KR20100077264A - Light emitting diode having indium nitride - Google Patents

Abstract

PURPOSE: A light emitting diode is provided to improve the crystalline of a p-type nitride semiconductor layer by choosing a p-type InN/InGaN multilayer. CONSTITUTION: An active area(29) of a multiple quantum well structure is formed between a n-type nitride semiconductor layer(27) and a p-type nitride semiconductor layer(33). The active area comprises an InGaN quantum-well layer. A p-type multilayer(31) is formed between the p-type nitride semiconductor layer and the active area. In the p-type multilayer, an InN layer and an InxGa1-xN layer are sequentially laminated, at least 2 times. The p-type impurity density of the p-type InN layer is higher than the p-type impurity density of the InxGa1-xN layer.

Description

Light emitting diode containing indium nitride {LIGHT EMITTING DIODE HAVING INDIUM NITRIDE}

The present invention relates to a light emitting diode, and more particularly to a light emitting diode comprising indium nitride.

In general, nitride-based semiconductors are widely used in ultraviolet, 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 active region of an InGaN-based multi-quantum well structure located between n-type and p-type nitride semiconductor layers, and generates light based on the recombination of electrons and holes in the quantum well layer in the active region. To release.

In such a conventional nitride compound semiconductor, the electron mobility is known to be 10 times or more larger than the mobility of the hole. Therefore, the electrons move in the multi-quantum well structure faster than the holes to reach the p-type nitride semiconductor layer, and these electrons can flow into the p-type semiconductor layer without recombination with the holes. An electron blocking layer (EBL) is commonly used to prevent this and to trap electrons in the multi-quantum well structure.

However, since the electron blocking layer has a relatively wide energy band gap, it prevents holes from flowing into the multi-quantum well structure, thereby increasing the forward voltage. Moreover, the electron blocking layer is formed of AlGaN grown at a relatively high temperature. Therefore, a problem arises in that the InGaN layer formed as the upper layer of the active region is dissociated at the AlGaN growth temperature. Dissociation of the InGaN layer degrades the quality of the active region and increases non-luminescent recombination.

On the other hand, the p-type nitride semiconductor layer usually consists of a GaN layer doped with Mg. However, there is a limit in increasing the hole concentration by doping Mg in the GaN layer, and the hole concentration has not yet exceeded 10 ¹⁸ orders. Accordingly, the resistivity of the p-type nitride semiconductor layer is relatively high and there is a limit to lowering the forward voltage.

The problem to be solved by the present invention is to provide a light emitting diode that can be smoothly introduced into the active area.

Another object of the present invention is to provide a light emitting diode that can increase the hole concentration flowing into the active region.

Another object of the present invention is to provide a light emitting diode that can lower the forward voltage.

In order to solve the above problems, a light emitting diode according to embodiments of the present invention is interposed between an n-type nitride semiconductor layer, a p-type nitride semiconductor layer, the n-type nitride semiconductor layer and the p-type nitride semiconductor layer and InGaN quantum well An active region having a multi-quantum well structure including a layer, and a p-type multilayer film interposed between the p-type nitride semiconductor layer and the active region. Meanwhile, the multilayer film has a structure in which an InN layer and an In _x Ga _1-x N (0 ≦ x <1) layer are alternately stacked at least twice.

By adopting the multilayer film structure, the crystallinity of the p-type nitride semiconductor layer formed thereon can be improved. The crystallinity of the p-type nitride semiconductor layer is related to the resistivity of the p-type nitride semiconductor layer, and as the crystallinity is improved, the specific resistance can be lowered and the thickness of the p-type nitride semiconductor layer can be lowered. In addition, by adopting a multilayer film of an InN layer and an InGaN layer having a relatively narrow band gap, the energy barrier for the hole such as the conventional EBL can be eliminated, and the hole can be smoothly introduced into the active region. Accordingly, the forward voltage of the light emitting diode can be reduced.

The multilayer film may include a p-type InN layer doped with p-type impurities. Since the InN layer has a narrower bandgap of 0.7 eV than that of the GaN layer, the ionization energy of the p-type impurity can be lowered, and thus the hole concentration due to impurity doping can be relatively increased compared to the GaN layer. The hole concentration in the InG layer can be further increased with improving the crystallinity of the InN layer.

Therefore, the hole concentration can be increased in the multilayer film, so that the inflow of holes into the active region is more smoothly performed.

The In _x Ga _1-x N (0 ≦ x <1) layer is also doped with p-type impurities. However, since the hole concentration can be further increased in the InN layer, the p-type impurity concentration of the p-type InN layer is higher than the p-type impurity concentration of the In _x Ga _1-x N (0≤x <1) layer. desirable.

The multilayer film may contact the active region. In embodiments of the present invention, the conventional electron blocking layer is excluded. The active region of the quantum well structure may have a stacked structure of an InGaN quantum well layer and an InGaN barrier layer. In this case, the multilayer film may be in contact with an InGaN quantum well layer or an InGaN barrier layer. By combining a multi-quantum well structure in which an InGaN quantum well layer and an InGaN barrier layer are alternately stacked, and the InN / In _x Ga _1-x N multilayer, the holes may be smoothly introduced into the multi-quantum well structure.

On the other hand, the necessity of the electron blocking layer according to the mobility of the electrons can be removed through the thickness control of the barrier layer in the quantum well structure, the bandgap control of the quantum barrier layers, doping techniques and the like. For example, movement of electrons may be alleviated by disposing a relatively thick barrier layer close to the n-type nitride semiconductor layer. In addition, by disposing a barrier layer doped with a p-type impurity or a barrier layer having a relatively wide band gap in the quantum well structure, the movement of electrons can be alleviated. Therefore, even if the electron blocking layer is not used, the emission recombination rate of the electrons can be prevented from being reduced.

On the other hand, when the multilayer film is in contact with the InGaN barrier layer, it is preferable that the InGaN barrier layer is in contact with the multilayer film has a relatively narrow energy band gap compared to other barrier layers. Accordingly, a hole can be smoothly introduced into the quantum well layer through the barrier layer.

Meanwhile, the InN layer and the In _x Ga _1-x N (0 ≦ x <1) layer may have a thickness of 5 μs to 200 μs. In addition, the multilayer film may have a superlattice structure. Therefore, the crystallinity of the multilayer film can be further improved, and the crystallinity of the p-type nitride semiconductor layer can be further improved.

The In _x Ga _1-x N (0 ≦ x <1) layers in the multilayer may all have the same In content, but the present invention is not limited thereto and may include more In as closer to the active region. This change in In content forms a composition gradient towards the active area to help the holes enter the active area.

The present invention also includes an InN layer on an active region of a multi-quantum well structure comprising an InGaN layer. As the InN layer is used as a p-type nitride semiconductor, the hole concentration is increased compared to the GaN layer.

According to the embodiments of the present invention, by adopting the p-type InN / InGaN (GaN) multilayer film, the crystallinity of the p-type nitride semiconductor layer formed thereon can be improved, and the hole concentration in the multilayer film can be increased. In addition, it is possible to remove the energy barrier to the hole by excluding the electron blocking layer. Accordingly, the forward voltage of the light emitting diode can be lowered, and the hole can be smoothly introduced into the active region. On the other hand, the hole concentration can be increased by using the InN layer as a p-type nitride semiconductor.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, the light emitting diode includes a substrate 21, an n-type nitride semiconductor layer 27, an active region 29 having a multi-quantum well structure, a p-type multilayer film 31, and a p-type nitride semiconductor layer 33. It includes. In addition, a nuclear layer 23 and an undoped GaN layer (u-GaN) 25 may be interposed between the substrate 21 and the n-type nitride semiconductor layer 27. In addition, the transparent electrode 35 and the p-electrode 37 may be positioned on the p-type nitride semiconductor layer 33, and the n-electrode 39 may be positioned on the n-type nitride semiconductor layer 27. .

The substrate 21 is a substrate for growing a gallium nitride-based semiconductor layer, but is not particularly limited, such as sapphire, SiC, spinel, but preferably, as shown, may be a patterned sapphire substrate (PSS).

The nuclear layer 23 may be formed of (Al, Ga) N at a low temperature of 400 ~ 600 ℃ to grow u-GaN (25) on the substrate 21, preferably formed of AlN. The nuclear layer may be formed to a thickness of about 25nm.

The u-GaN layer 25 is a layer for alleviating the occurrence of defects such as dislocations between the substrate and the n-type nitride semiconductor layer 27, and is grown at a relatively high temperature. The n-type nitride semiconductor layer 27 is a layer on which the n-electrode 39 is formed, and may be doped with n-type impurities such as Si or Ge. The n-type nitride semiconductor layer 27 may be a single layer, but is not limited thereto, and may be a multilayer.

The active region 29 has a multi-quantum well structure in which a barrier layer and a quantum well layer are alternately stacked, and the quantum well layer includes an InGaN layer. Furthermore, it is preferable that the barrier layer also includes an InGaN layer. In particular, by taking the InGaN / InGaN quantum well structure, the conductivity of the quantum well structure can be improved, and thus the forward voltage of the light emitting diode can be lowered. Barrier layers in the multi-quantum well structure may include a relatively thicker barrier layer, a wider bandgap barrier layer, or a barrier layer doped with p-type impurities.

The p-type multilayer film 31 has a structure in which an InN layer 31a and an In _x Ga _1-x N (0 ≦ x <1) layer 31b are alternately stacked two or more times. These layers 31a and 31b may be doped with p-type impurities, such as Mg, in which case it is preferable that the InN layer 31a is doped to a higher impurity concentration than the InGaN layer 31a. Accordingly, the hole concentration in the multilayer film 31 can be increased.

These multi-layer films may be formed by repeatedly supplying and blocking Ga sources, and the growth temperatures of the InN layer and the In _x Ga _1-x N layer may be different from each other. In general, InN or InGaN is grown at a relatively low temperature compared to the GaN layer. If the temperature of the substrate is raised after the InGaN layer is grown, the InGaN layer on the surface is dissociated, and the thickness decreases and the crystal quality deteriorates. Therefore, after forming the quantum well structure, the layer in contact with the active region is preferably an InN layer or an InGaN layer.

The thickness of each layer in the multilayer film 31 may be formed to a thickness of 5 ~ 200Å, it may be formed in a superlattice structure. The overall thickness of the multilayer film 31 is not particularly limited, but if excessively thick, Vf may increase, so that the overall thickness of the active region is preferably about 100 to 150 nm or less. In addition, the In _x Ga _1-x N layer 31b can be made thicker than the InN layer 31a. By forming a thin InN layer having a narrow band gap, current dispersion can be assisted.

It is preferable that the InN layer 31a or the In _x Ga _1-x N layer 31b is in contact with the active region and in contact with the InGaN barrier layer. However, as described above, when the GaN layer 31b is used, it is preferable that the InN layer 31a is in contact with the active region as compared with the GaN layer 31b. The InGaN barrier layer in contact with the multilayer film 31 preferably has a narrower bandgap than other barrier layers.

Meanwhile, the In _x Ga _1-x N layers 31b may have the same In content, but are not limited thereto and may have different In contents. For example, the In content in the In _x Ga _1-x N layers 31b may increase as the active region 29 approaches.

The p-type nitride semiconductor layer 33 may be formed of GaN. The p-type nitride semiconductor layer 33 may be a single layer, but is not limited thereto, and may be a multilayer.

In addition, a transparent electrode 35 such as Ni / Au or indium tin oxide (ITO) is formed on the p-type nitride semiconductor layer 33, and the p-electrode 37 is formed thereon, for example, by a lift-off process. Can be. In addition, an n-electrode 39 such as Ti / Al may be formed on the n-type nitride semiconductor layer 27 by a lift-off process.

While some embodiments of the present invention have been described by way of example, those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential features thereof. Therefore, the embodiments described above should not be construed as limiting the technical spirit of the present invention but merely for better understanding. The scope of the present invention is not limited by these embodiments, and should be interpreted by the following claims, and the technical spirit within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Claims (11)

an n-type nitride semiconductor layer; p-type nitride semiconductor layer; An active region interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer and including an InGaN quantum well layer; And And a p-type multilayer film interposed between the p-type nitride semiconductor layer and the active region and having an InN layer and an In _x Ga _1-x N (0 ≦ x <1) layer alternately stacked at least twice. The light emitting diode of claim 1, wherein the multilayer film includes a p-type InN layer doped with p-type impurities. The light emitting diode of claim 2, wherein a p-type impurity concentration of the p-type InN layer is higher than a p-type impurity concentration of the In _x Ga _1-x N (0 ≦ x <1) layer. The light emitting diode of claim 1, wherein the multilayer film is in contact with the active region. The light emitting diode of claim 4, wherein the active region of the quantum well structure has a stacked structure of an InGaN quantum well layer and an InGaN barrier layer. The light emitting diode of claim 5, wherein the multilayer film is in contact with an InGaN barrier layer in the active region. The light emitting diode of claim 6, wherein the InGaN barrier layer in contact with the multilayer film has a relatively narrow energy band gap compared to other barrier layers. The light emitting diode of claim 1, wherein the InN layer and the In _x Ga _1-x N (0 ≦ x <1) layer have a thickness of about 5 μs to about 200 μs. The light emitting diode of claim 1, wherein the multilayer film has a superlattice structure. The light emitting diode of claim 1, wherein the In _x Ga _1-x N (0 ≦ x <1) layers in the multilayer film contain more In as closer to the active region. an n-type nitride semiconductor layer; p-type nitride semiconductor layer; An active region interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer and including an InGaN quantum well layer; And A light emitting diode comprising an InN layer located above the active region.

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