KR100906972B1 - Nitride based light emitting device - Google Patents

Abstract

A nitride based light emitting device is disclosed. The light emitting element is interposed between a substrate, an n-type nitride semiconductor layer formed on the substrate, a p-type nitride semiconductor layer formed on the n-type nitride semiconductor layer, and the n-type nitride semiconductor layer and the p-type nitride semiconductor layer. It includes an active layer having a quantum well layer and a quantum barrier layer. On the other hand, the first strain reducing layer consisting of In _z Ga _{1 - z} N (0.1 <z <1) having a different In content between the n-type nitride semiconductor layer and the active layer, and In _{z '} Ga _{1 - z'} A second strain reducing layer made of N (0 <z '<0.5) is formed at least once and the In content of the first strain reducing layer is smaller than the In content of the quantum well layer, and It is characterized by being larger than the In content.

Strain Reduction Layer, Internal Quantum Efficiency, Quantum Well Layer, Quantum Barrier Layer, Nitride

Description

Nitride-based light emitting device {NITRIDE BASED LIGHT EMITTING DEVICE}

The present invention relates to a nitride-based light emitting device, and more particularly, by inserting a strain reducing layer before growing the active layer, to reduce the lattice mismatch generated between the n-type nitride semiconductor layer and the active layer, to the adjacent quantum well layer It has a strain relaxation effect, thereby improving indium incorporation, thereby improving internal quantum efficiency, and reducing strain that generates a piezoelectric field in the active layer, thereby improving the withstand voltage characteristics. An improved high efficiency nitride based light emitting device is disclosed.

In general, nitride-based semiconductors are widely used in blue / green light emitting diodes or laser diodes as light sources for full color displays, traffic lights, general lighting and optical communication devices. The nitride-based light emitting device includes an InGaN-based multi-quantum well structured active layer disposed between n-type and p-type nitride semiconductor layers, and generates and emits light based on the principle of recombination of electrons and holes in the active layer. While light emitting devices in the blue and ultraviolet regions using nitrides have brought a lot of development, there have been many difficulties in implementing light emitting devices in the long wavelength region such as green and red. Due to the 11% lattice mismatch between GaN and InN, strong strain occurs at the interface between the quantum well and the quantum barrier in the InGaN series multi-quantum well structure. This strain distribution is closely related to the spinodal decomposition process in the quantum wells. Therefore, in the case of the ordinary InGaN-based multi-quantum well structure, injecting more than 15% of indium into the quantum well causes strong composition fluctuation or indium-rich nano clusters in which a large amount of indium is aggregated. In other words, large blue shifts are blocked by blocking the paths of carriers injected due to the strong quantum confined stark effect (QCSE) generated near the interface between the quantum well and the quantum barrier due to lattice mismatch between GaN and InN. shift) occurs. On the other hand, dangling bonds are formed on the surface to increase dislocation density on subsequently grown GaN crystals. These phenomena immediately lead to a decrease in internal quantum efficiency.

1 is an energy band diagram of a conventional nitride based light emitting device. Conventionally, it can be seen that the n-type nitride semiconductor layer and the active layer are continuously grown. This continuous growth not only greatly deteriorates the crystallinity of the active layer due to the strain due to the difference in lattice constant, but also increases the distance between the wave functions due to the influence of the piezoelectric field on the active layer, reducing the probability of recombination of electrons and holes. This results in deterioration of the constant voltage characteristics. This acts as a major variable to reduce the luminous efficiency of the device. In addition, in order to realize light emission in the long wavelength region, the growth temperature of the quantum well should be excessively lowered in preparation for the growth temperature of both wells for implementing blue color, and the indium segregation generated at this time makes it possible to manufacture high quality devices. Becomes difficult. Therefore, the technique of increasing indium incorporation must be an important variable constituting the light emitting device of the green-yellow-orange region using the nitride system.

The present invention is to solve the above-mentioned problems of the prior art, by using an strain reducing layer to improve the indium incorporation (indium incorporation) in the adjacent quantum wells to improve the internal quantum efficiency (quantum efficiency) of the nitride-based light emitting device In addition, to provide a high-efficiency nitride-based light emitting device that can improve the withstand voltage characteristics by reducing the strain problem that generates the piezoelectric field in the active layer, an object thereof.

The present invention for achieving the above object,

Board;

An n-type nitride semiconductor layer formed on the substrate;

A p-type nitride semiconductor layer formed on the n-type nitride semiconductor layer; And

A nitride-based light emitting device comprising: an active layer interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer and having a quantum well layer and a quantum barrier layer.

A first strain reducing layer made of In _z Ga _1-z N (0.1 <z <1) having a different In content between the n-type nitride semiconductor layer and the active layer, and In _{z '} Ga _{1 - z'} N ( A second strain reduction layer made of 0 <z '<0.5) is formed at least once, and the In content of the first strain reduction layer is smaller than the In content of the quantum well layer, and the In content of the quantum barrier layer. It is characterized by being larger.

In this case, the In content of the first strain reduction layer is preferably larger than the In content of the second strain reduction layer, wherein the first strain reduction layer corresponds to 1/4 to 1/2 of the thickness of the adjacent quantum well layer. It is desirable to have a thickness.

In addition, the energy band gap of the second strain reducing layer is preferably the same as the energy band gap of the quantum barrier layer, and the second strain reducing layer corresponds to 1/2 to 3/4 of the thickness of the adjacent quantum barrier layer. It is desirable to have a thickness to be.

According to one embodiment of the present invention, at least one of the first strain reducing layer and the second strain reducing layer may be doped with n-type impurities, wherein the first strain reducing layer and the second strain reducing layer The n-type impurity concentration may increase or decrease as it approaches the active layer.

Further, the first strain reducing layer and the second strain reducing layer are more preferably formed once or twice.

In addition, the active layer may be a multi-quantum well structure formed by repeating the quantum well layer and the quantum barrier layer at least twice.

As described above, according to the present invention, the strain reducing layer improves indium incorporation in adjacent quantum wells through strong strain relaxation, and thus not only high quality blue region nitride based light emitting devices By implementing a light emitting device having a long wavelength region such as green-red light, it is possible to greatly improve the constant voltage characteristic by reducing the strain problem of generating a piezoelectric field in the active layer.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail.

2 is a cross-sectional view of a nitride based light emitting device according to an exemplary embodiment of the present invention, and FIG. 3 is an enlarged partial view of the n-type nitride semiconductor layer and the active layer of FIG. 2.

First, referring to FIG. 2, in the nitride-based light emitting device, an n-type nitride semiconductor layer 2-3 and an active layer 2 are sequentially formed after forming a buffer layer 2-2 on the substrate 2-1. -4) and p-type nitride semiconductor layers 2-5. An n-layer electrode 2-6 is disposed on the exposed upper surface of the n-type nitride semiconductor layer 2-3, and a p-layer electrode 2-7 is disposed on the exposed upper surface of the p-type nitride semiconductor layer 2-5. Each is provided.

In the nitride-based light emitting device according to the present invention, the first strain reducing layer 2-b and the second strain reducing layer having different compositions between the n-type nitride semiconductor layer 2-3 and the active layer 2-4. (2-c) includes a strain reducing layer (2-a) formed at least once. In this case, preferably, the first strain reducing layer and the second strain reducing layer are repeatedly formed one or two times.

The strain reducing layer (2-a) employed in this embodiment is suitable for improving indium incorporation due to the first strain reducing layer and the second strain reducing layer to mitigate lateral strain. It can be configured to have an energy band gap.

More specifically, referring to FIG. 3, the energy band gap of the first strain reducing layer 2-b has a larger value than the energy band gap of the adjacent quantum well layer 3-1 and the quantum barrier. It has a smaller value than the energy bandgap of layer 3-2, thereby achieving the object of the present invention. Preferably, the thickness of the first strain reducing layer has a thickness corresponding to 1/4 to 1/2 of the adjacent quantum well layer 3-1.

The energy band gap of the second strain reducing layer 2-c is preferably about the same as the energy band gap of the adjacent quantum barrier layer 3-2, and more preferably completely the same. The thickness of the second strain reducing layer preferably has a thickness corresponding to 1/2 to 3/4 of the adjacent quantum barrier layer 3-2.

Therefore, the strain reducing layer 2-a disposed between the n-type nitride semiconductor layer 2-3 and the active layer 2-4 has a large size of InGaN atoms in the n-type nitride semiconductor layer 2-3. The internal quantum efficiency is improved by generating a tensile strain in the quantum barrier layer so that it can be more easily settled, thereby improving the indium incorporation of adjacent quantum well layers 3-1. At the same time, the effect of the piezoelectric field effect can be reduced to suppress the increase in the wave function distance between the electron and the hole, and thus the width of the wavelength change due to the increase of the operation current can be reduced.

At least one of the first strain reducing layer and the second strain reducing layer of the strain reducing layer used in the present invention may be doped with n-type impurities. In addition, the n-type impurity concentration of the first strain reducing layer or the second strain reducing layer may be configured to be gradually changed. For example, the n-type impurity concentration of the first strain reducing layer or the second strain reducing layer may increase or decrease as it approaches the active layer. In this case, the impurity concentration of the n-type nitride semiconductor layer may be higher or lower than the impurity concentration of the low indium content layer adjacent thereto.

In addition, according to an embodiment of the present invention, the In content of the first strain reducing layer is more preferably greater than the In content of the second strain reducing layer.

In a specific embodiment of the invention, the active layer comprises at least two quantum well layers of In _x Ga _{1- x} N (0.1 <x <1) and a quantum barrier layer of In _y Ga _{1- y} N (0 <y <0.5). It may be a multi-quantum well structure formed repeatedly. The In content x of the quantum well layer has a larger value than the In content y of the quantum barrier layer.

4 shows an energy band diagram of a strain reducing layer and an active layer in a nitride based light emitting device having an InGaN series multi-quantum well structure.

The energy band gap Eg of the first strain reducing layer is designed to be larger than the energy band gap Eg1 of the adjacent quantum well layer but smaller than the energy band gap Eg1 'of the quantum barrier layer. The thickness has a thickness corresponding to 1/4 to 1/2 of the adjacent quantum well layer.

The energy band gap Eg 'of the second strain reducing layer is substantially the same as the energy band gap Eg1' of the adjacent quantum barrier layer, and the thickness corresponds to 1/2 to 3/4 of the adjacent quantum barrier layer. Has a thickness.

A first embodiment of the nitride based light emitting device according to the present invention is as follows.

Growth methods of nitride-based light emitting devices include metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE; Molecular Beam Epitaxy), and hydride vapor phase growth (HVPE). Various methods can be used, and the present embodiment uses organometallic chemical vapor deposition (MOCVD).

2, a buffer layer 2-2, an n-type nitride semiconductor layer 2-3, a strain reducing layer 2-a, an active layer 2-4, and a p-type on the substrate 2-1. The nitride semiconductor layer 2-5 is formed sequentially.

The substrate refers to a wafer for fabricating a nitride-based light emitting device, and uses a heterogeneous substrate such as sapphire (Al 2 O 3), silicon carbide (SiC), silicon (Si), gallium arsenide (GaAs), or the like. At least one of the substrates is used. In this embodiment, a crystal growth substrate made of sapphire is used.

The buffer layer 2-2 is to reduce lattice mismatch between the substrate and subsequent layers during crystal growth on the substrate, and may include InAlGaN series, SiC, or ZnO. In this embodiment, a buffer layer composed of InAlGaN series is used.

The n-type nitride semiconductor layer 2-3 is a layer in which electrons are generated, and an n-type nitride semiconductor layer doped with Si is used. In this embodiment, an impurity concentration of 1 × 10 ¹⁷ / cm 3 to 5 × 10 ¹⁹ / cm 3 is used as an n-type nitride semiconductor layer by using an inert gas such as SiH 4 or Si 2 H 4, or by using an MO source such as DTBSi. It is possible to form an n-type nitride semiconductor layer having a thickness of 1.0 ~ 5.0㎛.

Then, as shown in the present invention, the strain consisting of the first strain reducing layer (2-b) and the second strain reducing layer (2-c) consisting of In _z Ga _{1 -z} N (0.1 <z <1) The reduction layer 2-a may be formed by repeating one or more times, preferably one or two times. In this case, the In content of the first strain reducing layer is increased by about 30 ° C. (blue luminescent region) to 100 ° C. (green luminescent region or more) relative to the growth temperature of the adjacent quantum well layer 3-1. In this method, the method is larger than the band gap Eg1 of the adjacent quantum well layer 3-1 but smaller than the band gap Eg1 'of the quantum barrier layer 3-2. It is designed. In this case, the thickness of the first strain reducing layer may have a thickness corresponding to 1/4 to 1/2 of the thickness of the adjacent quantum well layer 3-1, and may have a thickness of, for example, 1 to 3 nm. As a result, the first strain reducing layer 2-b is designed to emit light in the UV region. The energy band gap Eg 'of the second strain reducing layer 2-c is substantially the same as the band gap Eg1' of the adjacent quantum barrier layer 3-2, and preferably becomes the same. In addition, the thickness of the second strain reducing layer may be formed to have a thickness corresponding to 1/2 to 3/4 of the adjacent quantum barrier layer (3-2), for example, a thickness of 5 ~ 20nm Can have

Next, the active layer 2-4 is formed. The active layer 2-4 includes an In _x Ga1 _1-x N (0.1 <x <1) quantum well layer 3-1 and an In _y Ga _{1- y} N (0 <y <0.5) quantum barrier layer (3). -2) formed a multi-quantum well structure consisting of two or more and ten or fewer repetitions. More preferably, each quantum well layer 3-1 is formed with a thickness of 1-4 nm and In (0.1 <x <0.4), and each quantum barrier layer 3-2 has a thickness of 5-20 nm and an In content ( 0 <y <0.2).

Next, a p-type nitride semiconductor layer 2-5 doped with Mg is formed on the active layer 2-4. Here, trimethylgallium (TMGa) or triethylgallium (TEGa) may be used as a source gas for Ga, and ammonia (NH 3), dimethylhydrazine (DMHy) may be used as a source gas for N, and a source for Mg. The gas may be CP2Mg or DMZn. Using this, a p-type nitride semiconductor layer 2-5 having an Mg doping concentration of 3 to 8 x 10 ¹⁷ / cm 3 and a thickness of 1 to 3 mu m is formed. After proper mesa etching, the n-layer electrode 2-6 is exposed on the exposed upper surface of the n-type nitride semiconductor layer 2-3, and the p-layer is disposed on the exposed upper surface of the p-type nitride semiconductor layer 2-5. The electrodes 2-7 are formed, respectively.

(Comparative Example)

A nitride light emitting device was manufactured under the same condition as the above-described embodiment, except for the strain reducing layer employed in the present invention.

The nitride light emitting devices obtained in the above-mentioned Examples and Comparative Examples were confirmed by changing the wavelength of emitted light while gradually increasing the current from 0 to 50 mA and the results are shown in the graph of FIG. 5.

As shown in FIG. 5, when the current increases from 10 mA to 50 mA, in the case of the comparative example, it can be seen that the emission light wavelength is lowered by about 20 nm from 517 nm to 498 nm. In contrast, in the case of the embodiment according to the present invention, only a wavelength change of about 8 nm was observed in the same current increase range from 526 nm to 518 nm. The following two things can be considered as the degree of change of wavelength according to the increase of the current. One obtained emission wavelengths of 517 nm in the comparative example at the same quantum well growth temperature, while the emission wavelength of 526 nm was increased by about 10 nm in the example. This is because the strain reducing layer improves indium incorporation in adjacent quantum wells, and thus the wavelength of emitted light changes toward the longer wavelength. Next, due to the distance difference between the wave function of the electron and the electromagnet by the piezoelectric field, the distance difference of the wave function is large in the comparative example, but in the present invention is greatly reduced and the influence by the piezoelectric field is very weak. Can be.

As described above, the strain reducing layer according to the present invention improves the indium corporation of the adjacent quantum well layers, thereby improving not only high-quality blue light emitting devices having improved internal quantum efficiency, but also light emitting devices having long wavelength regions. At the same time, it is possible to reduce the strain problem of generating the piezoelectric field in the active layer, thereby greatly improving characteristics such as improvement of the constant voltage.

In the above embodiment, a nitride-based light emitting device has been described as an example, but it is apparent to those skilled in the art that the present invention can be advantageously employed in other nitride-based optical devices having a similar structure, such as semiconductor laser devices.

As described above, the present invention has been described in detail through preferred embodiments, but the scope of the present invention is not limited to the specific embodiments, and should be interpreted by the appended claims. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

1 is an energy band diagram of a conventional nitride based light emitting device.

2 is a cross-sectional view of a nitride-based light emitting device according to the present invention.

3 is a partial detailed view of a nitride-based light emitting device according to the present invention.

4 is an energy band diagram of a nitride-based light emitting device according to the present invention.

5 is a graph showing the wavelength change of the emitted light with respect to the current increase of the nitride-based light emitting device and the conventional nitride-based light emitting device according to the present invention.

<Code Description of Main Parts of Drawing>

2-1: substrate, 2-2: buffer layer

2-3: n-type nitride semiconductor layer

2-4: active layer

2-5: p-type nitride semiconductor layer

2-6: n-layer electrode, 2-7: p-layer electrode

2-a: strain reducing layer

2-b: first strain reducing layer

2-c: second strain reducing layer

3-1: quantum well layer, 3-2: quantum barrier layer

Claims (9)

Board; An n-type nitride semiconductor layer formed on the substrate; A p-type nitride semiconductor layer formed on the n-type nitride semiconductor layer; And A nitride-based light emitting device comprising: an active layer interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer and having a quantum well layer and a quantum barrier layer. A first strain reducing layer made of In _z Ga _1-z N (0.1 <z <1) having a different In content between the n-type nitride semiconductor layer and the active layer, and In _{z '} Ga _1-z' N ( A second strain reduction layer made of 0 <z '<0.5) is formed at least once, and the In content of the first strain reduction layer is smaller than the In content of the quantum well layer, and the In content of the quantum barrier layer. A nitride-based light emitting device, characterized in that greater than, greater than the In content of the second strain reducing layer. delete The method of claim 1, The first strain reducing layer has a thickness corresponding to 1/4 to 1/2 of the thickness of the adjacent quantum well layer. The method of claim 1, The energy band gap of the second strain reducing layer is the same as the energy band gap of the quantum barrier layer. The method of claim 1, The second strain reducing layer has a thickness corresponding to 1/2 to 3/4 of the thickness of the adjacent quantum barrier layer. The method according to any one of claims 1 and 3 to 5, And at least one of the first strain reducing layer and the second strain reducing layer is doped with n-type impurities. The method of claim 6, The n-type impurity concentration of the first strain reducing layer or the second strain reducing layer increases or decreases closer to the active layer. The method of claim 1, The first strain reducing layer and the second strain reducing layer is nitride-based light emitting device, characterized in that formed repeatedly one or two times. The method of claim 1, The active layer is a nitride-based light emitting device, characterized in that the quantum well layer and the quantum barrier layer is a multi-quantum well structure formed by repeating at least twice.

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