KR20110100569A - Nitride semiconductor device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor element, and an embodiment of the present invention is formed between an n-type nitride semiconductor layer, a p-type nitride semiconductor layer, and the n-type and p-type nitride semiconductor layers, and includes a quantum well layer and a quantum well layer. An active layer formed by alternately stacking barrier layers with each other, an electron blocking layer formed between the active layer and the p-type nitride semiconductor layer, and between the active layer and the electron blocking layer, wherein the energy level is based on the valence band. A nitride semiconductor device including a hole collector layer having a region higher than a doping level of a p-type nitride semiconductor layer is provided.
According to the present invention, a light emitting efficiency is improved by increasing the concentration of holes entering the active layer, and a nitride semiconductor light emitting device capable of solving the problem of deterioration of quantum efficiency during high current injection can be obtained.

Description

Nitride Semiconductor Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor device, and more particularly to a nitride semiconductor light emitting device in which light emission efficiency can be improved by increasing the concentration of holes entering the active layer.

In general, nitride semiconductors are widely used in green or blue light emitting diodes (LEDs) or laser diodes (LDs), which are provided as light sources in full-color displays, image scanners, various signal systems, and optical communication devices. Such a nitride semiconductor device can be provided as a light emitting device having an active layer emitting a variety of light, including blue and green using the recombination principle of electrons and holes.

After such a nitride light emitting device (LED) has been developed, many technological advances have been made, and the range of its use has been expanded, and thus, many studies have been conducted as general lighting and electric light sources. In particular, in the past, nitride light emitting devices have been mainly used as components applied to mobile products of low current / low power, but recently, their application ranges are gradually expanded to high current / high power fields.

1 is a cross-sectional view showing a general nitride semiconductor device. Referring to FIG. 1, a general nitride semiconductor device 10 includes a substrate 11, an n-type nitride semiconductor layer 12, an active layer 13, and a p-type nitride semiconductor layer 15, and the active layer 13 And an electron blocking layer (EBL) 14 between the p-type nitride semiconductor layer 15. The p-type electrode 16b is formed on the mesa-etched p-nitride semiconductor layer 15, and the n-type electrode 16a is formed on the exposed top surface of the n-type nitride semiconductor layer 12. The electron blocking layer 14 may improve electron recombination efficiency of the carrier in the active layer 13 by preventing electrons having higher mobility than holes from overflowing the p-type nitride semiconductor layer 15. It is adopted. However, the electron blocking layer 14 may function as a barrier not only for electrons but also for holes, and thus, the concentration of holes entering the active layer 13 beyond the electron blocking layer 14 may be lowered. .

An object of the present invention is to provide a nitride semiconductor light emitting device which can improve the luminous efficiency by increasing the concentration of holes entering the active layer.

In order to realize the above technical problem, an embodiment of the present invention,

an active layer formed between an n-type nitride semiconductor layer, a p-type nitride semiconductor layer, the n-type and p-type nitride semiconductor layers, and a quantum well layer and a quantum barrier layer alternately stacked with each other, the active layer and the p An electron blocking layer formed between the type nitride semiconductor layer and a hole collector layer formed between the active layer and the electron blocking layer and having a region having an energy level higher than a doping level of the p-type nitride semiconductor layer based on the valence band; It provides a nitride semiconductor device comprising a.

In an embodiment of the present disclosure, the doping level of the p-type nitride semiconductor layer may be an Mg doping level.

In one embodiment of the present invention, it is preferable that the difference between the energy level of the hole collector layer and the energy level of the p-type nitride semiconductor layer is greater than 170 meV based on the valence band.

In one embodiment of the present invention, it is preferable that the hole collector layer has a lower energy level based on the valence band than the quantum well layer of the active layer adjacent thereto.

In one embodiment of the present invention, the hole collector layer may be formed of In _x Ga _{1 - x} N (0 ≦ _x ≦ 1). In this case, the quantum well layer of the active layer adjacent to the hole collector layer may have a higher indium content than the hole collector layer.

In an embodiment of the present invention, the thickness of the region in which the energy level of the hole collector layer is higher than the doping level of the p-type nitride semiconductor layer based on the valence band is less than or equal to 100 μs, rather than the quantum well layer of the active layer adjacent thereto. It is preferable to be thick.

In one embodiment of the present invention, when the energy level of the hole collector layer based on the valence band is higher than the doping level of the p-type nitride semiconductor layer as the first layer, the hole collector layer is the valence band On the basis of the second layer may have a lower energy level than the first layer. In this case, the second layer may be in contact with the electron blocking layer to form an interface, and the thickness of the second layer is preferably 20 kPa or less.

According to the present invention, a light emitting efficiency is improved by increasing the concentration of holes entering the active layer, and a nitride semiconductor light emitting device capable of solving the problem of deterioration of quantum efficiency during high current injection can be obtained.

1 is a cross-sectional view showing a general nitride semiconductor device.
FIG. 2 is a cross-sectional view illustrating a nitride semiconductor device according to one embodiment of the present invention, and FIG. 3 is an enlarged view of a region indicated by A in FIG. 2. 4 schematically shows the valence band energy level in the region shown in FIG. 3.
5 schematically shows energy levels of active layers in a conventional nitride semiconductor device.
6 shows simulation results of quantum efficiencies of a nitride semiconductor device employing a hole collector layer and a conventional nitride semiconductor device.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity, and the elements denoted by the same reference numerals in the drawings are the same elements.

FIG. 2 is a cross-sectional view illustrating a nitride semiconductor device according to one embodiment of the present invention, and FIG. 3 is an enlarged view of a region indicated by A in FIG. 2. 4 schematically shows the valence band energy level in the region shown in FIG. 3.

First, referring to FIG. 2, the nitride semiconductor element 100 according to the present embodiment includes a substrate 101, an n-type nitride semiconductor layer 102, an active layer 103, an electron blocking layer 105, and a p-type nitride. The semiconductor layer 106 is formed, and a hole collector 104 layer is formed between the active layer 103 and the electron blocking layer 105. An n-type electrode 107a may be formed on an exposed surface of the n-type nitride semiconductor layer 102, and a p-type electrode 107b may be formed on an upper surface of the p-type nitride semiconductor layer 106. Although not shown, an ohmic contact layer made of a transparent electrode material or the like may be formed between the p-type nitride semiconductor layer 106 and the p-type electrode 107b. In the present embodiment, the n-type and p-type electrodes 107a and 107b are exemplified in a horizontal nitride semiconductor device structure in which the n-type and p-type electrodes are disposed to face the same direction. It will be readily understood by one skilled in the art that the sapphire substrate can be applied to the case).

The substrate 101 is for nitride single crystal growth, and in general, a sapphire substrate may be used. Sapphire substrates are hexagonal-Rhombo R3c symmetric crystals with lattice constants in the c-axis and a-axis directions of 13.001 Å and 4.758 각각, respectively, C (0001) plane, A (1120) plane, and R ( 1102) surface and the like. In this case, the C plane is mainly used as a nitride growth substrate because the C surface is relatively easy to grow and stable at high temperatures. Of course, therefore the decision of SiC, GaN, ZnO, MgAl ₂ O _4, MgO, LiAlO ₂ and LiGaO ₂ substrate or the like is also a nitride semiconductor single crystal use is possible and, furthermore, is grown on the substrate 101 made of the type It is also possible to grow a buffer layer for quality improvement, for example, an undoped GaN layer.

The n-type and p-type nitride semiconductor layers 102 and 106 are Al _x In _y Ga _(1-xy) N composition formulas, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1. N-type impurity and p-type impurity can be made of a semiconductor material doped, typically, GaN, AlGaN, InGaN. In addition, Si, Ge, Se, Te and the like may be used as the n-type impurity, and the p-type impurity is Mg, Zn, Be and the like. The n-type and p-type nitride semiconductor layers 102 and 106 may be grown by MOCVD or HVPE processes known in the art.

The active layer 103 formed between the n-type and p-type nitride semiconductor layers 102 and 106 emits light having a predetermined energy by recombination of electrons and holes, and the band gap energy is adjusted according to the indium content. _x Ga _{1 - x} N (0 ≦ _x ≦ 1). In this case, as shown in FIG. 3, the active layer 103 may have a multi-quantum well (MQW) structure in which a quantum barrier layer 103a and a quantum well layer 103b are alternately stacked.

The electron blocking layer 105 may block electrons having a higher mobility than the holes from overflowing the active layer 103. To this end, the band gap energy may be higher than that of the active layer 103, and specifically, may be made of a material such as Al _x Ga _{1 - x} N (0 ≦ _x ≦ 1). In this case, the band gap energy of the electron blocking layer 105 may be appropriately adjusted by the aluminum content. However, as described above, the electron blocking layer 105 increases the recombination probability in the active layer 103 by blocking the overflow of electrons, but may also function to block the injection of holes.

In this embodiment, in order to reduce the hole blocking function of the electron blocking layer 105, the hole collector layer 104 is employed between the active layer 103 and the electron blocking layer 105, the hole collector layer 104 provides an appropriate energy level condition to increase the probability that holes injected from the p-type nitride semiconductor layer 106 can be injected into the active layer 103 by tunneling or crossing the electron blocking layer 105. Referring to FIG. 4, the hole collector 104 may be divided into a first layer 104a and a second layer 104b, and the first layer 104a may be formed of both the active layers 103. An interface is formed with the well layer 103b, and the second layer 104b forms an interface with the electron blocking layer 105. In the present embodiment, the structure of the hole collector layer 104 is divided into two layers. However, in some cases, the hole collector 104 may be formed using only the first layer 104a.

The first layer 104a of the hole collector layer 104 has a lower energy level Ev than the quantum well layer 103b and a higher energy level Ev than the quantum barrier layer 103a. In this case, the energy level Ev described in the present embodiment is based on a valence band. Furthermore, the energy level of the first layer 104a is higher than the doping level of the p-type nitride semiconductor layer 106, and the concentration of holes for tunneling the electron blocking layer 105 increases due to such energy level conditions. Can be. 4 illustrates a case where Mg is used as the p-type impurity, assuming that the p-type nitride semiconductor layer 105 and the quantum barrier layer 103a are made of the same material, for example, GaN. The energy level difference, ΔEv, of layer 104a must be greater than the energy level value raised by Mg doping. In view of this, it is preferable that ΔEv is greater than about 170 meV.

In this case, the first layer 104a is formed of In _x Ga _{1 - x} N (0 ≦ _x ≦ 1), and the energy level may be appropriately adjusted by adjusting the indium content. In order to have an energy level as shown in FIG. 4, the indium content of the first layer 104a may be lower than that of the quantum well layer 103b and higher than that of the quantum barrier layer 103a. In addition, the thickness t1 of the first layer 103a is thicker than that of the quantum well layer 103b, but preferably not more than about 100 GPa.

On the other hand, the second layer 104b formed between the first layer 104a and the electron blocking layer 105 has an energy level between the first layer 104a and the electron blocking layer 105. For example, the quantum barrier layer 105 may have the same energy level as that of the quantum barrier layer 105. The second layer 104b may function as a capping layer protecting the first layer 104a, which may be made of InGaN, and furthermore, the first layer (not shown) in the electron blocking layer 105 grown thereon. 104a) serves to prevent the diffusion of Mg and the like. In consideration of these matters, the thickness t of the second layer 104b is preferably 20 kPa or less.

As a result of comparing the quantum efficiency of the nitride semiconductor device employing the hole collector layer with the conventional structure, FIG. 6 shows the quantum efficiency of the nitride semiconductor device employing the hole collector layer and the conventional nitride semiconductor device. The simulation results are shown. In this case, the active layer structure of the conventional nitride semiconductor element is a quantum barrier layer having the same thickness instead of the hole collector layer as shown in FIG. Referring to FIG. 6, in the case of a conventional nitride semiconductor device (dotted line), the quantum efficiency in the low current region is relatively excellent, but when a high current is applied, the quantum efficiency tends to be significantly decreased, that is, efficiency droop occurs. . In comparison, an efficiency droop problem does not occur in a nitride semiconductor element (solid line) employing a hole collector layer, and thus, it is suitable for use in lighting devices and the like requiring operation at high current.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is defined by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims, and the appended claims. Will belong to the technical spirit described in.

101: substrate 102: n-type nitride semiconductor layer
103: active layer 104: hole collector layer
105: electron blocking layer 106: p-type nitride semiconductor layer
107a and 107b: n-type and p-type electrodes 103a: quantum barrier layer
103b: quantum well layer 104a, 104b: first and second layers

Claims (10)

an n-type nitride semiconductor layer;
p-type nitride semiconductor layer;
An active layer formed between the n-type and p-type nitride semiconductor layers, wherein an quantum well layer and a quantum barrier layer are alternately stacked;
An electron blocking layer formed between the active layer and the p-type nitride semiconductor layer; And
A hole collector layer formed between the active layer and the electron blocking layer and having a region having an energy level higher than a doping level of the p-type nitride semiconductor layer based on a valence band;
A nitride semiconductor device comprising a.
The method of claim 1,
The doping level of the p-type nitride semiconductor layer is a nitride semiconductor device, characterized in that the doping level.
The method of claim 1,
The difference between the energy level of the hole collector layer and the energy level of the p-type nitride semiconductor layer on the basis of the valence band is greater than 170meV.
The method of claim 1,
The hole collector layer has a lower energy level based on the valence band than the quantum well layer of the active layer adjacent thereto.
The method of claim 1,
The hole collector layer is formed of In _x Ga _{1 - x} N (0≤x≤1).
The method of claim 5,
The quantum well layer of the active layer adjacent to the hole collector layer has a higher indium content than the hole collector layer.
The method of claim 1,
A nitride semiconductor device having an energy level based on a valence band in the hole collector layer having a thickness higher than a doping level of the p-type nitride semiconductor layer is 100 Å or less, and is thicker than a quantum well layer of the active layer adjacent thereto. .
The method of claim 1,
When the energy level of the hole collector layer based on the valence band is higher than the doping level of the p-type nitride semiconductor layer as the first layer, the hole collector layer is formed on the valence band than the first layer. A nitride semiconductor device comprising a second layer having a low energy level.
The method of claim 8,
And the second layer is in contact with the electron blocking layer to form an interface.
The method of claim 8,
The thickness of the said 2nd layer is a nitride semiconductor element characterized by the above-mentioned.

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