatures measured by this temperature monitor. The forced exhaust from the quartz tube 65 is performed by a vacuum pump.
The source gas is supplied by a pipe communicating with the quartz tube 65. The all organic MOVPE method is characterized in that all raw material gases are supplied in the form of an organometallic gas. That is, the source gas takes the form of a metal combined with various hydrocarbons. In FIG. 6, source gases such as impurities that determine the conductivity type are not specified, but impurities are also introduced in the form of an organometallic gas. An organic metal gas source gas is put in a thermostat and maintained at a constant temperature. Hydrogen (H ₂ ) and nitrogen (N ₂ ) are used as the carrier gas. The organometallic gas is transported by a transport gas, and is sucked by a vacuum pump and introduced into the quartz tube 65. The amount of the carrier gas is accurately adjusted by an MFC (flow rate controller). Many flow controllers, solenoid valves, and the like are automatically controlled by a microcomputer.

As a raw material for Ga (gallium), TEGa (triethylgallium) or TMGa (trimethylgallium) may be used. The raw material for In (indium) may be TMIn (trimethylindium) or TEIn (triethylindium). As a raw material of As (arsenic), TBAs (tertiary butylarsine) or TMAs (trimethylarsenic) may be used.
The raw material for Sb (antimony) may be TMSb (trimethylantimony) or TESb (triethylantimony). Further, TIPSb (triisopropylantimony) or TDMASb (tridimethylaminoantimony) may be used. By using these raw materials, an epitaxial wafer 1a with excellent MQW crystal quality can be obtained. As a result, for example, when used in a light receiving element, a light receiving element with a small dark current and a high sensitivity can be obtained. Furthermore, an optical sensor device that can capture a clearer image, such as an imaging device, can be obtained using the light receiving element.

Next, the flow state of the source gas when forming MQW3 will be described. The source gas is transported through the piping, introduced into the quartz tube 65, and exhausted. Any number of source gases can be added to the quartz tube 65 by increasing the number of pipes. For example, even a dozen kinds of source gases are controlled by opening and closing the electromagnetic valve.
The flow rate of the source gas is controlled by a flow rate controller (MFC) shown in FIG. 6, and the flow into the quartz tube 65 is turned on and off by opening and closing the electromagnetic valve. The quartz tube 65 is forcibly exhausted by a vacuum pump. There is no stagnation in the flow of the source gas, and it is performed smoothly and automatically. Therefore, the composition is switched quickly when forming the quantum well pair.
As shown in FIG. 6, since the substrate table 66 rotates, the temperature distribution of the source gas does not have the directivity as on the inlet side or the outlet side of the source gas. Moreover, since the epitaxial wafer 1a revolves on the substrate table 66, the flow of the source gas in the vicinity of the surface of the epitaxial wafer 1a is in a turbulent state. However, even the source gas in the vicinity of the surface of the epitaxial wafer 1a has a large velocity component in the flow direction from the introduction side to the exhaust side except for the source gas in contact with the epitaxial wafer 1a. Therefore, most of the heat flowing from the substrate table 66 to the source gas through the epitaxial wafer 1a is always exhausted together with the exhaust gas.

In the epitaxial wafer 1 a shown in FIG. 1A, the InGaAs diffusion concentration distribution adjustment layer 4 is located on the type 2 MQW 3, and the InP window layer 5 is located on the InGaAs diffusion concentration distribution adjustment layer 4. is doing. From the formation of MQW 3 to the formation of InP window layer 5, it is one point to continue the growth in the same film forming chamber or quartz tube 65 by the all organic MOVPE method. That is, before the InP window layer 5 is formed, the epitaxial wafer 1a is not taken out from the film forming chamber and the InP window layer 5 is not formed by another film forming method. Since the InGaAs diffusion concentration distribution adjusting layer 4 and the InP window layer 5 are continuously formed in the quartz tube 65, the interfaces 16 and 17 are not regrowth interfaces. At the regrowth interface, the oxygen concentration is 1E17 cm ⁻³ or more and the carbon concentration is 1E17 cm ⁻³ or more, the crystallinity is deteriorated, and the surface of the epitaxial laminate is difficult to be smooth. In the present invention, the oxygen and carbon concentrations are both lower than a predetermined level, and charge leakage does not occur particularly at the crossing line between the p-type region 6 and the interface 17 in the light receiving element described later.

In the present embodiment, a non-doped InGaAs diffusion concentration distribution layer 4 having a film thickness of, for example, about 0.3 μm is formed on the MQW 3. After the InP window layer 5 is formed, the InGaAs diffusion concentration distribution layer 4 has a high concentration of Zn when the p-type impurity Zn is introduced from the InP window layer 5 to reach the MQW light receiving layer 3 by a selective diffusion method. When it enters MQW, the crystallinity is damaged, so it is provided for the adjustment. The InGaAs diffusion concentration distribution adjustment layer 4 may be arranged as described above, but may not be provided.
Even when the InGaAs diffusion concentration distribution adjusting layer 4 is inserted, since the InGaAs has a small band gap, the electric resistance of the light receiving element can be lowered even if it is non-doped. By reducing the electrical resistance, it is possible to improve the responsiveness and obtain a moving image with good image quality.
On the InGaAs diffusion concentration distribution adjusting layer 4, the undoped InP window layer 5 is epitaxially grown to a thickness of, for example, about 0.8 μm by the all-organic MOVPE method continuously with the epitaxial wafer 1a placed in the same quartz tube 65. It is good to do. As described above, trimethylindium (TMIn) and tertiary butylphosphine (TBP) are used for the source gas. By using this source gas, the growth temperature of the InP window layer 5 can be lowered. As a result, the MQW GaAsSb positioned under the InP window layer 5 is not damaged by heat, and the density of surface defects can be lowered to a practically acceptable level.

In order to grow an InP window layer by the MBE method, it is necessary to use a solid raw material as a phosphorus raw material, which is problematic in terms of safety. There was also room for improvement in terms of manufacturing efficiency. When the InP window layer 5 is grown by a method other than the MBE method, the interface 17 between the InGaAs diffusion concentration distribution adjusting layer 4 and the InP window layer 5 is a regrowth interface once exposed to the atmosphere. The regrowth interface can be identified by satisfying at least one of the oxygen concentration of 1E17 cm ⁻³ or more and the carbon concentration of 1E17 cm ⁻³ or more by secondary ion mass spectrometry. The regrowth interface forms a crossing line with the p-type region, and a charge leak occurs at the crossing line, thereby significantly degrading the image quality.
Further, for example, when an InP window layer is grown by a simple all-organic MOVPE method, phosphine (PH ₃ ) is used as a raw material of phosphorus, so that the decomposition temperature is high, and the occurrence of damage due to the heat of GaAsSb located in the lower layer is induced. There is a high risk of harming the crystallinity.

(Embodiment 2-light receiving element (semiconductor element)-)
FIG. 7 is a diagram showing the light receiving element 50 according to Embodiment 2 of the present invention. The light receiving element 50 has the following InP-based epitaxial multilayer on the InP substrate 1.
(N-type InP substrate 1 / n-type InP buffer layer 2 / type 2 (InGaAs / GaAsSb) MQW light-receiving layer 3 / InGaAs diffusion concentration distribution adjusting layer 4 / InP window layer 5)
The p-type region 6 located from the InP window layer 5 to the light-receiving layer 3 through the InGaAs layer 4 is formed by selective diffusion of p-type impurity Zn from the opening of the selective diffusion mask pattern 36 of the SiN film. The The p-type region 6 is separated by a region that is not selectively diffused, and becomes a main part of the pixel P. By adjusting the opening of the selective diffusion mask pattern, the p-type region 6 can be formed to be separated from the side surface by a predetermined distance. A p-side electrode 11 made of AuZn is provided in the p-type region 6, and an n-side electrode 12 made of AuGeNi is provided in ohmic contact with the back surface of the InP substrate 1. The InP substrate 1 is doped with an n-type impurity to ensure a predetermined level of conductivity.
The pixels P are arranged vertically and horizontally at a pitch of 30 μm. Sometimes referred to as a light receiving element array. The light receiving element 50 is separated into pieces after the epitaxial wafer 1a shown in FIG. 1 is subjected to predetermined processing such as selective diffusion and electrode formation. Eleven light receiving elements 50 can be obtained from the epitaxial wafer 1a having a diameter of 2 inches.
FIG. 8 is a view showing a light receiving element 50 including a single pixel, and such a light receiving element naturally corresponds to the present invention. In the examples described below, dark current and the like were evaluated by the light receiving element 50 shown in FIG.
FIG. 9 is a flowchart showing a method for manufacturing the light receiving element 50 shown in FIG. 7 or FIG. In step S1, GaAsSb3a in MQW3 is grown by the method described in the first embodiment. Steps S2 to S3 are also the same as the method for manufacturing epitaxial wafer 1a in the first embodiment. The formation of the pixel P by selective diffusion and the manufacture of the electrode are as described above.
By manufacturing the light receiving element 50 using the epitaxial wafer 1a according to the first embodiment, the light receiving element 50 having excellent performance such as low dark current can be obtained efficiently and with high manufacturing yield with high quality crystallinity. Obtainable.

Embodiment 3 Light-Emitting Diode (Semiconductor Element)
FIG. 10 is a diagram showing a light emitting diode (LED) 50e according to Embodiment 3 of the present invention. The LED 50 e has the following InP-based epitaxial laminate on the InP substrate 1.
(N-type InP substrate 1 / n-type InP buffer layer 1000 nm thick / type 2 (InGaAs / GaAsSb) MQW 3 / p-type InP window layer 5 800 nm thick)
A p-side electrode (not shown) is provided on the p-type InP window layer 5 and an n-side electrode (not shown) is provided on the n-type InP substrate 1 so as to be in ohmic contact. As the electrode material, the same material as that of the light receiving element 50 of the second embodiment can be used. By flowing a current between both electrodes, light in the near infrared region having a wavelength of 2 μm to 3 μm can be emitted.
The MQW3 of the epitaxial layer of the LED 50e shown in FIG. 10 grows GaAsSb3a in the MQW3 by the method described in the first or second embodiment. In the case of the light receiving element 50, the MQW3 repeats 250 pairs of InGaAs / GaAsSb, but in the LED 50e, it may be repeated in 2 pairs. The p-type InP window layer 5 is the same as that in the first embodiment except that the p-type InP window layer 5 is not selectively diffused but is doped with a p-type impurity during growth.
By using the growth method of GaAsSb3a in MQW3 in the first embodiment, it is possible to obtain high-quality crystallinity with high efficiency and high manufacturing yield, and to obtain a light-emitting diode 50e with excellent performance.

Example 1 Light Receiving Element (Semiconductor Element)
The light receiving element 50 shown in FIG. 8 was manufactured, and dark current, surface properties, and the like were measured. The surface property was judged by visually observing the surface of the epitaxial wafer. The test bodies are Invention Examples A1 to A6 and Comparative Examples B1 and C1. In Invention Examples A1 to A6, the growth temperature of GaAsSb is in the range of 480 ° C. to 390 ° C., and the growth temperature of InGaAs is the same or higher by 20 ° C. or more. In invention example A4, the growth temperature of InGaAs is 500 ° C., and the growth of GaAsSb is started during the temperature drop to the growth temperature of 450 ° C. of GaAsSb. Therefore, the GaAsSb layer 3a in the MQW of the invention sample A4 has an Sb concentration gradient portion.
Further, the Sb solid thickening rate _x 1 / _{x 2} of the present invention example A1~A6 is in the range of 0.8 to 1.1, in the range 1.20 or less in the range 0.75 to the present invention It is in.
Comparative Example B1 is a test specimen when the growth temperature of GaAsSb in MQW3 is too high at 500 ° C., and the Sb solid phase concentration ratio x ₁ / x ₂ is too low at 0.7. In Comparative Example C1, the growth temperature of the GaAsSb is too low at 380 ° C., but the Sb solid phase concentration ratio x ₁ / x ₂ is 1.0. A specimen having a growth temperature not in the range of 390 ° C. or more and 490 ° C. or less even when the Sb solid phase concentration ratio x ₁ / x ₂ is in the range of 0.75 or more and 1.20 or less was treated as a comparative example. That is, not only the Sb solid phase concentration ratio but also the growth temperature was used as a criterion for determining whether or not the present invention was an example. The characteristics of the light receiving element were comprehensively evaluated for dark current, surface properties, and the like. The evaluation of characteristics was classified into 4 categories: very good (◎), good (○), normal (△), and inferior (×). The results are shown in Table 1.

According to Table 1, all of Examples A1 to A6 of the present invention have normal (Δ) or more characteristics, and none are inferior. In particular, Example A4 of the present invention was very good in both dark current and sensitivity. In addition, Invention Example A4 started GaAsSb growth during a temperature drop from an InGaAs growth temperature of 500 ° C. to 450 ° C., and was able to shorten the manufacturing time. Judging from the results shown in Table 1, when the growth temperature of GaAsSb in MQW is set to 390 ° C. to 490 ° C., the crystallinity is excellent and good performance can be obtained in the light receiving element.
In comparison, Comparative Example B1 could not obtain good characteristics because the growth temperature of GaAsSb in MQW3 was too high at 500 ° C. Further, in Comparative Example C1, the growth temperature of the above GaAsSb was too low at 380 ° C., and thus good characteristics could not be obtained.

Example 2 Light-Emitting Diode (Semiconductor Element)
An LED 50e shown in FIG. 10 was manufactured, and an emission spectrum, surface properties, and the like were measured. The surface property was judged by visually observing the surface of the epitaxial wafer. The test bodies are six bodies of Invention Examples A7 to A10 and Comparative Examples B2 and C2. In Invention Examples A7 to A10, the growth temperature of GaAsSb is in the range of 480 ° C. to 390 ° C., and the growth temperature of InGaAs is the same or higher than 20 ° C. Further, the Sb solid thickening rate _x 1 / _{x 2} of the present invention example A7~A10 is in the range of 0.8 to 1.1, in the range 1.20 or less in the range 0.75 to the present invention It is in. However, as described in Example 1, the distinction between the inventive example and the comparative example was judged by whether or not both the Sb solid phase concentration rate and the growth temperature were satisfied.
Comparative Example B2 is a test specimen when the growth temperature of GaAsSb in MQW3 is too high at 500 ° C. and the Sb solid phase concentration ratio x ₁ / x ₂ is too low at 0.7. In Comparative Example C2, the growth temperature of GaAsSb is too low at 380 ° C., but the Sb solid phase concentration ratio x1 / x2 is 1.0. The characteristics of the light-emitting diode were comprehensively determined in terms of spectrum, surface properties, and the like. The overall judgment of characteristics was classified into 4 categories: very good (◎), good (○), normal (△), and inferior (×). The results are shown in Table 2.

According to Table 2, Examples A7 to A10 of the present invention all have normal (Δ) or more characteristics and none were inferior. From the results shown in Table 2, when the growth temperature of GaAsSb in the MQW is set to 390 ° C. to 490 ° C., the crystallinity is excellent and good performance can be obtained in the light emitting diode.
In contrast, Comparative Example B2 could not obtain good characteristics because the growth temperature of GaAsSb in MQW3 was too high at 500 ° C. In Comparative Example C2, the growth temperature of the above GaAsSb was too low at 380 ° C., and thus good characteristics could not be obtained.

(Example 3-Relationship between Sb mole fraction x _{1 in} group V in the solid phase and Sb mole fraction x _{2 in} group V in the raw material gas)
By changing the growth temperature was determined Sb molar ratio in the solid phase (GaAsSb) and _{(x 1),} the relationship between the Sb mole ratio in the feed gas and _{(x 2).} The results are shown in FIG. In this test, since the growth temperature is 450 ° C. to 525 ° C., which is a relatively high range, the Sb solid phase concentration rate x ₁ / x ₂ is distributed in a range lower than 0.7. FIG. 3 is created based on the result of Example 3.
FIG. 11 or FIG. 3 is information that should be known in advance when the manufacturing method of the present invention is carried out. Without such prior knowledge, the Sb solid phase concentration rate in the present invention cannot be realized within a predetermined range. However, even in this case, _{x 2} in the feed gas, so as to match the _{x 1} in the solid phase (GaAsSb), supplying the raw material gas. By using FIG. 11 or FIG. 3 as prior knowledge, the Sb solid phase concentration rate is in the range of 0.75 to 1.20, or the growth temperature is in the range of 390 ° C. to 490 ° C. A semiconductor element (light receiving element, light emitting element, etc.) having excellent performance can be obtained.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the epitaxial wafer or the like of the present invention, a III-V group compound semiconductor having excellent crystallinity can be obtained while having an Sb-containing layer, and a semiconductor element with good performance can be manufactured. Also, the good crystallinity leads to the fact that abnormal surface defects are less likely to occur, and is effective in improving the manufacturing yield and reducing the manufacturing cost.

  1 InP substrate, 1a epitaxial wafer (intermediate product), 2 buffer layer (InP and / or InGaAs), 3 type II MQW light receiving layer, 3a GaAsSb layer, 3b InGaAs layer, 4 InGaAs layer (diffusion concentration distribution adjusting layer), 5 InP Window layer, 6 p-type region, 11 p-side electrode (pixel electrode), 12 ground electrode (n-side electrode), 12b bump, 15 pn junction, 16 interface between MQW and InGaAs layer, 17 InGaAs layer and InP window layer Interface, 35 AR (antireflection) film, 36 selective diffusion mask pattern, 50 light receiving element (light receiving element array), 60 all organic MOVPE film forming apparatus, 61 infrared temperature monitoring apparatus, 63 reaction chamber, 65 quartz tube, 69 reaction chamber window, 66 substrate table, 66h heater, P pixel.

Claims (17)

A method of manufacturing an epitaxial wafer of a III-V compound semiconductor on a substrate,
A step of alternately growing a first layer containing Sb and a second layer containing no Sb on the substrate by vapor phase growth;
During the growth of the first layer, the Sb mole fraction x ₁ in the group V of the first layer (solid phase) and the Sb mole fraction in the group V of the supplied source gas (gas phase). Epitaxial wafer manufacturing method, characterized in that the substrate temperature is set and the source gas is supplied so that the rate x ₂ satisfies 0.75 ≦ (x ₁ / x ₂ ) ≦ 1.20 .   2. The method of manufacturing an epitaxial wafer according to claim 1, wherein the substrate temperature during the growth of the first layer is set to 390 ° C. or more and 490 ° C. or less.   3. The method of manufacturing an epitaxial wafer according to claim 1, wherein a substrate temperature during the growth of the first layer is set lower than a substrate temperature during the growth of the second layer.   4. The substrate temperature according to claim 1, wherein the substrate temperature during the growth of the second layer is set to be 20 ° C. or more higher than the substrate temperature during the growth of the first layer. 5. Epitaxial wafer manufacturing method.   The growth of the first layer is performed after the growth of the second layer, and the growth of the first layer is performed after the substrate temperature is surely lowered to the temperature during the growth of the first layer. 4. The method for producing an epitaxial wafer according to 4.   5. The method according to claim 3, wherein, after the growth of the second layer, the first layer starts to grow while the temperature is lowered to the substrate temperature at the time of the growth of the first layer. The manufacturing method of the epitaxial wafer of description.   After the growth of the first layer, the second layer is grown by waiting for the substrate temperature to surely rise to the temperature at the time of the growth of the second layer, or during the temperature rise, The method for producing an epitaxial wafer according to claim 3, wherein the second layer starts to grow.   The epitaxial wafer manufacturing method according to claim 1, wherein the first layer is any one of GaAsSb, AlAsSb, and InAsSb. The first layer is GaAs _1-x Sb _x (0 <x ≦ 1), and the second layer is In _y Ga _1-y As (0 <y ≦ 1). Item 9. The method for producing an epitaxial wafer according to any one of Items 1 to 8.   The epitaxial wafer according to claim 1, wherein the substrate is any one of GaAs, GaP, GaSb, InP, InAs, InSb, AlSb, and AlAs. Manufacturing method.   The method for producing an epitaxial wafer according to claim 1, wherein the vapor phase growth method is an all-organic metal vapor phase growth method.   The manufacturing method of a semiconductor element using the epitaxial wafer manufactured by the manufacturing method of any one of Claims 1-11. An III-V compound semiconductor epitaxial wafer having a substrate and an epitaxial layer positioned thereon,
The first layer containing Sb and the second layer not containing Sb are alternately positioned on the substrate,
An epitaxial wafer characterized in that the first layer has an inclined concentration portion where the concentration of Sb increases in a direction away from the substrate.   The epitaxial wafer according to claim 13, wherein the first layer is one of GaAsSb, AlAsSb, and InAsSb. The first layer is GaAs _1-x Sb _x (0 <x ≦ 1), and the second layer is In _y Ga _1-y As (0 <y ≦ 1), The epitaxial wafer according to claim 13 or 14.   The epitaxial wafer according to any one of claims 13 to 15, wherein the substrate is any one of GaAs, GaP, GaSb, InP, InAs, InSb, AlSb, and AlAs. .   A semiconductor device comprising the epitaxial wafer according to claim 13.

Images