KR20100022593A - Light emitting diode - Google Patents

Abstract

PURPOSE: A light emitting diode is provided to relieve an active region by forming an n-type contact layer with InGaN superlattice structure. CONSTITUTION: A light emitting diode comprises a substrate(21), n-type contact layer(27), p-type contact layer(33), an active layer of a multiple quantum well, and undoped GaN layer(25). The n-type contact layer is formed on the substrate. The p-type contact layer is formed on the n-type contact layer. The active region is interposed between the n-type contact layer and p-type contact layer. The active region comprises an InGaN layer. The undoped GaN layer is interposed between the substrate and the n-type contact layer. The n-type contact layer has a superlattice structure. The n-type contact layer is formed by laminating the n-type InGaN layer and the undoped InGaN layer. The n-type InGaN layer and the undoped InGaN layer have the different composition ratio.

Description

Light Emitting Diodes {LIGHT EMITTING DIODE}

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having a very simple structure while reducing the strain generated in the active 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 addition, 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 mismatch of the lattice constant between the n-type nitride semiconductor layer, such as the n-type contact layer and the quantum well layer, the greater the strain in the active region.

In order to reduce the strain generated in the active region, a technique of forming a superlattice structure in which a first nitride semiconductor layer and a second nitride semiconductor layer having different compositions are alternately stacked between the n-type GaN contact layer and the active layer is used. . However, when the superlattice structure is formed between the n-type contact layer and the active layer, the superlattice structure must be etched to form the n-electrode in addition to the growth of the n-type contact layer and the superlattice structure, which makes the light emitting diode manufacturing process complicated. There is a problem.

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 layer.

Another problem to be solved by the present invention is to provide a light emitting diode that can simplify the manufacturing process because the structure is simple.

In order to solve the above problems, a light emitting diode according to embodiments of the present invention is a substrate, an n-type contact layer formed on the substrate, a p-type contact layer formed on the n-type contact layer, the n-type contact layer and the An active region of a multi-quantum well structure interposed between the p-type contact layer and the InGaN layer, and an undoped GaN layer interposed between the substrate and the n-type contact layer. The n-type contact layer is a superlattice structure in which the n-type InGaN layer and the undoped InGaN layer which are in contact with the undoped GaN layer and the active region are alternately stacked. In addition, the n-type InGaN layer and the undoped InGaN layer have different composition ratios. By making the n-type contact layer have an InGaN / InGaN superlattice structure, strain generated in the active region of the light emitting diode can be alleviated, and the structure can be prevented from being complicated.

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

Meanwhile, 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. In addition, the n-type InGaN layer may have a smaller In content than the InGaN layer in the active region.

On the other hand, the undoped GaN may be formed to a thickness within the range of 4 ~ 4.5㎛, the n-type contact layer may be formed to a thickness within the range of 1 ~ 1.5㎛. Conventionally, in order to reduce the dislocation density caused by the lattice mismatch between the substrate and GaN and to lower the lateral resistance of the n-type contact layer, the undoped GaN is approximately 2 μm thick and the n-type GaN contact layer is about 4 μm. It formed in the thickness of. However, in the present invention, by adopting an InGaN / InGaN superlattice contact layer, the resistance in the lateral direction can be lowered and the thickness thereof can be reduced. In addition, as the thickness of the n-type contact layer is reduced, 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, but relatively thicker undoped GaN layer is formed. 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 embodiments of the present invention, the n-type contact layer has an InGaN / InGaN superlattice structure, which can reduce strain generated in the active region of the light emitting diode and prevent the structure from being complicated. Furthermore, the undoped GaN layer can be formed relatively thicker than in the related art, thereby improving the crystallinity of the gallium nitride based semiconductor layers formed thereon.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; The following embodiments are provided as examples to ensure that the spirit of the present invention to those skilled in the art will fully convey. 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 undoped GaN layer (u-GaN, 25), an n-type contact layer 27, an active region 29 having a multi-quantum well structure, and a p-type contact layer. (33). In addition, a nuclear 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-type contact layer 33. May be interposed. In addition, the transparent electrode 35 and the p-electrode 37 may be positioned on the p-type contact layer 33, and the n-electrode 39 may be positioned on the n-type contact 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 defects such as dislocations between the substrate and the n-type contact layer 27, and is grown at a relatively high temperature. Conventional u-GaN layer is usually grown to a thickness of about 2㎛, in this embodiment may be formed relatively thick with a thickness within the range of 4 ~ 4.5㎛. Since the u-GaN layer is grown without impurity doping, the u-GaN layer has relatively good crystallinity as compared to the GaN layer doped with impurities. Therefore, forming a relatively thick u-GaN layer can improve the quality of the light emitting diode.

The n-type contact layer 27 is positioned between the u-GaN layer 25 and the active region 29 to be in contact with each other. The n-type contact layer 27 has a superlattice structure in which an n-type InGaN layer 27a doped with n-type impurities and an undoped InGaN layer 27b are alternately stacked. Impurities doped in the n-type InGaN layer 27a may vary with Si and Ge, but Si, which is commonly used, is preferable.

On the other hand, the n-type InGaN layer and the undoped InGaN layer are different in composition ratio. In other words, the In composition ratio in these InGaN layers and hence the composition ratio of Ga are different. 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 increases, the energy band gap decreases, and thus electrons may be collected in a large In content layer. Therefore, it is preferable that the energy bandgap of the n-type InGaN layer is wider than the energy bandgap of the undoped InGaN layer which is not doped with impurities, and therefore, the In content therein is less than that of the undoped InGaN layer.

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

Meanwhile, the In content in the n-type InGaN layer 27a and / or the undoped InGaN layer 27b in the n-type contact layer 27 may be less than the In content in the quantum well layer. Accordingly, charges can be better confined within the active region 29 to improve the luminous efficiency.

Meanwhile, the p-type cladding layer 31 may be formed of conventional AlGaN, and the p-type cladding 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 contact 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 contact layer 27 by a lift off process.

(Example)

A light emitting diode having the structure as shown in FIG. 1 was manufactured. That is, after growing 25 nm of the AlN nucleus layer 23 on the patterned sapphire substrate 21, the u-GaN layer 25 is 4.5 μm on the patterned sapphire substrate 21, and the total thickness is 1.5 μm on the u-GaN layer 25. An n-type contact layer 27 having an n-InGaN / u-InGaN superlattice structure and a multi-quantum well structure having a total thickness of about 110 nm in 11 cycles were grown. Thereafter, the p-type AlGaN cladding layer 31 and the p-type GaN contact layer 33 were grown to produce a light emitting diode according to this embodiment.

(Comparative Example)

The light emitting diode having a structure similar to the light emitting diode according to the present embodiment was removed. However, it is different from the light emitting diode according to the present embodiment that the u-GaN layer is grown to a thickness of 2 μm and the n-type contact layer is grown to be 4 μm by a single GaN.

Table 1 summarizes the characteristics of the LED according to the above Examples and Comparative Examples.

Wavelength (@ 20 mA) (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, by adopting the n-type contact layer 27 of the n-InGaN / u-InGaN superlattice structure, the peak wavelength of the emitted light is shortened, the light output is improved. In addition, the voltage at 1 uA, that is, the turn-on voltage, increased and the forward voltage decreased. 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 the 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 interposed between the n-type contact layer and the p-type contact layer, the active region having a multi-quantum well structure including an InGaN layer; And Including an undoped GaN layer interposed between the substrate and the n-type contact layer, The n-type contact layer has a superlattice structure in which the n-type InGaN layer and the undoped InGaN layer which are in contact with the undoped GaN layer and the active region are alternately stacked, Wherein the n-type InGaN layer and the undoped InGaN layer have different composition ratios. The light emitting diode of claim 1, further comprising an AlN nuclear layer interposed between the substrate and the undoped GaN layer. The light emitting diode of claim 1, wherein the n-type InGaN layer is doped with Si. The light emitting diode of claim 1, wherein the n-type InGaN layer has less In content than the InGaN layer and the undoped InGaN layer in the active region.

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