KR20120022280A - Nitride semiconductor light emitting device - Google Patents

Abstract

PURPOSE: A nitride semiconductor light emitting diode is provided to efficiently prevent the bending of a multi-quantum well due to strain by delta-doping or modulation-doping an n-type impurity on a quantum barrier layer which is contiguous to a p-type nitride layer. CONSTITUTION: An n-type nitride semiconductor layer(23), an active layer(25), and a p-type nitride semiconductor layer(27) are successively formed on a substrate(21). The active layer has a multiple quantum well which is composed of a plurality of quantum barrier layers(25a) and a plurality of quantum-well layers(25b). An N-side electrode is formed in an upper side area of an n-type nitride semiconductor layer which is exposed. A transparent electrode layer(28) is formed on a p-type nitride semiconductor layer. A p-side electrode(29b) is formed on the transparent electrode layer.

Description

Nitride Semiconductor Light Emitting Device {NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE}

The present invention relates to a nitride semiconductor light emitting device, and more particularly to a nitride semiconductor light emitting device having an improved internal quantum efficiency.

Recently, a nitride semiconductor light emitting device is a light emitting device capable of generating light having a wide wavelength band including short wavelength light such as blue or green, and is gradually being escaped from the market for a simple display or a portable liquid crystal display. It is attracting much attention in the related technical field for the purpose of lighting and lighting.

As described above, as the uses of nitride semiconductor light emitting devices are diversified, the applied current is also diversified. In the case of mobile phones, it operates at a low applied current of about 20mA, but as its use expands to high-power light emitting devices for BLU and general lighting, the applied current also varies from 100mA to 350mA or more.

As the applied current of the nitride light emitting device increases, the current density of the light emitting device also increases. In the case of InGaN / GaN based nitride semiconductor light emitting devices, the external quantum efficiency decreases rapidly as the applied current density increases. This happens. This is called "efficiency droop".

In order to improve the "efficiency deterioration phenomenon" in order to enhance the confinement effect of the carrier and the luminous coupling efficiency, a wide active layer of 10 nm or more is employed in the existing light emitting device, or In is added to the barrier layer in the active layer of the multi-quantum well structure. In order to increase the external quantum efficiency at high current density. That is, by increasing the confinement effect of the carrier to keep the electrons and holes in the quantum well layer of the ultra-thin film (about 2.5 ~ 3nm) it is possible to increase the luminous coupling efficiency.

However, in the conventional light emitting device structure, due to the low hole concentration in the p-type nitride layer region and the low mobility compared to the former, even if a plurality of quantum wells are employed, only the quantum well near the p-type nitride layer actually emits light. do. This increases the concentration of the carrier in the quantum well where the actual light emission occurs, thereby increasing the probability of Auger non-emitting coupling.

In general, as the applied current increases, the concentration of carriers flowing through the light emitting device increases. At this time, since electrons have a higher mobility than holes, they do not bond with holes in the quantum well, and thus, the p-nitride layer region. An electronic overflow phenomenon will also occur.

However, when the quantum well layer and the quantum barrier layer are alternately stacked, the film quality of the finally grown quantum well layer is easily degraded, and thus the recombination probability may be reduced. Therefore, as a way to improve this, a method of improving the film quality of the last quantum well layer by increasing the thickness of the quantum barrier layer before the last quantum well layer has been proposed.

However, in this case, the bending of the quantum well layer due to the piezoelectric field becomes severe, and holes do not move to the next quantum well layer, and thus there is a problem that the internal quantum efficiency is still lowered. This phenomenon becomes more severe at high currents.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide a nitride semiconductor light emitting device which can effectively prevent the diffusion of p-type impurities into the quantum well layer while improving the film quality of the quantum barrier layer. It is.

In order to realize the above technical problem, the present invention provides a p-type and n-type nitride semiconductor layer, a plurality of quantum barrier layer and a plurality of quantum well layer is located between the p-type and n-type nitride semiconductor layer A nitride semiconductor light emitting device including an active layer stacked alternately and having a region doped with n-type impurities in a p-side quantum barrier layer that is closest to the p-type nitride semiconductor layer among the plurality of quantum barrier layers is provided.

Preferably, the other quantum barrier layer except for the p-side quantum barrier layer having the region doped with the n-type impurity may not have a region deliberately doped with the n-type impurity.

In an example, the region doped with the n-type impurity of the quantum barrier layer may be at least one n-type delta doping layer. In this case, the n-type delta doping layer may be located inside the p-side quantum barrier layer so that the quantum barrier layer region is disposed above and below the n-type delta doping layer. Further, the p-side quantum barrier layer is about 5 nm? It has a thickness of about 30nm, the n-type delta doped film is about 10? It may have a thickness of about 40 mm 3.

In another example, the region doped with the n-type impurity of the quantum barrier layer may be an n-type modulation doping region.

The n-type impurity may be at least one selected from the group consisting of Si, Ge, Sn, and Pb. The region doped with the n-type impurity may range from 5 × 10 ^{17 to} 1 × 10 ²⁰ / cm 3.

According to the present invention, the quantum barrier layer adjacent to the p-type nitride layer is delta-doped or modulated-doped n-type impurity to improve the film quality to effectively prevent bending of the multi-quantum well due to strain, furthermore, By preventing undesired diffusion, the recombination efficiency in the quantum well layer can be guaranteed.

As a result, carrier injection efficiency is improved and recombination efficiency is improved in the quantum well layer, thereby improving luminous efficiency. In particular, it is possible to alleviate the efficiency droop phenomenon that the recombination efficiency is drastically reduced according to the current density.

1 is a side cross-sectional view of a nitride semiconductor light emitting device according to one embodiment of the present invention.
FIG. 2 is an energy band diagram of an active layer of the nitride semiconductor light emitting device shown in FIG.
3 is a side cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention.
FIG. 4 is an energy band diagram of an active layer of the nitride semiconductor light emitting device shown in FIG.
FIG. 5 is a graph showing impurity concentrations for the A0-A1-A2-A3 regions shown in FIG. 3.
6 is a graph showing a change in the internal quantum efficiency according to the current density for each of the nitride semiconductor light emitting device according to the embodiment and the comparative example of the present invention.

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

1 is a side cross-sectional view showing a nitride semiconductor element 20 according to an embodiment of the present invention.

As shown in FIG. 1, the nitride semiconductor element 20 includes an n-type nitride semiconductor layer 23, an active layer 25, and a p-type nitride semiconductor layer 27 sequentially formed on the substrate 21.

The n-side electrode 29a is formed in the upper region of the n-type nitride semiconductor layer 27 exposed by mesa etching, and the transparent electrode layer 28 and the p-side electrode 29b are formed on the upper surface of the p-type nitride semiconductor layer 23. It is formed in turn.

In the present embodiment, the active layer 25 has a multi-quantum well structure composed of a plurality of quantum barrier layers 25a and a plurality of quantum well layers 25b. Among the plurality of quantum barrier layers 25a, the quantum barrier layer 25a 'adjacent to the p-type nitride semiconductor layer has a region doped with n-type impurities. The n-type impurity may be at least one selected from the group consisting of Si, Ge, Sn, and Pb. The region doped with the n-type impurity may range from 5 × 10 ^{17 to} 1 × 10 ²⁰ / cm 3.

As in the present embodiment, preferably, the other quantum barrier layer 25a except for the p-side quantum barrier layer 25'a having the region doped with the n-type impurity has a region deliberately doped with the n-type impurity. You may not.

The impurity doping method employed in this embodiment may be delta doping. That is, the region doped with the n-type impurity of the p-side quantum barrier layer 25a ′ may be an n-type delta doping film D.

As shown in FIG. 1, the n-type delta doped layer D is formed inside the p-side quantum barrier layer 25a ′ such that the quantum barrier layer region exists above and below the n-type delta doped layer D. As shown in FIG. It can be located at Although not limited to this, the p-side quantum barrier layer 25a 'is about 5 nm? It has a thickness of about 30nm, the n-type delta doped film (D) is about 10? It may have a thickness of about 40 mm 3.

2 is a schematic energy band diagram showing the structure of an improved active layer in accordance with an embodiment of the invention. It can be understood as the active layer of Fig. 1 and its surroundings.

Here, the vertical axis refers to the absolute size (eV) of the energy band gap, and the horizontal axis refers to the distance in the vertical direction from the n-type nitride semiconductor layer to the p-type nitride semiconductor layer.

Referring to FIG. 2, four quantum well layers 25b and five quantums having a larger bandgap than the quantum well layer 25b are interposed between the n-type nitride semiconductor layer 23 and the p-type nitride semiconductor layer 27. An energy bandgap diagram for the active layer 25 composed of the barrier layer 25a is shown.

In this diagram, more specifically, the n-type nitride semiconductor layer 23 is n-type GaN, and the p-type nitride semiconductor layer 27 is composed of a p-type AlGaN electron barrier layer 27a and a p-type GaN layer 27b. Illustrated in form.

In this embodiment, as illustrated in Fig. 1, the quantum barrier layer 25a 'adjacent to the p-type nitride semiconductor layer has a region doped with n-type impurities, that is, an n-type delta doping film D. As described, the other quantum barrier layer 25a except for the p-side quantum barrier layer 25a 'may not have a region deliberately doped with n-type impurities.

In the present embodiment, the doped region employed in the p-side quantum barrier layer is illustrated as a delta doped film, but may be formed as an n-type modulation doping region.

The adjacent quantum barrier layer 25a ′ has a delta doped film D of n-type impurities, thereby effectively suppressing p-type impurities such as Mg that can diffuse from the p-type nitride semiconductor layer 27.

In addition, the quantum barrier layer 25a 'adjacent to the p-type nitride layer is delta-doped or modulated-doped with n-type impurities to improve film quality, effectively preventing bending of multi-quantum wells due to strain, and furthermore, p-type impurities. The recombination efficiency in the quantum well layer can be guaranteed by preventing the undesired diffusion of the quantum well layer.

As a result, carrier injection efficiency is improved and recombination efficiency is improved in the quantum well layer, thereby improving luminous efficiency.

3 illustrates a form in which a plurality of delta doped films are employed as the nitride semiconductor element 40 according to another embodiment of the present invention.

4 and 3, the nitride semiconductor element 40 according to the present embodiment is similar to the previous embodiment with the n-type nitride semiconductor layer 43 and the active layer 45 sequentially formed on the substrate 41. As shown in FIG. ) And a p-type nitride semiconductor layer 47.

The n-side electrode 49a is formed in the upper region of the n-type nitride semiconductor layer 47 exposed by mesa etching, and the transparent electrode layer 48 and the p-side electrode 49b are formed on the upper surface of the p-type nitride semiconductor layer 43. It is formed in turn.

In the present embodiment, the active layer 45 has a multi-quantum well structure composed of a plurality of quantum barrier layers 45a and a plurality of quantum well layers 45b. The quantum barrier layer 45a 'adjacent to the p-type nitride semiconductor layer among the plurality of quantum barrier layers 45a is a region doped with n-type impurities and has a plurality of delta doped films D1 and D2. That is, as shown in FIGS. 3 and 4, the p-side quantum barrier layer 45a ′ may have two delta doping films D1 and D2 so as to be spaced apart from each other by a predetermined interval.

5 shows the impurity concentration distribution of the active layer 45 region A0-A1-A2-A3 adjacent to the p-type nitride semiconductor layer 47. The two delta doped films D1 and D2 employed in this embodiment can provide two peak regions where n-type impurities are distributed in high concentration in the outermost p-side quantum barrier layer 45a as shown in FIG. Can be.

The n-type impurity may be at least one selected from the group consisting of Si, Ge, Sn, and Pb. As the n-type impurity, the delta doped films D1 and D2 may be in a range of 5 × 10 ^{17 to} 1 × 10 ²⁰ / cm 3. Although not limited thereto, the p-side quantum barrier layer 45a 'is about 5 nm? It has a thickness of about 30nm, the n-type delta doped films (D1, D2) is about 10? It may have a thickness of about 40 mm 3.

These two delta doped films not only effectively suppress p-type impurities such as Mg that can diffuse from the p-type nitride semiconductor layer 47, but also prevent the film quality of the quantum barrier layer 45a 'adjacent to the p-type nitride layer. It is possible to ensure the recombination efficiency in the quantum well layer by effectively preventing the bending of the multi-quantum well due to the strain and further preventing the undesired diffusion of the p-type impurities.

Through the following examples and comparative examples to check the effect of the present invention.

( Example )

6 A pair of In _{0 .2} Ga _{0 .8} N was prepared in the nitride semiconductor light-emitting device having an active layer having a quantum well layer and a GaN quantum barrier layer and quantum barrier layer adjacent to the p-type nitride semiconductor layer are each a surface area of both sides It was formed to have a GaN film of about 3 nm, and In _x Ga _{1 - x} N of about 7 nm was formed between the interface regions. A delta doped film having a near-peak Si impurity concentration of 5 × 10 ¹⁹ / cm 3 was formed in the quantum barrier layer closest to the p-type nitride semiconductor layer, whereas the intentionally doped region was not formed in the remaining quantum barrier layer.

( Comparative example )

A nitride semiconductor light emitting device was manufactured under the same conditions as in the example, except that no additional doped region was formed in the outermost quantum barrier layer and 13N GaN was intentionally dope with other quantum barrier layers.

The changes in the internal quantum efficiency with respect to the current density of the nitride semiconductor light emitting devices according to the examples and the comparative examples thus obtained were measured. The results are shown in the graph in FIG.

In the case of the nitride semiconductor light emitting device manufactured according to the present embodiment, the quantum efficiency is slightly higher than that of the nitride semiconductor light emitting device according to the comparative example. I could confirm the fact.

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.

Claims (8)

a p-type and n-type nitride semiconductor layer and an active layer interposed between the p-type and n-type nitride semiconductor layers and a plurality of quantum barrier layers and a plurality of quantum well layers are alternately stacked,
And a region doped with n-type impurities in a p-side quantum barrier layer adjacent to the p-type nitride semiconductor layer among the plurality of quantum barrier layers.
The method of claim 1,
And the other quantum barrier layer except for the p-side quantum barrier layer having the region doped with the n-type impurity does not have a region deliberately doped with the n-type impurity.
The method according to claim 1 or 2,
And the region doped with the n-type impurity of the quantum barrier layer is at least one n-type delta doping film.
The method of claim 3,
And the n-type delta doped layer is positioned inside the p-side quantum barrier layer such that the quantum barrier layer region is provided above and below the n-type delta doped layer.
The method of claim 4, wherein
The p-side quantum barrier layer is about 5 nm? It has a thickness of about 30nm, the n-type delta doped film is about 10? A nitride semiconductor light emitting device having a thickness of about 40 GPa.
The method according to claim 1 or 2,
And a region doped with the n-type impurity of the quantum barrier layer is an n-type modulation doping region.
The method according to claim 1 or 2,
And the n-type impurity is at least one element selected from the group consisting of Si, Ge, Sn, and Pb.
The method according to claim 1 or 2
And a region doped with the n-type impurity is in the range of 5 × 10 ^{17 to} 1 × 10 ²⁰ / cm 3.

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