KR20020079659A - AlGaInN semiconductor LED device - Google Patents

Abstract

PURPOSE: An AlGaInN semiconductor LED is provided to improve external quantum efficiency by forming n-InGaN layer on p-GaN and etching a predetermined portion of n-InGaN to make prominence and depression so that the light limited by the critical angle can be extracted. CONSTITUTION: A buffer layer(21), an n-GaN layer(22), an InGaN/GaN active layer(23), a p-GaN layer(24) and an n-InGaN crystal layer(25) are formed on an upper surface of a substrate(20) in a consecutive order. An ohmic contact electrode(27) is formed on the depressed surface after a predetermined portion of the upper surface of the n-InGaN crystal layer is etched. A p-type electrode pad(28) and an n-type electrode(26) are deposited on the transparent electrode for electrical connection to the external.

Description

Gallium nitride based semiconductor LED device {AlGaInN semiconductor LED device}

The present invention relates to an AlGaInN semiconductor LED device and a method of manufacturing the same. More particularly, the n In _x Ga _1-x N layer is formed on p-GaN and a portion of the n layer is etched to form irregularities. The present invention relates to a structure of a gallium nitride-based semiconductor device in which an electrode is formed on a lower surface, and an n-layer surface is formed into an uneven shape to dramatically improve external quantum efficiency.

In general, a GaN-based light emitting diode (LED) optical device includes a buffer layer 11, an n-type GaN layer 12, and an InGaN / GaN active layer on a sapphire substrate 10, as shown in FIG. 1. 13), a p-type GaN layer 14, a transparent electrode 15 on the front surface, an n-type metal electrode 16 and a p-type metal electrode 17, the buffer layer on the sapphire substrate 10 ( 11) after the n-type GaN layer 12, the InGaN / GaN active layer 13, and the p-type GaN layer 14 are grown in sequential order, a portion of the n-type metal electrode 16 is formed to form the n-type metal electrode 16. It is formed by etching to the GaN layer 12, forming a transparent electrode 15 on the entire surface of the p-type GaN, and then depositing the n-type metal electrode 17 and the p-type metal electrode 18.

As shown in FIG. 1, since the resistivity of p-GaN is very high, conventional LEDs employ various kinds of transparent ohmic electrodes 15 such as NiAu to facilitate current spreading. These transparent electrodes generally have a thickness of several nm to several tens of nm, and increasing the thickness reduces the lateral series resistance of the p-GaN layer, but the light transmittance of the metal electrode is lowered, so that the light emitted to the upper side reduces the external quantum efficiency. This decreases. The transmittance of the transparent electrode is usually 60 to 80% depending on the thickness and the degree of change of the process. In this case, 20% ~ 40% of the light to be emitted to the upper side has a disadvantage that can not be emitted over the chip.

In addition, the light efficiency of the LED is divided into internal quantum efficiency and external quantum efficiency, and the internal quantum efficiency is determined by the design and quality of the active layer. In the case of external quantum efficiency, the light generated from the active layer is determined according to the degree to which the chip comes out of the chip. In the case of GaN material or sapphire with a constant refractive index, it is necessary to cross the critical angle in order for the light to flow into the air having a refractive index of 1. Figure 2 shows the refractive angle according to the refractive index of each material between GaN and air or resin having different refractive index. As shown in the figure, the critical angle qc = sin-1 (n _low / n _high ) with escape angle θ2 = 90 degrees, and when the light travels from GaN into the air above the chip, the critical angle is about 23.6 degrees. Light generated at more angles is returned to the inside of the chip, and the light is confined inside the chip and absorbed in the epi layer or the sapphire wafer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to form an n InxGa _(1-x) N layer on p-GaN and to form an unevenness by etching a portion of the n InGaN layer. The present invention relates to a structure of a gallium nitride-based semiconductor LED device in which an n-type transparent ohmic electrode is formed on a bottom surface and a shape formed on an n-layer surface is extracted to the outside, thereby greatly improving external quantum efficiency.

1 is a cross-sectional view showing the structure of a conventional GaN-based semiconductor optical device.

2 is a diagram illustrating the escape angle of light in the GaN layer.

3 is a cross-sectional view showing the structure of an AlGaInN semiconductor optical device according to the present invention;

4 is a detailed cross-sectional view illustrating the structure of the n-layer according to the present invention.

5 is an energy band diagram for explaining the principle of operation of the n layer and p layer according to the present invention.

<Description of the code | symbol about the principal part of drawing>

10, 20. Substrate 11, 21. Buffer layer

12, 22.n-GaN layer 13, 23.InGaN / GaN active layer

14, 24, 34.p-GaN layer 15, 27, 37. transparent electrode

25, 35. n InGaN layer 16, 26. n-type metal electrode

17, 28. p-type metal electrode 39. Optical path

In order to achieve the above object, the gallium nitride based semiconductor device according to the present invention is a GaN based semiconductor device having an npn junction diode structure, wherein n has a predetermined thickness on top of a P-GaN layer, which is the top layer of a conventional semiconductor LED device. A type InGaN / GaN crystal layer is formed, and a portion of the n layer is processed to form an ohmic electrode on the n layer, and the surface is rugged, thereby improving the external quantum efficiency.

Referring to the LED device according to the present invention in detail based on the accompanying drawings as follows.

3 is a cross-sectional view illustrating a structure of a semiconductor optical device according to the present invention.

As shown in FIG. 3, the present invention is a GaN-based semiconductor optical device having an npn diode structure, unlike a conventional pn-type structure, and includes a buffer layer 21, an n-GaN layer 22, and InGaN / on a substrate 20. The GaN active layer 23, the p-GaN layer 24, and the n In _x Ga _(1-x) N crystal layer 25 are sequentially formed, and then the n In _x Ga _(1-x) N layer 25 A portion of the n layer of the top surface is etched away, leaving a portion of the n layer to be of a predetermined thickness, where n charges remaining at the predetermined thickness are thinned below the n layer with the n-ohm contact metal formed on the n layer. Forming an ohmic contact transparent electrode 27 on the configured n and forming a p-type electrode pad 28 for electrical connection to the outside on the transparent electrode and forming a portion of the n layer and a portion of the p layer, and an active layer A portion is etched and n-type electrode 26 is formed on the n-GaN layer.

The n In _x Ga _1-x N (O ≦ _x ≦ ₁ ) crystal layer 25 is grown to a thickness of about 1.0 nm ≦ t ≦ 10,000 nm, and the n doping concentration is 10 ¹⁷ / cm ³ <n <10 ²³ / cm ³ .

4 shows a detailed cross-sectional view after forming the ohmic contact type transparent electrode 27 on the thinly configured n. It has been shown that the external quantum efficiency can be improved by etching a part of the n layer to form an uneven surface to increase the effective angle of light escape of the light emitted from the active layer.

FIG. 5 shows an energy band diagram in cross section B-B 'of FIG. 3, illustrating a principle of tunnel junction composed of an n In _x Ga _1-x N (0 ≦ _x ≦ 1) layer, a metal electrode, and a p layer. Doing. When a positive voltage is supplied to the metal electrode, a thin n In _x Ga _1-x N (0 ≦ _x ≦ 1) layer is formed in order for a hole to progress to the p GaN layer due to a tunnel phenomenon.

As described above, the present invention is a semiconductor device having a new structure that significantly improves external quantum efficiency. As shown in Figure 2 has a structure to improve the light emission efficiency to the upper side of the chip by minimizing the area of the transparent electrode having about 60 ~ 80%. In addition, as shown in FIG. 3, the surface of the chip has an uneven shape to increase the effective angle of light escape of the light emitted from the active layer, thereby improving the external quantum efficiency.

According to the present invention made as described above, an n In _x Ga _1- xN (0 ≦ _x ≦ ₁ ) layer is formed on the p-GaN layer and an n In _x Ga _1-x N (0 ≦ _x ≦ 1) layer. Is partially etched so that a predetermined n In _x Ga _1-x N (0≤x≤1) layer remains, and a transparent metal electrode is formed on the thinly left n In _x Ga _1-x N (0≤x≤1) layer. To maximize the external emission of light by minimizing the area of the transparent electrode, and to supply holes to the p-GaN through the n-layer from the n-metal electrode by tunneling, thereby forming a direct ohmic contact on the p-layer. Power consumption can be reduced by driving at a lower operating voltage, and the surface of the n In _x Ga _1-x N (0≤x≤1) layer is formed into a concave-convex shape, thereby modifying the exit angle of the light so that the upper portion of the chip in the active layer By maximizing the amount of light emitted, the external quantum efficiency can be dramatically improved.

Claims (9)

In a GaN-based semiconductor device having an n-p-n junction diode structure, An n-layer In _x Ga _1-x N (0≤x≤1) layer is formed on top of the p-GaN layer, which is the top layer of the semiconductor device, and a portion of the n layer is etched to leave a predetermined n layer and thin. Form a transparent n-ohm metal junction on the remaining n In _x Ga _1-x N (0≤x≤1) to uneven the surface of the unetched n In _x Ga _1-x N (0≤x≤1) layer. A semiconductor device that has been shaped to maximize the amount of light emitted from the active layer to the top of the chip. The In composition x of In _x Ga _1-x N on top of the p layer is made smaller than _z in the active layer In _z Ga _1-z N, ie x <z. The method of claim 1, wherein the n In _x Ga _1-x N (0 ≦ _x ≦ 1) crystal layer is formed to have a thickness h2 of 1.0 to 10,000 nm before etching. The n InGaN layer (h1) remaining after etching is formed to a thickness of 0.5 to 100nm. The gallium nitride based LED semiconductor device according to claim 1, wherein the doping concentration of n InGaN is set to 10 ¹⁷ to 10 ²³ / cm ³ . The width d1 of the unevenness is formed in a range of 100 nm to 100,000 nm. The method of claim 1, wherein the width (d2) of the etched portion is formed to 100nm ~ 100,00nm. In a GaN-based semiconductor device having an n-p-n junction diode structure, An n-layered In _z Ga _1-z Nz (0 ≦ _z ≦ 1) layer is formed on top of the p-GaN layer, which is the top layer of the semiconductor device, and n-layered In _y Ga _1-y having different indium content. N (0≤y≤1) layers are grown in sequence, and a portion of the upper n In _y Ga _1-y N (0≤y≤1) layer is selectively etched to lower n In _z Ga _1-z N ( Leaving a layer of 0≤z≤1) and forming a transparent n-ohm metal junction on the thin n In _z Ga _1-z N (0≤z≤1) to minimize the area of the transparent electrode, and n In _y Ga A semiconductor device in which the surface of the _1-y N (0 ≦ _y ≦ 1) layer is formed into an uneven shape to maximize the amount of light emitted from the active layer to the top of the chip. 9. The method of claim 8, wherein the upper n In _y Ga1- _y N (0≤y≤1) crystal layer is formed to a thickness of 1.0 ~ 10,000 nm, the lower n In _z Ga _1-z Nz (0≤z≤ 1) A layer is formed with a thickness of 1.0-100nm, gallium nitride-based LED semiconductor device characterized in that the doping concentration of the two n-layer to 10 ¹⁷ ~ 10 ²³ / cm ³ to form.