KR100691277B1 - Gallium nitride based light emitting diode and producing method of the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride semiconductor light emitting device, comprising: a substrate, a first conductive gallium nitride based semiconductor layer formed on the substrate, an active layer formed on the first conductive gallium nitride based semiconductor layer, and the active layer A second conductive type lower gallium nitride based semiconductor layer formed on the second conductive type lower gallium nitride based semiconductor layer, an MgN based single crystal formed on the second conductive lower gallium nitride based semiconductor, and a second conductive type formed on the polarity converting layer An upper gallium nitride-based semiconductor layer, wherein the second conductive upper gallium nitride-based semiconductor layer has a rough upper surface due to a plurality of pits formed by converting its surface into an N-polarity by the polarity conversion layer. A gallium nitride-based semiconductor light emitting device is provided.

Gallium Nitride (GaN), polarity conversion layer, MgN

Description

GALLIUM NITRIDE BASED LIGHT EMITTING DIODE AND PRODUCING METHOD OF THE SAME}

1 is a cross-sectional view showing a conventional gallium nitride-based light emitting device.

2 is a cross-sectional view showing a gallium nitride-based light emitting device according to an embodiment of the present invention.

3A to 3E are AFM images of surfaces of p-type nitride semiconductor layers grown to different thicknesses in the above-described embodiment.

4A and 4B are graphs showing the light output and the driving voltage of the light emitting device obtained from the embodiment according to the present invention, respectively.

5A and 5B are graphs showing light output and driving voltage of light emitting devices obtained from comparative examples according to the prior art, respectively.

<Code Description of Main Parts of Drawing>

21: sapphire substrate 22: n-type gallium nitride based semiconductor layer

25: active layer 26: p-type gallium nitride based semiconductor layer

27: MgN polarity conversion layer

The present invention relates to a gallium nitride-based light emitting device, and relates to a gallium nitride-based light emitting device and a manufacturing method capable of forming a rough surface to improve the light extraction efficiency in the growth process without an additional etching process.

Recently, a gallium nitride-based semiconductor light emitting device is a high output optical device capable of generating light of a wide wavelength band including short wavelength light such as blue or green, and has been greatly attracting attention in the related art. The gallium nitride-based semiconductor light emitting device is composed of a semiconductor single crystal having an Al _x In _y Ga _(1-xy) N composition formula, where 0≤x≤1, 0≤y≤1, and 0 <x + y≤1. .

In general, the light efficiency of a semiconductor light emitting device is determined by an internal quantum efficiedncy and a light extraction efficiency (also called an external quantum efficiency). In particular, the light extraction efficiency is determined by the optical factors of the light emitting device, that is, the refractive index of each structure and / or the flatness of the interface.

In particular, in terms of light extraction efficiency, gallium nitride-based semiconductor light emitting devices have fundamental limitations. That is, since the GaN layer has a larger refractive index than the external atmosphere or the substrate, the critical angle that determines the range of incident angles of light emission is small. As a result, much of the light generated from the active layer is totally reflected internally and propagates in a substantially undesired direction or is lost in the total reflection process, resulting in lowered light extraction efficiency.

In order to solve this problem, there are various ways to intentionally form irregularities on the surface of the light emitting device to lower the smoothness of the surface. US Patent No. 6,4441,403 (Announcement Date: 2002.08.27, United Epitaxy Comp.) Among the methods to improve the light extraction efficiency, a method of providing a rough surface by controlling the growth temperature without an additional surface treatment process such as etching process Is proposing.

That is, the gallium nitride-based semiconductor light emitting device 10 shown in FIG. 1 includes an n-type nitride semiconductor layer 12 sequentially formed on the sapphire substrate 11, an active layer 15 having a multi-quantum well structure, and a p-type nitride. The semiconductor layer 16 is included. Here, the lower layer 16a of the p-type nitride semiconductor layer 16 is formed under high temperature conditions similarly to other nitride layers, but the upper layer 16b is grown at a low temperature (400 to 1000 ° C). Therefore, the upper layer 16b of the p-type nitride semiconductor layer 16 is grown at a temperature outside the growth temperature at which high-quality crystals can be obtained, and thus has a rough surface v.

However, when the p-type upper nitride semiconductor layer 16b is grown, since it is grown at a low temperature, the incorporation efficiency of Mg, which is a p-type impurity, is very low, and the hole concentration is reduced. In addition, NH ₃ under low temperature growth conditions Since the cracking efficiency is reduced to increase the N-pore, which plays a similar role as the n-type impurity, the concentration of the lowered holes is canceled to greatly increase the driving voltage.

As described above, the above-described prior art is an advantageous way to improve the light extraction efficiency without the additional etching process for the uneven formation or roughening treatment, but rather there is a problem of increasing the driving voltage, which is difficult to put into practical use.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to introduce a polarization conversion layer into a predetermined region of a p-type gallium nitride based semiconductor layer and to convert the upper region into a defective N polarity with a rough surface. It is to provide a gallium nitride-based light emitting device that provides.

delete

Another object of the present invention is to provide a method of manufacturing a gallium nitride-based light emitting device for converting the upper nitride layer region into a defective N polarity by using a polarity conversion layer in order to provide a rough top surface without additional etching process.

As to solve the above technical problem, the present invention,

A substrate, a first conductivity type gallium nitride based semiconductor layer formed on the substrate, an active layer formed on the first conductivity type gallium nitride based semiconductor layer, and a second conductivity type lower gallium nitride based semiconductor layer formed on the active layer And a polarization conversion layer made of an MgN-based single crystal formed on the second conductivity type lower gallium nitride based semiconductor, and a second conductivity type upper gallium nitride based semiconductor layer formed on the polarization conversion layer. The conductive upper gallium nitride-based semiconductor layer provides a gallium nitride-based semiconductor light-emitting device characterized in that it has a rough upper surface due to the plurality of pits formed by converting its surface into an N-polarity by the polarity conversion layer.

In one embodiment, the polarity converting layer is a material satisfying the compositional formula (Al _x Ga _y In _z ) Mg _{3- (x + y + z)} N ₂ (where 0 ≦ x, z ≦ 1, 0 <y ≦ 1, 0 ≦ x + y + z <3). In contrast, the polarity conversion layer may be a material (0 <a <3) satisfying the compositional formula Si _a Mg _{3 - a} N ₂ . The polarity converting layer may be formed by MBE or MOCVD in the same manner as the other layer forming process.

In a preferred embodiment of the present invention, the second conductivity type lower gallium nitride based semiconductor layer may be a p-type AlGaN based current blocking layer, and the second conductivity type upper gallium nitride based semiconductor layer may be a p type GaN contact layer. Preferably, the polarity conversion layer may have a thickness of 10 to 100nm. Preferably, the second conductivity type lower gallium nitride based semiconductor layer has a thickness of at least 100 nm. In addition, the second conductivity type lower gallium nitride based semiconductor layer preferably has a thickness of 50 ~ 180nm.

In addition, the present invention provides a method for manufacturing a gallium nitride-based semiconductor light emitting device. The method includes forming a first conductive gallium nitride based semiconductor layer on a substrate, forming an active layer on the first conductive gallium nitride based semiconductor layer, and forming a second conductive lower portion on the active layer. Forming a gallium nitride based semiconductor layer, forming a polarization converting layer of MgN based single crystal on the second conductivity type lower gallium nitride based semiconductor, and forming a second conductive upper gallium nitride on the polarization converting layer And forming a semiconductor layer, wherein the second conductive upper gallium nitride-based semiconductor layer has a rough upper surface due to a plurality of pits formed by converting the surface to N-polarity by the polarity conversion layer.

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

2 is a cross-sectional view showing a gallium nitride-based light emitting device according to an embodiment of the present invention.

Referring to FIG. 2, a nitride including an n-type gallium nitride based semiconductor layer 22 sequentially formed on a sapphire substrate 21, an active layer 25 having a multi-quantum well structure, and a p-type gallium nitride based semiconductor layer 26 Gallium-based semiconductor light emitting device 20 is shown.

The gallium nitride based semiconductor layer 26 is divided into a p-type lower semiconductor layer 26a and a p-type upper semiconductor layer 26b. The MgN-based polarity converting layer 27 according to the present invention is formed on the p-type lower semiconductor layer 26a and affects the polarity of the p-type upper semiconductor layer 26b. That is, the polarity conversion layer 27 converts the surface of the p-type upper semiconductor layer 26b grown thereon into N polarity. Since the gallium nitride layer having such an N polar surface has a lower crystallinity than the Ga polar surface, the p-type upper semiconductor layer 26b having the N polarity has a surface in which a large number of pits V are generated.

The polarity conversion layer 27 is made of MgN-based single crystal. Specifically, the polarity converting layer is a material satisfying (Al _x Ga _y In _z ) Mg _{3- (x + y + z)} N ₂ (where 0 ≦ x, z ≦ 1, 0 <y ≦ 1, 0 ≦ x + y + z <3). In contrast, the polarity conversion layer 27 may be a material (0 <a <3) satisfying the compositional formula Si _a Mg _{3 − a} N ₂ .

The polarity converting layer 27 employed in the present invention may be grown by the same MBE or MOCVD method as the other layer forming process, and thus may be formed through a continuous growth process.

The p-type lower gallium nitride-based semiconductor layer 26a may be a p-type AlGaN-based current blocking layer, and the p-type upper gallium nitride-based semiconductor layer 26b may be a p-type GaN contact layer.

In addition, the thickness t of the polarity conversion layer 27 is preferably 10 to 100 nm. If it is less than 10 nm, it is difficult to expect a sufficient polarity conversion function, and if it exceeds 100 nm, the electrical characteristics of the p-type nitride layer 26 can be reduced.

The thickness ta of the p-type lower gallium nitride semiconductor layer 26a is preferably at least 100 nm in order to prevent the MgN polarity conversion layer 27 from affecting the active layer 25. In addition, the thickness tb of the p-type upper gallium nitride semiconductor layer 26b is preferably 50 to 180 nm. If it is less than 50 nm, it is difficult to sufficiently generate defects on the surface through polarity conversion, and if it exceeds 180 nm, the resistance may be excessively increased due to an increase in the layer thickness.

As such, in the present invention, a p-type nitride layer having a desired rough surface in the growth process may be obtained through the action of the polarity conversion layer without a surface treatment process such as an additional etching process. Since the growth of the polarity conversion layer and the p-type nitride layer is performed at a high temperature, it is possible to solve the problem of increasing the driving voltage due to the decrease in the Mg impurity concentration caused by the low temperature growth.

Hereinafter, the operation and effect of the present invention will be more easily understood by comparing the specific examples according to the present invention and the comparative example according to the related art described in FIG. 1.

( Example )

This example was carried out to confirm the surface change of the p-type nitride layer by the polarity conversion layer.

First, an n-type GaN layer, an active layer of a multi-quantum well structure, and a p-type AlGaN layer were sequentially formed on the sapphire substrate at 1.5 μm, 0.5 μm, and 0.7 μm, respectively. Five such samples were prepared. The first sample was manufactured as an LED by forming an electrode without a polarity converting layer, and in the other second to sixth samples, a 120 nm MgN-based polarity converting layer was formed on the p-type AlGaN layer. Subsequently, a p-type GaN layer is further formed on the polarity converting layer under the same conditions, and the thicknesses of the p-type GaN further grown in each sample (second to sixth samples) are 80 nm, 120 nm, 160 nm, The difference was 240 nm.

In the six sample LEDs thus obtained, the surface of the finally grown p-type GaN layer (where the first sample was a p-type AlGaN surface) was photographed by AFM. The results are shown in FIGS. 3A to 3E.

As shown in FIG. 3A, the surface of the p-type AlGaN layer without the polarity conversion layer was very smooth. However, the surface of the p-type GaN layer (thickness 80 nm) formed on the MgN-based polarity conversion layer was fine as shown in FIG. 3B. It can be seen that a large number of pits are formed. When the thickness of the p-type GaN layer was increased to 120 nm, the pit size was increased as shown in FIG. 3C. When the p-type GaN layer was formed as shown in FIG. 3D, the 160 nm-thick p-type GaN layer had a distinct hexagonal pit structure. Appeared to be a large density. Through this, it can be seen that a sufficient thickness is required to convert the polarity of the p-type GaN layer formed on the polarity conversion layer to form a defect. However, as shown in FIG. 3E, when grown at 240 nm, there is almost no improvement over the surface of FIG. 3D, and rather, the driving voltage may be increased by increasing the layer thickness. Therefore, the thickness of the p-type gallium nitride layer formed on the polarity conversion layer is preferably about 180 nm or less.

In addition, for the LEDs of six samples thus obtained, light output and driving voltage were measured, and the results are shown in FIGS. 4A and 4B.

As shown in Figure 4a, the light output is increased by about 50 to 300 in the second to fifth samples employing the MgN-based polarity conversion layer. In particular, it showed the highest increase in light output in the fourth and fifth samples where surface pits were most pronounced.

On the contrary, as shown in Fig. 4B, the driving voltage change in all samples was found to be in the measurement error range (± 0.05).

( Comparative example )

In this comparative example, as in the conventional technique described with reference to FIG.

On the sapphire substrate, an n-type GaN layer, an active layer having a multi-quantum well structure, and a p-type AlGaN layer were sequentially formed at 1.5 μm, 0.5 μm, and 0.7 μm, respectively. Three such samples were prepared. In each of the first to third samples, the p-type GaN layer was formed on the p-type AlGaN layer in the same manner except for the temperature. The growth temperatures of the p-type GaN layer in each of the first to third samples were 800 ° C, 840 ° C, and 920 ° C.

The resultant in each sample was made of LED, and the light output and driving voltage were measured, and the results are shown in FIGS. 5A and 5B.

As shown in the results of the first to third samples shown in FIG. 5A, the light output increases as the temperature grows at a lower temperature. However, as shown in FIG. 5B, the driving voltage increases with the increase in the light output. This is due to the fact that the actual hole concentration decreases due to the low temperature growth.
In contrast to the results of this prior art, the present invention has the advantage that it is possible to improve the light output without changing the driving voltage as confirmed in the embodiment (see Fig. 4b).

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

As described above, the gallium nitride-based light emitting device according to the present invention introduces a polarization converting layer into a predetermined region of the p-type gallium nitride-based semiconductor layer and converts the upper region into a defective N polarity with a large number of pits. It may have a rough surface formed. This can improve the light extraction efficiency. The manufacturing method according to the present invention has the advantage that it may not be required without an additional etching process, and may not impair device characteristics such as an increase in driving voltage.

Claims (16)

Board; A first conductivity type gallium nitride based semiconductor layer formed on the substrate; An active layer formed on the first conductivity type gallium nitride based semiconductor layer; A second conductivity type lower gallium nitride based semiconductor layer formed on the active layer; A polarity conversion layer formed of MgN-based single crystal on the second conductivity type lower gallium nitride-based semiconductor; And And a second conductive upper gallium nitride based semiconductor layer formed on the polarity converting layer, wherein the second conductive upper gallium nitride based semiconductor layer is formed by converting its surface to N polarity by the polarity converting layer. A gallium nitride-based semiconductor light emitting device characterized in that it has a rough upper surface due to the pit. The method of claim 1, The polarity conversion layer is made of a material satisfying the compositional formula (Al _x Ga _y In _z ) Mg _{3- (x + y + z)} N ₂ , where 0 ≦ x, z ≦ 1, 0 <y ≦ 1, 0 Gallium nitride-based semiconductor light emitting device, characterized in that ≤ x + y + z <3. The method of claim 1, The polarization conversion layer is made of a material satisfying the compositional formula Si _a Mg _{3 - a} N ₂ , wherein the gallium nitride-based semiconductor light emitting device, characterized in that 0 <a <3. The method of claim 1, The polarization conversion layer is gallium nitride-based semiconductor light emitting device, characterized in that formed by MBE or MOCVD method. The method of claim 1, The thickness of the polarity conversion layer is gallium nitride-based semiconductor light emitting device, characterized in that 10 to 100nm The method of claim 1, And the second conductive lower gallium nitride based semiconductor layer is a p-type AlGaN based current blocking layer, and the second conductive upper gallium nitride based semiconductor layer is a p type GaN contact layer. The method of claim 1, And the second conductive lower gallium nitride based semiconductor layer has a thickness of at least 100 nm. The method of claim 1, And a thickness of the second conductive upper gallium nitride based semiconductor layer is 50 to 180 nm. Forming a first conductivity type gallium nitride based semiconductor layer on the substrate; Forming an active layer on the first conductivity type gallium nitride based semiconductor layer; Forming a second conductivity type lower gallium nitride based semiconductor layer on the active layer; Forming a polarization conversion layer made of MgN-based single crystal on the second conductivity type lower gallium nitride-based semiconductor; And And forming a second conductivity type upper gallium nitride based semiconductor layer on the polarity converting layer, wherein the surface of the second conductivity type upper gallium nitride based semiconductor layer is converted to N polarity by the polarity converting layer. A method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that it has a rough upper surface due to the plurality of pits formed. The method of claim 9, The polarity conversion layer is made of a material satisfying the compositional formula (Al _x Ga _y In _z ) Mg _{3- (x + y + z)} N ₂ , where 0 ≦ x, z ≦ 1, 0 <y ≦ 1, 0 Gallium nitride-based semiconductor light emitting device manufacturing method characterized in that ≤ x + y + z <3. The method of claim 9, The polarity conversion layer is made of a material that satisfies the compositional formula Si _a Mg _{3 - a} N ₂ , the method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that 0 <a <3 in the composition formula. The method of claim 9, The polarization conversion layer is a method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that formed by MBE or MOCVD method. The method of claim 9, The thickness of the polarity conversion layer is a method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that 10 to 100nm. The method of claim 9, The second conductive lower gallium nitride-based semiconductor layer is a p-type AlGaN-based current blocking layer, the second conductive upper gallium nitride-based semiconductor layer is a p-type GaN contact layer manufacturing, characterized in that Way. The method of claim 9, And the thickness of the second conductive lower gallium nitride based semiconductor layer is at least 100 nm. The method of claim 9, And a thickness of the second conductive upper gallium nitride based semiconductor layer is 50 to 180 nm.

Images