KR101165253B1 - Light emitting diode - Google Patents

Abstract

A light emitting diode comprising a substrate, an n-type semiconductor layer, an active layer and a p-type semiconductor layer formed on the substrate, and a transparent electrode layer formed on the p-type semiconductor layer is disclosed. The transparent electrode layer includes an opening that exposes the p-type semiconductor layer, and includes a current blocking unit formed in the opening and an electrode pad formed on the current blocking unit.

Description

[0001] LIGHT EMITTING DIODE [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light emitting diodes, and more particularly to gallium nitride based light emitting diodes, and more particularly, to light emitting diodes having improved current diffusion efficiency and light extraction efficiency through improvement in the vicinity of electrode pads.

The light emitting diode is a photoelectric conversion element in which electrons and holes meet and emit light by a P-N semiconductor junction (P-N junction) by applying current. For example, a GaN-based light emitting diode in which an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are sequentially formed on a substrate is known. A transparent electrode layer is formed on the p-type semiconductor layer, and a p-type electrode pad is formed on the transparent electrode layer. In addition, the active layer and a portion of the p-type semiconductor layer thereon may be removed to expose a portion of the n-type semiconductor layer upwards. In this case, an n-type electrode pad is formed in an upper region of the exposed n-type semiconductor layer. .

In the light emitting diode as described above, the transparent electrode layer is a portion which functions as an electrode together with an electrode pad formed thereon, and is a portion in which light is mainly emitted. Therefore, the transparent electrode layer is required to have excellent electrical characteristics and characteristics that do not inhibit light emission. As the transparent electrode layer, a Ni / Au layer and an ITO (indium tin oxide) layer are known, but the Ni / Au layer has excellent electrical properties but has a disadvantage of low transmittance to visible light. In addition, the ITO layer has an advantage that the transmittance of visible light is more than 90% and excellent in light transmittance, but has a problem in that electrical properties are inferior.

One example of a conventional light emitting diode is to form an opening by etching a part of a transparent electrode layer (especially an ITO layer), and the p-type electrode pad is in contact with the p-type semiconductor layer through the opening. Such a conventional light emitting diode forms a p-type tunnel layer (p ++) doped with a high concentration of p-type impurities on a p-type semiconductor layer for ohmic contact, and thus, the p-type electrode pad is p Contact with the tunnel tunnel layer.

The above-described conventional light emitting diode has a problem in that current flows under the p-type electrode pad so that current does not spread widely on the transparent electrode layer. This is due to the structure in which the p-type electrode pad and the p-type tunnel layer are in direct contact with each other, and may reduce the recombination rate of electrons and holes in the active layer, thereby causing a decrease in luminous efficiency. In addition, the conventional light emitting diode has a problem in that light is absorbed by the p-type electrode pad and the light loss is large.

Accordingly, a technical problem of the present invention is to provide a light emitting diode under a p-type electrode pad having a distributed bragg reflector (DBR) capable of reducing light absorption and thereby light loss and diffusing light to its surroundings. To provide.

According to one aspect of the invention, there is provided a light emitting diode comprising an n-type semiconductor layer, an active layer, a p-type semiconductor layer and a transparent electrode layer. The light emitting diode includes an opening formed in the transparent electrode layer to expose the tunnel layer interposed between the p-type semiconductor layer and the transparent electrode layer, and the tunnel layer or a p-type semiconductor layer below the upper side, and in the opening. And an electrode pad formed on the transparent electrode layer to cover the DBR formed in the opening. In this case, the light emitting diode is preferably gallium nitride.

Preferably, the side surface portion of the electrode pad contacts the inner surface of the opening of the transparent electrode layer, and the bottom portion of the electrode pad contacts the DBR.

Preferably, the tunnel layer is an n-type tunnel layer (n ++) doped with a high concentration of n-type impurities.

Preferably, the transparent electrode layer is an ITO layer.

Preferably, the light emitting diode further includes a lower DBR formed on the bottom surface of the active layer.

According to the present invention, the DBR reflects the light directed to the electrode pad with high reflection efficiency, thereby minimizing light loss due to light absorption of the electrode pad, thereby increasing the light extraction efficiency. In addition, the present invention prevents direct current from flowing from the electrode pad to the p-type semiconductor layer or the tunnel layer thereon, thereby increasing the current diffusion efficiency in the transparent electrode layer, thereby improving the luminous efficiency of the light emitting diode. have.

1 is a cross-sectional view showing a light emitting diode according to an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view illustrating a DBR structure of the light emitting diode shown in FIG. 1. FIG.
3 is a cross-sectional view showing a light emitting diode according to another embodiment of the present invention.
4 is a cross-sectional view showing a light emitting diode according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

1 is a cross-sectional view showing a light emitting diode according to an embodiment of the present invention, Figure 2 is an enlarged cross-sectional view showing the structure of a DBR according to an embodiment of the present invention.

Referring to FIG. 1, the light emitting diode 1 of the present embodiment includes a substrate 100, an n-type semiconductor layer 220, an active layer 240, and a p-type semiconductor layer 260 formed on the substrate 100. ). The active layer 240 is interposed between the n-type semiconductor layer 220 and the p-type semiconductor layer 260, the transparent electrode layer 320 is formed on the upper surface of the p-type semiconductor layer 260. In addition, a portion of the active layer 240 and the p-type semiconductor layer 260 may be removed, and a portion of the n-type semiconductor layer 220 may be exposed upward. A p-type electrode pad 340 may be formed on an upper surface of the transparent electrode layer 320, and an n-type electrode pad 440 may be formed on an upper surface of the n-type semiconductor layer 220.

The substrate 100 may be a sapphire (Al ₂ O ₃ ) substrate or a SiC substrate having a higher thermal conductivity than the sapphire substrate. A buffer layer 210 may be formed on the substrate 100 to mitigate lattice mismatch with the n-type semiconductor layer 200. The semiconductor layers formed on the substrate 100 may be GaN-based, and the buffer layer 210 may be AlN or GaN.

The active layer 240 is limitedly formed on a portion of the n-type semiconductor layer 220, and the p-type semiconductor layer 260 is formed on the active layer 240. Accordingly, a portion of the upper surface of the n-type semiconductor layer 220 is in contact with the active layer 240, and the remaining portion of the upper surface of the n-type semiconductor layer 220 is partially removed by the partial removal of the p-type semiconductor layer 260 and the active layer 240 described above. Is exposed. As the transparent electrode layer 320 above the p-type semiconductor layer 260, an ITO transparent electrode layer made of indium tin oxide having good transmittance of visible light is used.

The n-type semiconductor layer 220 may be formed of _{Al x In y Ga 1 -x- y} N (0≤x, y, x + y≤1) of n-type, can include a N-type clad layer have. In addition, the p-type semiconductor layer 260 may be formed of p-type Al _x In _y Ga _1-xy N (0 ≦ x, y, x + y ≦ 1), and may include a p-type cladding layer. . The n-type semiconductor layer 220 may be formed by doping silicon (Si), and the p-type semiconductor layer 260 may be formed by doping zinc (Zn) or magnesium (Mg).

In addition, the active layer 240 is an area where electrons and holes are recombined, and may include InGaN. The wavelength of the extracted light is determined according to the type of the material forming the active layer 240. The active layer 240 may be a multilayer film in which a quantum well layer and a barrier layer are repeatedly formed. The barrier layer and the well layer may be binary to quaternary compound semiconductor layers represented by general formula Al _x In _y Ga _{1 −x− y} N (0 ≦ x, y, x + y ≦ 1).

According to a preferred embodiment of the present invention, a tunnel layer 310 is formed between the ITO transparent electrode layer 320 and the p semiconductor layer 260 thereunder. The tunnel layer 310 allows an ohmic contact to be formed between the ITO transparent electrode layer 320 and the p-type semiconductor layer 260. In this case, the tunnel layer 310 is composed of an n + + tunnel layer doped with n-type impurities at high dynamics. In an embodiment of the present invention, as the material of the tunnel layer 310, n ++ In _{1 - x} Al _{1 - y} Ga _{1 - z} N (0≤x≤1, 0≤y≤1, 0≤z≤1) Use

In addition, an opening 342 is formed in the ITO transparent electrode layer 320 to expose a portion of the tunnel layer 310 upward. The opening 342 is formed by etching a portion of the ITO transparent electrode layer 320. For the etching, the remaining transparent electrode layer 320 except for the place where the opening 342 is formed is covered with a mask material such as, for example, a photoresist (PR), and then a portion corresponding to the opening 342 is removed. An etching process is performed, which may be wet or dry etching. According to a preferred embodiment of the present invention, the opening 342 exposes a portion of the tunnel layer 310, but is formed in the opening 342 by the etching to form a p-type under the tunnel layer 310. It may also be considered that the semiconductor layer 260 is exposed upward by the opening 342.

In addition, a distributed bragg reflector (DBR) 330 is formed at a predetermined height in the opening 342. The DBR 330 is formed by filling the opening 342 to a predetermined height on the upper surface of the tunnel layer 310. The bottom surface of the DBR 330 is in contact with the top surface of the tunnel layer 310, and the top surface is in contact with the p-type electrode pad 340 formed on the ITO transparent electrode layer 320. The electrode pad 340 may be made of metal such as nickel (Ni), chromium (Cr), platinum (Pt), gold (Au), silver (Ag), titanium (Ti), tungsten (W), or carbon nanotubes. Can be used.

The electrode pad 340 as described above has its bottom surface in contact with the upper surface of the DBR 330 in the opening 342, and the ITO transparent electrode layer 320 in the inner surface of the opening 342. . Further, the electrode pad 340 is in contact with the ITO transparent electrode layer 320 even outside the opening 342.

The DBR 330 blocks an electric current flowing directly from the electrode pad 340 to the tunnel layer 310 between the electrode pad 340 and the tunnel layer 310, thereby preventing the ITO transparent electrode layer 320. Enables wide current spreading at In addition, the DBR 330 has a structure in which the light reflectance is much larger than that of the metal forming the electrode pad 340, thereby minimizing light absorption and loss of light by the electrode pad 340. A light emitting diode that imparts a current spreading function under the electrode pad 340 is disclosed in Patent Registration No. 10-0721515, registered by the applicant, which is incorporated herein by reference.

When λ is a wavelength of light, n is a refractive index of a medium, and m is odd, the DBRs 330 are alternately stacked with a thickness of mλ / 4n to obtain a reflectance of 95% or more in light of a specific wavelength band λ. Semiconductor laminate structure. The DBR 330 has a bandgap energy greater than the oscillation wavelength, so that absorption of light does not occur well, and the reflectance may be increased by increasing the refractive index between the layers (ie, media) of the DBR 330.

Referring to FIG. 2, the DBR 330 has a structure in which a lamination structure of the low refractive index layer 330a and the high refractive index layer 330b is sequentially and repeatedly stacked. In this case, the low refractive index layer 330a and the high refractive index layer 330b have a λ / 4 thickness of a reference wavelength. Various materials may be considered as the material of the low refractive index layer 330a and the high refractive index layer 330b. Preferably, the low refractive index layer 330a includes SiO ₂ having a refractive index of 1.4 or Al ₂ having a refractive index of 1.6. O ₃ is used, and as the high refractive index layer 330b, Si ₃ N ₄ or TiO ₂ having a refractive index of 2 or more or Si-H having a refractive index of 3 or more is used.

3 is a view showing a light emitting diode according to another embodiment of the present invention. Referring to FIG. 3, the light emitting diode 1 of the present embodiment includes a DBR 330 (hereinafter referred to as “upper DBR”) formed between the electrode pad 340 and the tunnel layer 310 in the opening 342. On the other hand, it further includes a DBR 230 (hereinafter referred to as "lower DBR") formed on the bottom surface of the active layer 240. Since the structure of the lower DBR 230 is the same as or similar to that of the upper DBR 330 described with reference to FIG. 2, a detailed description thereof will be omitted.

In the light emitting diode 1 shown in FIG. 3, the light indicated by arrow A generated from the active layer 240 and the light indicated by arrow B reflected by the upper DBR 330 are reflected by the lower DBR 230. To the top. In this case, the lower DBR 230 improves the light extraction efficiency of the light emitting diode by its high reflectance, and also moves light in the light emitting diode, compared to the conventional light emitting diode in which light is reflected by a reflecting material below the substrate. The distance can be reduced, and thereby the light extraction efficiency of the light emitting diode can be improved.

4 is a view illustrating a light emitting diode 1 according to another embodiment of the present invention, wherein an opening 342 is formed in the transparent electrode layer 320, and an electrode pad 340 is formed in the opening 342. The bottom surface of the electrode pad 340 is formed on the p-type semiconductor layer 260 and is in contact with the electrode pad 340 and the layer 330 ′ capable of ohmic contact. The layer 330 ′ may be an n ++ layer heavily doped with n-type impurities, or may be undoped InGaN. In this case, the DBR described as located in the opening 342 may be omitted.

100: substrate 220: n-type semiconductor layer
240: active layer 260: p-type semiconductor layer
320: transparent electrode layer 340: p-type electrode pad
310: tunnel layer 342: opening
330: DBR

Claims (7)

Board;
An n-type semiconductor layer, an active layer and a p-type semiconductor layer formed on the substrate; And
It includes; a transparent electrode layer formed on the p-type semiconductor layer,
The transparent electrode layer includes an opening exposing the p-type semiconductor layer,
A light emitting diode comprising a DBR formed in the opening and an electrode pad formed on the DBR. The method of claim 1,
The DBR is a light emitting diode comprising SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ or TiO ₂ . delete The method of claim 1,
The DBR has a light reflectance greater than that of an electrode pad. The method of claim 1,
The DBR has a structure in which a low refractive index layer and a high refractive index layer are continuously stacked repeatedly,
The low refractive index layer is SiO ₂ or Al ₂ O ₃ is used,
The high refractive index layer is a light emitting diode, characterized in that Si ₃ N ₄ or TiO ₂ is used. The method of claim 1,
The side surface portion of the electrode pad is in contact with the inner surface of the opening of the transparent electrode layer. The method according to claim 6,
The electrode pad is in contact with the transparent electrode layer from the outside of the opening.

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