KR20100056601A - Light emitting diode having superlattice layer - Google Patents

Abstract

PURPOSE: A light emitting diode with a superlattice layer is provided to alleviate a strain inside an active area by forming an InN or InxGa1-xN superlattice layer between a nitride semiconductor layer and the active area. CONSTITUTION: An active area(29) of multiple quantum wells is interposed between an n-type nitride semiconductor layer(27) and a p-type nitride semiconductor layer(33). The active area of multiple quantum wells comprises an InGaN quantum-well layer. A superlattice layer(28) is interposed between the n-type nitride semiconductor layer and an active area. The superlattice layer has a structure in which an InN layer and an InxGa1-xN(0<=x<1) layer are alternatively stacked. The In content of the InxGa1-xN(0<=x<1) layer inside the superlattice layer is less than that of an InGaN quantum-well layer inside the active area. The InxGa1-xN(0<=x<1) layer is contacted with the active area in the superlattice layer.

Description

LIGHT EMITTING DIODE HAVING SUPERLATTICE LAYER}

The present invention relates to a light emitting diode, and more particularly to a light emitting diode having a superlattice layer.

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 the conventional nitride compound semiconductor, since 11% lattice mismatch exists between GaN and InN, strong strain is generated at the interface between the quantum well and the quantum barrier in the InGaN-based multi-quantum well structure. This strain causes a piezoelectric field in the quantum well, leading to a decrease in internal quantum efficiency. In particular, in the case of the green light emitting diode, since the amount of In contained in the quantum well increases, the internal quantum efficiency is further reduced by the piezoelectric field.

On the other hand, the strain generated in the multi-quantum well structure is affected by the n-type nitride semiconductor layer adjacent to the active layer. The larger the lattice constant mismatch between the n-type nitride semiconductor layer, such as the n-type contact layer and the quantum well layer, causes a larger strain in the active region. Such strain decreases luminous efficiency by increasing lattice defects such as dislocations in the quantum well layer, and further increases the piezoelectric field in the quantum well structure to change the emission wavelength and increase the forward voltage.

The problem to be solved by the present invention is to provide a light emitting diode that can mitigate the strain caused in the active region.

Another problem to be solved by the present invention is to provide a superlattice layer that is in contact with the InGaN-based quantum well structure, and can reduce the strain caused by the InGaN-based quantum well structure.

In order to solve the above problems, the light emitting diode according to the embodiments of the present invention is interposed between the n-type nitride semiconductor layer, p-type nitride semiconductor layer, the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, InGaN quantum An active region of a multi-quantum well structure including a well layer and a superlattice layer interposed between the n-type nitride semiconductor layer and the active region. The superlattice layer has a structure in which an InN layer and an In _x Ga _1-x N (0 ≦ x <1) layer are alternately stacked. By forming an InN / In _x Ga _1-x N superlattice layer similar to the composition of the quantum well layer between the n-type nitride semiconductor layer and the active region, strain generated in the active region can be alleviated, and the crystallinity of the quantum well By improving the recombination rate of the carrier can be increased.

In particular, since the present invention uses an InN layer having a larger lattice constant than the InGaN quantum well layer, the compressive strain caused by the conventional InGaN quantum well layer can be alleviated, thereby improving luminous efficiency.

The multi-quantum well structure is preferably a structure in which the InGaN quantum well layer and the InGaN quantum barrier layer are alternately stacked. By combining the multi-quantum well structure and the InN / In _x Ga _1-x N superlattice layer, the strain in the multi-quantum well structure can be further reduced.

Preferably, the In _x Ga _1-x N layer in the superlattice layer is in contact with the active region. The In _x Ga _1-x N layer is preferably in contact with the quantum barrier layer of the multi-quantum well structure. In this case, the In _x Ga _1-x N layer and the quantum barrier layer in contact with the same preferably have the same composition, for example, the same In content.

Meanwhile, the In content of the In _x Ga _1-x N layer in the superlattice layer is preferably smaller than that of the InGaN quantum well layer in the active region. Accordingly, charges can be confined in the active region, thereby improving the recombination rate of electrons and holes.

In addition, the In _x Ga _1-x N layer in the superlattice layer may be doped with a higher impurity concentration than the InN layer. Furthermore, the InN layer may be intentionally not doped with impurities. Accordingly, electrons can be smoothly injected from the superlattice layer into the active region, and can also assist current dispersion.

Meanwhile, the In content of the In _x Ga _1-x N layers in the superlattice layer may be the same, but is not limited thereto. That is, the In content of the In _x Ga _1-x N layers in the superlattice layer may be different. Preferably, the In _x Ga _1-x N layers in the superlattice layer may have more In content as the closer to the active region.

According to another aspect of the present invention, a light emitting diode includes an InN layer, an In _x Ga _1-x N (0 <x <1) layer, and a GaN interposed between the n-type nitride semiconductor layer and the active region. The layers may have a structure in which alternating layers are stacked. By alternately stacking these layers, the same effect as the superlattice layer in which the InN layer and the In _x Ga _1-x N layer are alternately stacked can be achieved.

Meanwhile, the active region may be a multi-quantum well structure in which an InGaN quantum well layer and an InGaN quantum barrier layer are alternately stacked, wherein an InGaN (0 <x <1) layer in the superlattice layer is in contact with the active region. desirable.

InGaN (0 <x <1) and GaN layers may be doped with impurities, and the InN layer may not be intentionally doped in the superlattice layer, and InGaN (0 <x <1) may be intentionally not doped in the superlattice layer. ) And GaN layers may be doped with impurities at a higher concentration than the InN layers.

According to embodiments of the present invention, an InGaN layer is formed by forming an InN / In _x Ga _1-x N superlattice layer, or an InN / In _x Ga _1-x N / GaN superlattice layer between a nitride semiconductor layer and an active region. The strain generated in the active region including can be alleviated, and the recombination rate of the carrier can be increased by improving the crystallinity of the quantum well. In particular, by using the InN layer having a larger lattice constant than the InGaN quantum well layer, the compressive strain caused to the InGaN quantum well layer can be further reduced. As a result, it is possible to provide a light emitting diode with improved luminous efficiency.

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, a superlattice layer 28, an active region 29 having a multi-quantum well structure, and a p-type nitride semiconductor layer 33. It includes. In addition, the nuclear layer 23 and the undoped GaN layer (u-GaN, 25) may be interposed between the substrate 21 and the n-type nitride semiconductor layer 27, the active region 29 and the p-type nitride semiconductor The p-type cladding layer 31 may be interposed between the layers 33. 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 superlattice layer 28 has a structure in which InN layers 28a and In _x Ga _1-x N (0 ≦ x <1) layers 28b are alternately stacked. These layers 28a and 28b may be doped with n-type impurities, and in this case, it is preferable that the InGaN layer 28b is doped to a higher impurity concentration than the InN layer 28a. Also, the InN layer 28a may not be intentionally doped with impurities. These superlattice layers may be formed by repeatedly supplying and blocking Ga sources, and may have different growth temperatures of the InN layer and the In _x Ga _1-x N layer.

Impurities that are doped in the InN / InGaN superlattice layer 28, such as Si, prevent the transfer of the potential induced in the underlying layer to the upper layer. Accordingly, the crystallinity of the active region 29 formed on the superlattice layer 28 can be improved. The superlattice layer 28 may be stacked in two or more cycles, and may be preferably formed in about 20 cycles. More cycles may improve crystallinity, but are not preferred because of increased process time.

On the other hand, the thickness of each layer in the superlattice layer 28 is formed to a thickness of less than 10nm, the overall thickness of the superlattice layer 28 is not particularly limited, but if excessively thick Vf may increase, the active region It is preferable to set it as the total thickness of about 100-150 nm or less. In addition, the In _x Ga _1-x N layer 28b can be made thicker than the InN layer. By thickening the In _x Ga _1-x N layer 28b doped with impurities, the resistance may be increased to assist current dispersion.

Since the bandgap of the InGaN layer is wider than that of the InN layer, it is preferable that the In _x Ga _1-x N layer 28b is in contact with the active region 29. Further, the In composition ratio of the In _x Ga _1-x N layer 28b in the superlattice layer 28 is preferably less than the In composition ratio in the InGaN quantum well layer. In this case, the charge can be confined in the active region to emit light. The efficiency can be improved.

Meanwhile, the In _x Ga _1-x N layers 28b may all 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 28b may increase as the active region 29 approaches.

The active region 29 has a multi-quantum well structure in which a quantum 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 quantum barrier layer also includes an InGaN layer. By forming a multi-quantum well structure in which an InGaN quantum barrier layer and an InGaN quantum well layer are alternately stacked on the InN / In _x Ga _1-x N superlattice layer 28, the strain induced in the active region can be further reduced. . 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.

In the InGaN quantum barrier layer, the In content of the In _x Ga _1-x N layer in the superlattice layer 28 is preferably the same as or similar to the In content of the InGaN barrier layer. For example, when the In content of the InGaN quantum barrier layer is 2%, the In content of the InGaN layer in the superlattice layer may be about 2%. In this case, since the lattice constant difference between the InGaN quantum barrier layer and the InGaN layer in the superlattice layer is not large, it is preferable that they are in contact with each other.

Meanwhile, the p-type cladding layer 31 may be formed of conventional AlGaN, and the p-type nitride semiconductor layer 33 may be formed of GaN.

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.

Conventionally, when an InGaN-based quantum well layer is formed on a GaN layer, since the InGaN layer has a larger lattice constant than the GaN layer, compression strain is caused in the InGaN quantum well layer. As a result, a piezoelectric field is induced in the InGaN quantum well layer, thereby reducing the luminous efficiency. In contrast, according to the embodiment of the present invention, the InN layer having a larger lattice constant than the InGaN layer is adopted in the superlattice layer, and thus, the compressive strain induced in the InGaN quantum well layer can be alleviated. Furthermore, an InN layer having a larger lattice constant than an InGaN quantum well layer and an In _x Ga _1-x N layer having a smaller lattice constant than an InGaN quantum well layer are alternately stacked to form a superlattice layer, thereby causing an InGaN quantum well layer. The strain can be adjusted.

On the other hand, in the embodiment of the present invention, InN / In _x Ga _1-x N (0≤x <1) superlattice layer was described, but InN / In _x Ga _1-x N (0 <x <1) / GaN superlattice layer can be adopted. Like the InN / In _x Ga _1-x N superlattice layer, the strain induced in the InGaN quantum well layer can be controlled. In this case, the layer in contact with the quantum barrier layer may be an In _x Ga _1-x N layer or a GaN layer. When the quantum barrier layer is an InGaN layer, the In _x Ga _1-x N layer is preferably in contact with the quantum barrier layer.

In addition, the InGaN (0 <x <1) layer and the GaN layer are doped with impurities in the superlattice layer, and the InN layer is not intentionally doped, or the InGaN (0 <x <1) layer in the superlattice layer. And the GaN layer may be doped with impurities at a higher concentration than the InN layer.

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 (14)

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 superlattice layer interposed between the n-type nitride semiconductor layer and the active region and having a structure in which an InN layer and an In _x Ga _1-x N (0≤x <1) layer are alternately stacked. The light emitting diode of claim 1, wherein an In content of the In _x Ga _1-x N (0 ≦ x <1) layer in the superlattice layer is smaller than that of the InGaN quantum well layer in the active region. The light emitting diode of claim 1, wherein an In _x Ga _1-x N (0 ≦ x <1) layer is in contact with the active region in the superlattice layer. The light emitting diode of claim 1, wherein the active region of the quantum well structure has a stacked structure of an InGaN quantum well layer and an InGaN quantum barrier layer. The light emitting diode of claim 4, wherein an In _x Ga _1-x N (0 ≦ x <1) layer is in contact with an InGaN quantum barrier layer in the active region of the superlattice layer. The light emitting diode of claim 5, wherein the In _x Ga _1-x N (0 ≦ x <1) layer and the InGaN quantum barrier layer in the superlattice layer in contact with each other have the same In content. The light emitting diode of claim 1, wherein the In _x Ga _1-x N (0 ≦ x <1) layers in the superlattice layer have a higher In content as they are closer to the active region. The light emitting diode of claim 1, wherein the In _x Ga _1-x N (0 ≦ x <1) layer in the superlattice layer is doped with impurities at a higher concentration than the InN layer. The light emitting diode of claim 1, wherein the In _x Ga _1-x N (0 ≦ x <1) layer in the superlattice layer is doped with an impurity, and the InN layer is not intentionally doped. The light emitting diode of claim 9, wherein an In _x Ga _1-x N (0 ≦ x <1) layer is thicker than an InN layer in the superlattice layer. 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 superlattice layer interposed between the n-type nitride semiconductor layer and the active region and having a structure in which an InN layer, an InGaN (0 <x <1) layer, and a GaN layer are alternately stacked. The light emitting diode of claim 11, wherein an InGaN (0 <x <1) layer in the superlattice layer is in contact with the active region. The light emitting diode of claim 11, wherein an InGaN (0 <x <1) layer and a GaN layer are doped with impurities in the superlattice layer, and the InN layer is not intentionally doped. The light emitting diode of claim 11, wherein the InGaN (0 <x <1) layer and the GaN layer are doped with impurities at a higher concentration than the InN layer in the superlattice layer.

Images