KR101393356B1 - Light emitting diode - Google Patents

Abstract

A light emitting diode is disclosed. The light emitting diode includes a substrate, an n-type contact layer formed on the substrate, a p-type contact layer formed on the n-type contact layer, a multi quantum well structure interposed between the n-type contact layer and the p- And an undoped GaN layer interposed between the substrate and the n-type contact layer. On the other hand, the n-type contact layer is a super lattice structure in which an n-type InGaN layer and an undoped InGaN layer are alternately laminated in contact with the undoped GaN layer and the active region, respectively. In addition, the n-type InGaN layer and the undoped InGaN layer have different composition ratios. By forming the n-type contact layer with an InGaN / InGaN superlattice structure, the strain generated in the active region of the light emitting diode can be relaxed and the structure can be prevented from being complicated.

Light emitting diode, superlattice, contact layer, InGaN

Description

[0001] LIGHT EMITTING DIODE [0002]

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having a very simple structure while reducing strain generated in an active layer.

In general, nitride-based semiconductors are widely used as ultraviolet light, blue / green light emitting diodes, or laser diodes as light sources for full color displays, traffic lights, general illumination and optical communication devices. Such a 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 by recombination of electrons and holes in the quantum well layer in the active region .

Such a conventional nitride compound semiconductor has a lattice mismatch of 11% between GaN and InN. Therefore, a strong strain is generated in the quantum well and the quantum barrier interface in the InGaN-based multiple quantum well structure. Such strain induces a piezoelectric field in the quantum well, resulting in a decrease in internal quantum efficiency.

In addition, the strain generated in the multiple quantum well structure is affected by the n-type nitride semiconductor layer adjacent to the active layer. The greater the lattice mismatch between the n-type nitride semiconductor layer, e.g., the n-type contact layer and the quantum well layer, the greater strain is induced in the active region.

A technique of forming a superlattice structure in which a first nitride semiconductor layer and a second nitride semiconductor layer which are different in composition from each other are alternately stacked is used between the n-type GaN contact layer and the active layer to reduce the strain generated in the active region . However, when a superlattice structure is formed between the n-type contact layer and the active layer, the superlattice structure must be etched to form an n-electrode in addition to the growth of the n-type contact layer and the superlattice structure. There is a problem to be solved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light emitting diode capable of alleviating strain induced in an active layer.

Another object of the present invention is to provide a light emitting diode which is simple in structure and can simplify a manufacturing process.

According to an aspect of the present invention, there is provided a light emitting diode including a substrate, an n-type contact layer formed on the substrate, a p-type contact layer formed on the n-type contact layer, an active region of a multiple quantum well structure interposed between the p-type contact layers and including an InGaN layer, and an undoped GaN layer interposed between the substrate and the n-type contact layer. On the other hand, the n-type contact layer is a superlattice structure in which an n-type InGaN layer and an undoped InGaN layer are alternately laminated in contact with the undoped GaN layer and the active region, respectively. In addition, the n-type InGaN layer and the undoped InGaN layer have different composition ratios. By forming the n-type contact layer with an InGaN / InGaN superlattice structure, the strain generated in the active region of the light emitting diode can be relaxed and the structure can be prevented from being complicated.

An (Al, Ga) N core layer may be interposed between the substrate and the undoped GaN layer, and the core layer may be formed of AlN.

On the other hand, the n-type impurity doped in the n-type InGaN layer may be Si.

The n-type InGaN layer may have a smaller In content than the undoped InGaN layer. Further, the n-type InGaN layer may have a smaller In content than the InGaN layer in the active region.

Meanwhile, the undoped GaN may be formed to a thickness within a range of 4 to 4.5 mu m, and the n-type contact layer may be formed to a thickness within a range of 1 to 1.5 mu m. Conventionally, in order to reduce the dislocation density caused by the lattice mismatch between the substrate and GaN and lower the lateral resistance of the n-type contact layer, the undoped GaN has a thickness of about 2 탆 and the n-type GaN contact layer has a thickness of about 4 탆 Lt; / RTI > However, in the present invention, by adopting the contact layer of InGaN / InGaN superlattice structure, the resistance in the lateral direction can be lowered and the thickness thereof can be reduced. Further, by decreasing the thickness of the n-type contact layer, the total thickness of the undoped GaN and the n-type contact layer is made thinner than the total thickness of the conventional undoped GaN and the contact layer, can do.

The undoped GaN layer has better crystallinity than the Si-doped GaN layer. Therefore, as the thickness of the undoped GaN layer is increased, the crystallinity of the gallium nitride-based semiconductor layers formed thereon is improved.

According to the embodiments of the present invention, by forming the n-type contact layer with an InGaN / InGaN superlattice structure, the strain generated in the active region of the light emitting diode can be relaxed and its structure can be prevented from being complicated. Furthermore, the undoped GaN layer can be formed to be relatively thicker than the conventional one, and the crystallinity of the gallium nitride-based semiconductor layers formed thereon can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 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. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, etc. of constituent elements can be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

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

1, the light emitting diode includes a substrate 21, an undoped GaN layer (u-GaN) 25, an n-type contact layer 27, an active region 29 of a multiple quantum well structure, (33). A core layer 23 may be interposed between the substrate 21 and the u-GaN layer 25 and a p-type cladding layer 31 may be interposed between the active region 29 and the p- Can be intervened. In addition, the transparent electrode 35 and the p-electrode 37 may be located on the p-type contact layer 33, and the n-electrode 39 may be located on the n-type contact layer 27.

The substrate 21 is a substrate for growing a gallium nitride based semiconductor layer. The substrate 21 is not limited to sapphire, SiC, or spinel, but may be a patterned sapphire substrate (PSS), as shown in the figure.

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

The u-GaN layer 25 is grown between the substrate and the n-type contact layer 27 at a relatively high temperature as a layer for mitigating the occurrence of defects such as dislocation. The conventional u-GaN layer is usually grown to a thickness of about 2 탆, but in the present embodiment, it may be formed to have a relatively thick thickness within the range of 4 to 4.5 탆. Since the u-GaN layer is grown without impurity doping, it has a relatively good crystallinity as compared with the impurity-doped GaN layer. Therefore, it is possible to improve the quality of the light emitting diode by forming the u-GaN layer relatively thick.

The n-type contact layer 27 is located between the u-GaN layer 25 and the active region 29 and contacts them. The n-type contact layer 27 has a superlattice structure in which an n-type InGaN layer 27a doped with an n-type impurity and an undoped InGaN layer 27b are alternately laminated. The impurities to be doped into the n-type InGaN layer 27a may be various such as Si and Ge, but Si which is usually used is preferable.

On the other hand, the n-type InGaN layer and the undoped InGaN layer have different composition ratios. That is, the In composition ratio of the InGaN layers and the composition ratio of Ga are different from each other. For example, the In content of the n-type InGaN layer may be more or less than that of the undoped InGaN layer. As the In content decreases, the energy bandgap decreases, so that the electrons can gather in the layer having a large amount of In. Therefore, it is preferable that the energy band gap of the n-type InGaN layer is wider than the energy band gap of the undoped InGaN layer which is not doped with the impurity, and therefore the In content thereof is preferably smaller than that of the undoped InGaN layer.

The active region 29 has a multiple quantum well structure in which GaN quantum barrier layers and InGaN quantum well layers are alternately stacked. The In composition ratio in the InGaN quantum well layer is determined by a desired light wavelength.

On the other hand, it is preferable that the In content in the n-type InGaN layer 27a and / or the undoped InGaN layer 27b in the n-type contact layer 27 is smaller than the In content in the quantum well layer. As a result, the charge can be better confined within the active region 29, and the luminous efficiency can be improved.

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

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

(Example)

A light emitting diode having the structure shown in FIG. 1 was fabricated. That is, after the AlN core layer 23 is grown to a thickness of 25 nm on the patterned sapphire substrate 21, a u-GaN layer 25 is formed thereon to a thickness of 4.5 mu m and a total thickness of 1.5 mu m an n-type contact layer 27 of n-InGaN / u-InGaN superlattice structure, and a multi quantum well structure of 11 periods total thickness of about 110 nm were grown. Thereafter, the p-type AlGaN cladding layer 31 and the p-type GaN contact layer 33 were grown to fabricate a light emitting diode according to this example.

(Comparative Example)

The light emitting diode having a structure similar to that of the light emitting diode according to the present embodiment was removed. However, there is a difference from the light emitting diode according to the present embodiment in that a u-GaN layer is grown to a thickness of 2 탆 and an n-type contact layer is grown to 4 탆 with a single GaN.

Table 1 summarizes the characteristics of the LEDs according to the embodiments and the comparative examples.

Wavelength (@ 20mA)
(nm) Vf (@ 1uA)
(V) Vf (@ 20mA)
(V) Po (@ 20mA)
(mW) Po (@ 80mA)
(mW) Remarks Comparative Example 457.24 2.11 3.06 14.57 44.41 GaN contact layer 453.73 2.20 3.09 14.42 44.73 Example 449.15 2.23 2.92 17.18 54.75 (InGaN / InGaN)
Superlattice contact layer 448.41 2.22 2.91 17.19 54.89

As can be seen from Table 1, as the n-type contact layer 27 of the n-InGaN / u-InGaN superlattice structure was adopted, the peak wavelength of emitted light was shortened and the light output was improved. In addition, the voltage at 1uA, that is, the turn-on voltage, increases, and the forward voltage decreases. This is because the strain of the active region is relaxed and the crystallinity of the active region is improved by adopting the n-type contact layer 27 of n-InGaN / u-InGaN superlattice structure.

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

Claims (4)

Board; An n-type contact layer formed on the substrate; A p-type contact layer formed on the n-type contact layer; An active region of a multiple quantum well structure interposed between the n-type contact layer and the p-type contact layer and including an InGaN layer; And And an undoped GaN layer interposed between the substrate and the n-type contact layer, Wherein the n-type contact layer is in a super lattice structure in contact with the undoped GaN layer and the active region, wherein an n-type InGaN layer doped with an n-type impurity and an undoped InGaN layer are alternately laminated, Wherein the n-type InGaN layer and the undoped InGaN layer have different composition ratios. The light emitting diode according to claim 1, further comprising an AlN core layer interposed between the substrate and the undoped GaN layer. The light emitting diode of claim 1, wherein the n-type InGaN layer is Si-doped. The light emitting diode according to claim 1, wherein the n-type InGaN layer has a smaller In content than the InGaN layer and the undoped InGaN layer in the active region.

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