KR20070010736A - Nitride semiconductor devices - Google Patents

Abstract

The present invention relates to a nitride semiconductor device, wherein a substrate, an n-type cladding layer formed on the substrate, and a nitride semiconductor layer having different energy bands are sequentially stacked on a portion of the n-type cladding layer. A superlattice layer formed in a multilayer structure, an active layer formed on the superlattice layer, a p-type cladding layer formed on the active layer, a p-type electrode formed on the p-type cladding layer, and The present invention relates to a nitride semiconductor device including an n-type electrode formed on an n-type cladding layer in which the superlattice layer is not formed.

Description

Nitride Semiconductor Devices {NITRIDE SEMICONDUCTOR DEVICE}

1 is a cross-sectional view showing the structure of a nitride semiconductor device (LED) according to the prior art.

2 is a cross-sectional view showing the structure of a nitride semiconductor device (LED) according to an embodiment of the present invention.

3 is a partial cross-sectional view showing a superlattice layer according to a first embodiment of the present invention.

4 is a graph schematically illustrating an example of an energy band gap profile of the superlattice layer of FIG. 3.

5 is a partial cross-sectional view showing a superlattice layer according to a second embodiment of the present invention.

FIG. 6 is a graph schematically showing an example of an energy band gap profile of the superlattice layer of FIG. 5. FIG.

7 is a partial cross-sectional view showing a superlattice layer according to a third embodiment of the present invention

FIG. 8 is a graph schematically showing an example of an energy band gap profile of the superlattice layer of FIG. 7. FIG.

9 is a partial cross-sectional view showing a superlattice layer according to a fourth embodiment of the present invention.

FIG. 10 is a graph schematically showing an example of an energy band gap profile of the superlattice layer of FIG. 9. FIG.

<Explanation of symbols for the main parts of the drawings>

100 substrate 110 buffer layer

120: n-type cladding layer 130: active layer

140: p-type cladding layer 150: transparent conductor layer

160: p-type electrode 170: n-type electrode

200: superlattice layer 210: stress buffer layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device such as a light emitting diode (LED), a laser diode (LD), a light emitting device such as a solar cell, an optical sensor, or a nitride semiconductor device used for electronic devices such as transistors and power devices.

Recently, III-V nitride semiconductors such as GaN have been spotlighted as core materials of light emitting devices such as light emitting diodes (LEDs) or laser diodes (LDs) due to their excellent physical and chemical properties. LEDs or LDs using III-V nitride semiconductor materials are widely used in light emitting devices for obtaining light in the blue or green wavelength band, and these light emitting devices are applied to light sources of various products such as electronic displays and lighting devices. The III-V nitride semiconductor is generally made of a GaN-based material having a composition formula of In _X Al _Y Ga _{1 -X- Y} N (0≤X, 0≤Y, X + Y≤1).

Next, a conventional nitride semiconductor device (LED) using a III-V nitride semiconductor as described above will be described in detail with reference to FIG. 1.

1 is a cross-sectional view schematically showing a structure of a nitride semiconductor device (LED) according to the prior art.

As shown in FIG. 1, an LED device using a nitride semiconductor according to the related art includes a buffer layer 110 made of GaN, an n-type cladding layer 120, and a single quantum well on a sapphire substrate 100 that is a light transmissive substrate. An active layer 130 and a p-type cladding layer 140 of a multi-quantum well (MQW) structure containing InGaN or InGaN having an (SQW) structure are sequentially stacked.

In addition, since some regions of the p-type cladding layer 140 and the active layer 130 are removed by some mesa etching process, some top surfaces of the n-type cladding layer 120 are exposed. In addition, an n-type electrode 170 is formed on the exposed n-type cladding layer 120, and on the p-type cladding layer 160, the transparent conductor layer 150 and the p-type electrode 160 made of ITO or the like. It is formed in this stacked structure.

As described above, the nitride semiconductor device (LED) may adopt a double heterostructure having an active layer 130 having a single quantum well structure or a multi quantum well structure having a well layer made of InGaN.

In particular, in the nitride semiconductor device (LED), the multi-quantum well structure has a large number of mini bands, has high efficiency, and can emit light even at a small current, so that the light emission output is higher than that of the single quantum well structure. Improvement is expected. This discloses an active layer having a multi-quantum well structure consisting of a barrier layer of undoped GaN and a well layer of undoped InGaN in order to improve luminous efficiency and luminous intensity in Japanese Patent Laid-Open No. 10-135514. In addition, a nitride semiconductor device including a cladding layer having a band gap larger than that of the barrier layer of the active layer is disclosed.

However, when the active layer has a multi-quantum well structure, high luminous efficiency and luminous intensity can be obtained, but there is a limit in luminous efficiency and luminous intensity, i.e., light output, for using a nitride semiconductor element as a light source for illumination or an outdoor display. have. In addition, when the active layer has a multi-quantum well structure, the thickness of the entire active layer is higher than that of the single quantum well structure, so that the series resistance in the longitudinal direction is high, and in particular, the operating voltage (V _f ) in the case of an LED element. There is a problem of getting higher.

In addition, since the light emitting device using the nitride semiconductor is generally poor in resistance to electrostatic discharge (ESD), it is necessary to improve the electrostatic discharge characteristics. In particular, the nitride semiconductor LED device or LD device has a problem that can be damaged by the static electricity easily generated in people or things in the process of handling or using the same.

Accordingly, in order to suppress damage of the nitride semiconductor device due to ESD, various studies have recently been conducted. For example, US Pat. No. 6,593,597 discloses a technique for protecting an LED device from ESD by integrating the LED device and the Schottky diode on the same substrate and connecting the LED device and the Schottky diode in parallel. In addition, in order to improve ESD resistance, a method of connecting an LED device in parallel with a Zener diode has been proposed.

However, these methods have the problem of purchasing and assembling a separate zener diode or forming a Schottky junction, thereby increasing the overall manufacturing cost of the device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a nitride semiconductor device that ensures high output characteristics by lowering the operating voltage (V _f ) and improving the electron retention effect and the current dispersion effect.

In addition, an object of the present invention is to provide a nitride semiconductor device that can implement a high ESD resistance without having to provide a separate device for improving the ESD resistance.

In order to achieve the above object, the present invention provides a substrate, an n-type cladding layer formed on the substrate, and a nitride semiconductor layer having different energy bands are sequentially stacked on a portion of the n-type cladding layer. A superlattice layer formed in a multi-layered structure, an active layer formed on the superlattice layer, a p-type cladding layer formed on the active layer, and a p-type electrode formed on the p-type cladding layer And an n-type electrode formed on an n-type cladding layer in which the superlattice layer is not formed.

Further, in the nitride semiconductor device of the present invention, the nitride semiconductor layer constituting the superlattice layer is composed of In _X Al _Y Ga _{1 -X- Y} N (0≤X, 0≤Y, X + Y≤1) composition. Consisting of, it is preferable to have a different energy band by changing the composition ratio of Al and In.

Further, in the nitride semiconductor device of the present invention, the superlattice layer is a first nitride semiconductor layer higher than the energy band of the n-type cladding layer and a second nitride semiconductor layer lower than the energy band of the n-type cladding layer. The superlattice layer is formed by being repeatedly stacked one or more times alternately, or the superlattice layer is formed of a first nitride semiconductor layer lower than an energy band of the n-type cladding layer and a second nitride semiconductor higher than an energy band of the n-type cladding layer. It is preferable that layers are repeatedly laminated one or more times and formed.

Further, in the nitride semiconductor device of the present invention, it is preferable to include at least one nitride semiconductor layer in which an energy band is sequentially increased in either direction between the first nitride semiconductor layer and the second nitride semiconductor layer.

Further, in the nitride semiconductor device of the present invention, it is preferable to further include a transparent conductor layer formed between the p-type cladding layer and the p-type electrode. The transparent conductor layer may further increase the current diffusion effect by increasing the injection area of the current injected through the p-type electrode.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like parts throughout the specification.

A nitride semiconductor device according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, a nitride semiconductor device according to an exemplary embodiment of the present invention will be described in detail with reference to FIG. 2.

2 is a plan view showing the structure of a nitride semiconductor device according to an embodiment of the present invention.

As shown in FIG. 2, a substrate 100 that is light transmissive, a buffer layer 110, an n-type cladding layer 120, a super lattice 200, and an active layer 130 are formed on the substrate 100. ) And the P-type cladding layer 140 are sequentially stacked.

The substrate 100 is a substrate suitable for growing a nitride semiconductor single crystal, and may be a heterogeneous substrate such as a sapphire substrate and a silicon carbonate (SiC) substrate or a homogeneous substrate such as a nitride substrate.

The buffer layer 110 is a layer for improving lattice matching with the sapphire substrate 110 before the n-type cladding layer 120 is grown, and is generally formed of AlN / GaN.

The n-type and p-type cladding layers 120 and 140 and the active layer 130 have an In _X Al _Y Ga _{1- X- Y} N composition formula (where 0 ≦ X, 0 ≦ Y, and X + Y ≦ 1). It may be made of a semiconductor material having. More specifically, the n-type cladding layer 120 may be formed of a GaN layer or a GaN / AlGaN layer doped with n-type conductive impurities, for example, Si, Ge, Sn, etc. Is used, and preferably Si is mainly used. In addition, the p-type cladding layer 140 may be formed of a GaN layer or a GaN / AlGaN layer doped with a p-type conductive impurity. For example, Mg, Zn, Be, or the like may be used as the p-type conductive impurity. Preferably, Mg is mainly used. The active layer 130 may be formed of an InGaN / GaN layer having a multi-quantum well structure.

Particularly, in the present invention, a superlattice layer 200 having a multilayer structure in which nitride semiconductor layers having different energy bands are sequentially stacked is formed at an interface between the n-type cladding layer 120 and the active layer 130. . This is to enhance the cladding effect and the current diffusion effect of the n-type cladding layer 120 and to enhance the resistance of the electrostatic discharge (ESD) characteristics.

Next, specific types of the superlattice layer 200 having a multilayer structure in which nitride semiconductor layers having different energy bands are sequentially stacked will be described with reference to FIGS. 3 to 10.

Example  One

The superlattice layer of the nitride semiconductor device according to the first embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

3 is a partial cross-sectional view showing a superlattice layer according to a first embodiment of the present invention, and FIG. 4 is a graph schematically showing an example of an energy bandgap profile of the superlattice layer of FIG. 3.

Referring to FIG. 3, a nitride semiconductor layer having different energy bands on the n-type cladding layer 120, for example, a first energy band having a higher energy band based on the energy band of the n-type cladding layer 120. A superlattice layer is formed in which the nitride semiconductor layer 200a and the second nitride semiconductor layer 200b having a lower energy band are alternately repeatedly stacked a plurality of times. In this case, the first and the second nitride semiconductor layer (200a, 200b) is a semiconductor material having an In _X Al _Y Ga _{1-X- Y} N composition formula (where 0≤X, 0≤Y, X + Y≤1) It consists of and has different energy bands through different composition ratios of In and Al. In the present embodiment, GaN is used as the n-type cladding layer 120, AlGaN is used as the first nitride semiconductor layer 200a, and InGaN is used as the second nitride semiconductor layer 200b.

Accordingly, the superlattice layer 200 according to the embodiment of the present invention has different energy bands of the first nitride semiconductor layer 200a and the second nitride semiconductor layer 200b, that is, as shown in FIG. 5. The discontinuity of the energy band in which the energy band changes rapidly at the interface between the first nitride semiconductor layer 200a and the second nitride semiconductor layer 200b forms a two-dimensional electron gas layer (not shown) at the interface.

Accordingly, when voltage is applied, a tunneling phenomenon occurs through the two-dimensional electron gas layer through n ⁺ -p ⁺ junctions, thereby improving the cladding effect of the n-type cladding layer 120 and ensuring high carrier mobility to spread current. The effect can be improved. As such, when the current diffusion effect in the superlattice layer 200 is improved, the operating voltage V _f is lowered and the light emission efficiency is also improved due to the increase in the light emission area, thereby realizing a nitride semiconductor device that secures light output. Can be.

In addition, the second nitride semiconductor layer 200b made of InGaN of the superlattice layer 200 is interposed between the n-type cladding layer 120 made of GaN and the active layer 130 made of AlGaN to have a relatively high dielectric constant. Therefore, the superlattice layer 200 may serve as a kind of capacitor. Accordingly, the superlattice layer 200 can protect the nitride semiconductor device from sudden surge voltage or electrostatic phenomenon, thereby improving the ESD resistance of the device.

Example  2

5 and 6, a second embodiment of the present invention will be described. However, the description of the same parts as those of the first embodiment of the configuration of the second embodiment will be omitted, and only the configuration that is different from the second embodiment will be described in detail.

5 is a partial cross-sectional view showing a superlattice layer according to a second embodiment of the present invention, and FIG. 6 is a graph schematically showing an example of an energy bandgap profile of the superlattice layer of FIG. 5.

5 and 6, the superlattice layer 200 according to the second embodiment has the same configuration as that of the superlattice layer 200 according to the first embodiment, except that the n-type cladding is provided. The energy band of the n-type cladding layer 120 other than the first nitride semiconductor layer 200a having the energy band higher than that of the n-type cladding layer 120 is formed on the lowermost layer of the nitride semiconductor layer formed on the layer 120. It differs from the first embodiment only in that it is a second nitride semiconductor 200b having a lower energy band.

That is, in the first embodiment, the first nitride semiconductor layer higher than the energy band of the n-type cladding layer and the second nitride semiconductor layer lower than the energy band of the n-type cladding layer are alternately used as the superlattice layer. The above-described embodiment is repeatedly stacked and formed, and the second embodiment has the superlattice layer having a higher energy band than the first nitride semiconductor layer and the n-type cladding layer, which are lower than the energy band of the n-type cladding layer. It illustrates that the second nitride semiconductor layer is formed by alternately stacking one or more times.

Thus, this second embodiment can achieve the same effects and effects as in the first embodiment.

Example  3

Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. 7 and 8. However, the description of the same parts as those of the first embodiment of the configuration of the third embodiment will be omitted, and only the configuration that is different from the third embodiment will be described in detail.

7 is a partial cross-sectional view showing a superlattice layer according to a third embodiment of the present invention, and FIG. 8 is a graph schematically showing an example of an energy bandgap profile of the superlattice layer of FIG. 7.

As shown in FIGS. 7 and 8, the superlattice layer 200 according to the third embodiment has the same structure as that of the superlattice layer 200 according to the first embodiment, except that the first nitride is used. A first buffer layer 300 may further include a stress buffer layer 300, which is one or more layers of a nitride semiconductor layer in which an energy band is sequentially increased between the semiconductor layer 200a and the second nitride semiconductor layer 200b. It differs from an Example. In this case, the stress buffer layer 300 is made of a semiconductor material having an In _X Al _Y Ga _{1 -X- Y} N composition formula (where 0≤X, 0≤Y, X + Y≤1), and In and Al The ratio of the energy band gap between the first nitride semiconductor layer 200a and the second nitride semiconductor layer 200b is controlled through different composition ratios.

Accordingly, the third embodiment not only obtains the same functions and effects as in the first embodiment, but also the stress buffer layer 300 formed between the first nitride semiconductor layer 200a and the second nitride semiconductor layer 200b. By buffering a rapidly changing energy bandgap at the interface between the first nitride semiconductor layer 200a and the second nitride semiconductor layer 200b, there is an advantage that the characteristics of the device can be more stably maintained.

On the other hand, although not shown, such a stress buffer layer 300 can be applied to the superlattice layer described in the second embodiment of the present invention.

Example  4

Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS. 9 and 10. However, the description of the same parts as those of the third embodiment in the configuration of the fourth embodiment will be omitted, and only the configuration that is different from the third embodiment will be described in detail.

9 is a partial cross-sectional view showing a superlattice layer according to a fourth embodiment of the present invention, and FIG. 10 is a graph schematically showing an example of an energy bandgap profile of the superlattice layer of FIG. 9.

9 and 10, the superlattice layer according to the fourth embodiment has the same structure as that of the superlattice layer according to the third embodiment, except that the first nitride semiconductor is used in the fourth embodiment. A three-layer structure in which the layer 200a, the second nitride semiconductor layer 200b, and the first nitride semiconductor layer 200a are sequentially stacked is repeatedly stacked a plurality of times in one cycle, and the first nitride semiconductor layer 200a. Stress), which is one or more layers of nitride semiconductor layers in which an energy band sequentially increases in either direction between the second nitride semiconductor layer 200b and between the second nitride semiconductor layer 200b and the first nitride semiconductor layer 200b. (stress) Different from the third embodiment only in that the buffer layer 300 is further included.

Therefore, the fourth embodiment has an advantage that the same operation and effect as in the third embodiment can be obtained.

In addition, the nitride semiconductor device according to the present invention includes a plurality of mesas formed by etching the p-type cladding layer 140 and the active layer 130 to expose a portion of the upper surface of the n-type cladding layer 120, and the plurality of mesas. The n-type electrode 170 formed on the exposed n-type cladding layer 120 on the mesa, and the transparent conductor layer 150 and the transparent conductor layer formed on the p-type cladding layer 140 to diffuse current. A p-type electrode 160 that serves as a reflective metal and a bonding metal on 150 is included.

In the light emitting structure of the present embodiment, the transparent conductor layer 150 is a layer for improving the current diffusion effect by increasing the current injection area, Indium Tin Oxide (ITO), Tin Oxide (TO), Indium Zinc (IZO) Oxide), ITZO (Indium Tin Zinc Oxide) and TCO (Transparent Conductive Oxide) is preferably made of any one film selected from the group consisting of.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

As described above, the present invention provides a multi-layered superlattice layer formed by sequentially stacking nitride semiconductor layers having different energy bands between an n-type cladding layer and an active layer, thereby cladding the n-type cladding layer. The effect and current spreading effect can be improved.

As described above, the present invention reduces the operating voltage (V _f ) due to the improvement of the current diffusion effect to improve the luminous efficiency, thereby realizing a nitride semiconductor device that can obtain a high light output.

In addition, in the present invention, since a structure in which nitride semiconductor layers having different energy bands of the superlattice layer are sequentially stacked serves as a kind of capacitor, ESD resistance is not required to include a separate device for improving ESD resistance. The nitride semiconductor device having high reliability can be realized by improving the efficiency.

Claims (6)

Board; An n-type cladding layer formed on the substrate; A superlattice layer having a multilayer structure in which nitride semiconductor layers having different energy bands are sequentially stacked on a portion of the n-type cladding layer; An active layer formed on the superlattice layer; A p-type cladding layer formed on the active layer; A p-type electrode formed on the p-type cladding layer; And And an n-type electrode formed on the n-type cladding layer in which the superlattice layer is not formed. The method of claim 1, The nitride semiconductor layer having different energy bands constituting the superlattice layer is composed of In _X Al _Y Ga _{1 -X- Y} N (0≤X, 0≤Y, X + Y≤1) composition, and Al A nitride semiconductor device, characterized in that formed by varying the composition ratio of and In. The method of claim 1, The superlattice layer is formed by alternately stacking the first nitride semiconductor layer higher than the energy band of the n-type cladding layer and the second nitride semiconductor layer lower than the energy band of the n-type cladding layer one or more times in turn. A nitride semiconductor element. The method of claim 1, The superlattice layer is formed by alternately stacking the first nitride semiconductor layer lower than the energy band of the n-type cladding layer and the second nitride semiconductor layer higher than the energy band of the n-type cladding layer one or more times. A nitride semiconductor element. The method according to claim 3 or 4, A nitride semiconductor device comprising at least one nitride semiconductor layer in which an energy band sequentially increases in either direction between the first nitride semiconductor layer and the second nitride semiconductor layer. The method of claim 1, And a transparent conductor layer formed between the p-type cladding layer and the p-type electrode.

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