KR101483230B1 - Nitride Semiconductor Light Emitting Device - Google Patents

Abstract

The present invention relates to a nitride semiconductor light emitting device having improved light transmittance and ohmic contact characteristics of a p-side transparent electrode. A nitride semiconductor light emitting device according to one aspect of the present invention includes: a light emitting structure including an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer sequentially formed on a substrate; And an In ₂ O ₃ layer doped with at least one of Mg, Cu and Zn formed on the p-type nitride semiconductor layer and a transparent conductive oxide (TCO) formed on the doped In ₂ O ₃ layer, And nano dots of a solid solution containing at least one of Mg, Cu, and Zn and Ga are formed at an interface between the p-type nitride semiconductor layer and the doped In ₂ O ₃ layer .

Nitride semiconductor, LED

Description

[0001] NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE [0002]

The present invention relates to a nitride semiconductor light emitting device, and more particularly, to a nitride semiconductor light emitting device that improves the transmittance of a p-side transparent electrode structure and improves an ohmic contact property with a p-type nitride semiconductor .

After the development of nitride semiconductor light emitting devices (e.g., Group III nitride compound semiconductor LEDs or laser diodes), nitride semiconductor light emitting devices have attracted attention as a main light source in the next generation in various fields such as display backlight, camera flash, and illumination . 2. Description of the Related Art As an application field of a nitride semiconductor light emitting device has expanded, efforts have been made to increase brightness and luminous efficiency.

Blue LEDs using nitride based compound semiconductors such as GaN, InGaN, AlGaN, or AlInGaN have advantages of being capable of realizing full colors, but they are usually grown on a sapphire substrate which is an insulator. Therefore, unlike light emitting diodes using conventional conductive substrates the n-electrode and the p-electrode are disposed on the same side (on the crystal-grown nitride semiconductor), and accordingly, the light-emitting area becomes small. Since a p-type nitride semiconductor such as p-GaN has a large work function and a high resistance, it is impossible to use a p-electrode (bonding pad or electrode pad) metal directly on the p-type nitride semiconductor, spreading target metal is deposited on the p-type nitride semiconductor. A method of forming an ohmic contact by depositing a Ni / Au thin film on a p-type nitride semiconductor and subjecting it to heat treatment has been proposed.

1 is a cross-sectional view of a conventional nitride semiconductor light emitting device. 1, the nitride semiconductor light emitting device 10 includes an n-type nitride semiconductor layer 12, an active layer 13, and a p-type nitride semiconductor layer 14 sequentially formed on a sapphire substrate 11. The n-type nitride semiconductor layer 12 may be composed of an n-type GaN layer 12b and an n-type AlGaN layer 12a. The p-type nitride semiconductor layer 14 may include a p-type GaN layer 14b and a p- (14a). a GaN buffer layer (not shown) may be formed between the n-type nitride semiconductor layer 12 and the substrate 11 for lattice matching therebetween. An n-electrode or n-side electrode pad 16 is formed on the n-type GaN layer 12b exposed by mesa etching. Since the p-type nitride semiconductor layer 14 has a relatively high resistance, the additional p-type nitride semiconductor layer 14 can form an ohmic contact with the p-type nitride semiconductor layer 14 before forming the p- Layer is required. A method of forming a transparent electrode 15 made of Ni / Au as an additional layer for this ohmic contact has been proposed.

However, since the transparent electrode 15 made of Ni / Au has a low transmittance of about 60 to 70% even after heat treatment, it can not effectively transmit the light emitted from the active layer. Accordingly, when the package is implemented by wire bonding using the light emitting device, the overall luminous efficiency of the light emitting device is lowered due to the low transmittance of Ni / Au.

In order to solve the problems described above, there is proposed a method of increasing the light transmittance of a light emitting diode using indium tin oxide (ITO) or ZnO, which is known to have a transmittance of 90% or more, instead of a transmissive film using Ni / Au. However, due to the difference in work function between a p-type nitride semiconductor (having a work function of about 7.5 eV) such as p-GaN and ITO (having a work function of 4.7 to 5.2 eV), ITO formed through direct deposition on the p- The transparent electrode does not form an ohmic contact well with the p-type nitride semiconductor.

Thus, in order to reduce the difference in work function at the interface between the p-type nitride semiconductor and the transparent electrode to form an ohmic contact, a material having a low work function such as Zn is doped on the surface portion of the p-type GaN layer 14b, Carbon) is doped at a high concentration to reduce the work function of the p-type GaN semiconductor and to deposit ITO thereon. However, since doped Zn or C has high mobility, it diffuses under the p-type GaN layer when using the light emitting element for a long time, and may adversely affect the reliability of the light emitting element. In addition, there is a problem in that a complicated process is required to change the GaN growth process.

An object of the present invention is to provide a nitride semiconductor light emitting device having a transparent electrode structure that has high light transmittance and forms a good ohmic contact with a p-type nitride semiconductor, thereby improving a contact resistance problem .

A nitride semiconductor light emitting device according to one aspect of the present invention includes: a light emitting structure including an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer sequentially formed on a substrate; And an In ₂ O ₃ layer doped with at least one of Mg, Cu and Zn formed on the p-type nitride semiconductor layer and a transparent conductive oxide (TCO) formed on the doped In ₂ O ₃ layer, And nano dots of a solid solution containing at least one of Mg, Cu, and Zn and Ga are formed at an interface between the p-type nitride semiconductor layer and the doped In ₂ O ₃ layer .

The TCO layer may be at least one conductive oxide selected from indium tin oxide (ITO), zinc oxide (ZnO), and magnesium oxide (MgO). On the p-type nitride semiconductor layer, the nano dots may be filled with the doped In ₂ O ₃ layer.

According to the embodiment of the present invention, the nitride semiconductor light emitting device is formed on the TCO layer and includes at least one metal layer selected from the group consisting of Ag, Pt, Au, Co, Ir and an additional TCO layer As shown in FIG. This metal layer / stack of additional TCO layers may be stacked one or more times in succession. The metal layer may have a thickness of 1 to 10 angstroms.

According to an embodiment of the present invention, the nitride semiconductor light emitting device is formed between the doped In ₂ O ₃ layer and the TCO layer and includes at least one metal layer selected from the group consisting of Ag, Pt, Au, Co, As shown in FIG.

The doped In ₂ O ₃ layer may have a thickness of 10-200 Å or less. The TCO layer may have a thickness of 1000 to 6000 ANGSTROM.

The nano-dots may include Ga in the nitride semiconductor layer and Mg, Cu, or Zn in the doped In ₂ O ₃ layer by heat treatment on the doped In ₂ O ₃ layer and the TCO layer formed on the p- Or may be a eutectic formed through a chemical reaction between the two.

According to the present invention, since the Schottky barrier at the interface portion is lowered by at least one of Mg, Cu, Zn formed in the interface between the doped In2O3 layer and the p-type nitride semiconductor layer and the Ga interstitial material, The characteristics are improved and the current diffusion effect is increased. Further, by using the transparent electrode structure described above, a high light transmittance can be secured. This lowers the forward voltage (Vf) of the nitride semiconductor light emitting device and increases the luminance and luminous efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The shape and the size of the elements in the drawings may be exaggerated for clarity and the same elements are denoted by the same reference numerals in the drawings.

2 is a cross-sectional view of a nitride semiconductor light emitting device according to an embodiment of the present invention. 1, the nitride semiconductor light emitting device 100 includes an n-type nitride semiconductor layer 102, an active layer 103, and a p-type nitride semiconductor layer 104 formed on a substrate 101 such as sapphire. The n-type and p-type nitride semiconductor layers 102 and 104 and the active layer 103 interposed therebetween constitute a semiconductor light emitting structure. A buffer layer 120 for lattice matching is formed between the substrate 101 and the n-type nitride semiconductor layer 103.

An n-electrode or n-electrode pad 108 is formed on the exposed n-type nitride semiconductor layer 102 by mesa etching. On the p-type nitride semiconductor layer 107, an In ₂ O ₃ layer 115 doped with at least one of Mg, Cu and Zn as a p-side transparent electrode structure and a transparent conductive oxide layer (hereinafter referred to as "TCO &Quot; layer (also referred to as a "layer ") 116 is formed, and a p-side electrode pad or bonding pad 107 is formed thereon. This transparent electrode structure also includes nano dots 125 formed in the interface between the p-type nitride semiconductor layer 104 and the doped In ₂ O ₃ layer.

The n-type nitride semiconductor layer 102 may include an n-type GaN layer 102b and an n-type AlGaN layer 102a. The active layer 105 may have a multiple quantum well (MQW) structure in which two or more quantum wells and a quantum barrier are stacked, or may have a single quantum well structure. For example, the active layer 105 may have a MQW structure in which InGaN / GaN is continuously stacked. The p-type nitride semiconductor layer 104 may include a p-type GaN layer 104b and a p-type AlGaN layer 104a. These nitride semiconductor layers 102, 103, and 104 may be grown using MOCVD. The buffer layer 120 for lattice matching between the nitride semiconductor crystal and the substrate may be formed of, for example, a GaN nucleation layer.

The p-side transparent electrode structure formed between the p-type nitride semiconductor layer 104 and the p-electrode 107 is composed of an In 2 O 3 layer 115 doped with at least one of Mg, Cu, and Zn, a TCO layer 116 such as ITO, and nano dots 125 formed in the interface between the p-type nitride semiconductor layers 104. The doped In ₂ O ₃ layer 115 may have a thickness of 10-200 Å or less and the TCO layer 116 may have a thickness of 1000-6000 Å.

The transparent electrode structures 115, 116 and 125 are formed on the p-type GaN layer 104b between the p-electrode 107 and the p-type GaN layer 104b having a high work function (about 7.5 eV) Thereby enhancing the current diffusion effect and simultaneously maintaining the transmittance of a certain level or higher to increase the efficiency and brightness of the light emitting device.

The TCO layer 116 may be formed of at least one of ITO, ZnO, and MgO. The TCO material has a good transmittance, but is weak in adhesion to the nitride semiconductor crystal, and has a work function significantly lower than that of the p-type GaN layer 104b It is difficult to form an ohmic contact with the p-type GaN layer 104b. In contrast, in the present embodiment, an In 2 O 3 layer 115 doped with at least one of Mg, Cu, and Zn is formed between the TCO layer 116 and the p-type nitride semiconductor layer 104 to allow ohmic contact, . In addition, ohmic contact characteristics can be increased and contact resistance can be lowered by using at least one of Mg, Cu, and Zn formed at the interface with the p-type nitride semiconductor layer and nano dots 125 of Ga interstitial solid. The nano dots 125 are filled with the doped In ₂ O ₃ layer 115 on the p-type GaN layer 104 _b .

Nanodots are there by heat treatment of the doped In ₂ O ₃ layer 115 and TCO layer 116 may be generated in the nitride bandochegwa interface, such heat treatment In ₂ O dopant in the _third layer (Mg, Cu or Zn ) And Ga in the nitride semiconductor are formed through a chemical reaction. More specifically, after the p-type nitride semiconductor layer 104 is formed, In ₂ O ₃ (115) doped with Mg, Cu or Zn is formed. Thereafter, the ITO layer 116 is deposited and then heat-treated in an N ₂ atmosphere or an air atmosphere at a temperature of 200 ° C. or higher, preferably 200 ° C. to 800 ° C., so that the p-type nitride semiconductor layer 104 (Mg, Cu or Zn) in the In ₂ O ₃ layer 115 react with each other to form the eutectic solid solution. This solution forms nano-sized nano-dots. The nano dot 125 made of a solid solution of Ga and a dopant (Mg, Cu or Zn) selectively lowers the Schottky barrier at the interface between the p-side transparent electrode structure and the nitride semiconductor as described later, .

3 is a schematic view showing energy band structures of main parts including the transparent electrode structures 115 and 116. FIG. In Fig. 3, reference symbol Ec denotes the edge of the conduction band, and reference symbol E denotes the potential energy of the electron (charge carrier). 3, in order to allow current to flow in the light emitting device, the energy barrier between the p-electrode and the p-type nitride semiconductor must be exceeded. The work function of the doped In ₂ O ₃ layer and the TCO layers 115 and 116 (? _A ,? _B ) of nano-dots 125 made of a solid solution of at least one of Mg, Cu, Zn and Ga is larger than the work function? _X. Accordingly, the nano dot 125 selectively lowers the Schottky barrier at the interface between the transparent electrode structure and the p-type nitride semiconductor. As a result, the ohmic characteristics of the transparent electrode structure are improved and the contact resistance is lowered, resulting in an improvement in the electrical characteristics of the light emitting device and an increase in the current diffusion effect (see FIGS. 6B, 7A and 7B).

In addition, since most or substantially all of the transparent electrode structure is formed of a TCO material such as ITO and In ₂ O ₃ , the light transmittance of the entire p-side transparent electrode structure is considerably higher than that of conventional transparent electrode structures such as Ni / Au (See Figs. 6A, 7A and 7B). As a result of the experiment, it was confirmed that the transmittance of Ni / Au was improved by about 20 ~ 30% by using the above-mentioned transparent electrode structure.

4 is a cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention. In the light emitting device 200 of FIG. 4, a metal layer such as Ag is inserted in the TCO layer to a thickness of several angstroms to lower the sheet resistance of the TCO layer such as ITO.

4, an In ₂ O ₃ layer 115 doped with nano dots 125 and a TCO layer 116 are formed on a p-type nitride semiconductor layer 104, as in the above-described embodiment have. On the TCO layer 116, however, at least one metal layer 117 selected from the group consisting of Ag, Pt, Au, Co, Ir having high electrical conductivity and an additional TCO layer 118 formed on the metal layer 117 there's more. This stack of metal layer 117 / additional TCO layer 118 may be stacked one or more times in succession. Preferably, the metal layer 117 may have a thickness of 1 to 10 angstroms to suppress a decrease in light transmittance. This additional metal layer 117 further improves the resistance characteristics of the transparent electrode structure as a whole.

5 is a cross-sectional view of a light emitting device according to another embodiment of the present invention. The light emitting device 300 of FIG. 5 further includes a metal layer 126 of high electrical conductivity formed between the doped In ₂ O ₃ layer 115 and the TCO layer 116, as compared with the light emitting device 200 of FIG. . The metal layer 126 may be at least one selected from the group consisting of Ag, Pt, Au, Co, and Ir. The addition of this metal layer 126 can further improve the resistance characteristics of the transparent electrode structure, thereby further enhancing the current diffusion effect. The metal layer 117 and TCO layer 118 additionally formed in FIG. 5 may be omitted.

6A and 6B are graphs of transmittance and injection current versus forward voltage showing experimental results of the nitride semiconductor light emitting device of Examples and Comparative Examples. In the experiment of FIG. 6A, MIO (Mg-doped In ₂ O ₃ ) layer was formed to a thickness of 30 Å, and ITO / Ag / ITO was formed thereon (MIO / ITO / Ag / ITO) Formation of solid solution nano dots of Mg and Ga between GaN and MIO). In the embodiment of FIG. 6B, a transparent electrode structure having a stacked structure of MIO / Ag / ITO / Ag / ITO was used (formation of solid solution nano dots of Mg and Ga between p-type GaN and MIO). As shown in FIG. 6A, it can be confirmed that the transmittance is excellent in the blue and green wavelength regions, which are the main wavelength ranges of the nitride semiconductor light emitting device. Also, as shown in FIG. 6B, it can be confirmed that the light emitting device of the embodiment exhibits a high current-voltage gradient (low contact resistance) as compared with other comparative examples. Low resistance implies improved ohmic characteristics.

FIGS. 7A and 7B show graphs comparing transmittance and contact resistance characteristics of the transparent electrode structures of Examples and Comparative Examples. FIG. 7A and 7B, a transparent electrode structure (formation of solid solution nano dots of Cu and Ga between p-type GaN and CIO) having a stacked structure of CIO (Cu-doped In ₂ O ₃ ) / ITO and MIO / Transparent electrode structure of ITO (formation of solid solution nano dots of Mg and Ga between p-type GaN and MIO) was used. FIG. 7A is a graph showing the results of the first experiment, and FIG. 7B is a graph showing the results of the second experiment. As shown in the left graph of FIGS. 7A and 7B, the p-side transparent electrode structure of CIO / ITO shows a very high ohmic characteristic. MIO / ITO also showed higher ohmic characteristics than the conventional Pt / ITO structure of the comparative example. As shown in the right graph of FIGS. 7A and 7B, the light emitting device of the embodiment shows excellent light transmittance of 90% or more in the blue and green regions, which are the main wavelength ranges of the nitride semiconductor light emitting device.

The present invention is not limited to the above-described embodiments and the accompanying drawings. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims, .

1 is a cross-sectional view of a conventional nitride semiconductor light emitting device.

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

3 is a diagram schematically illustrating an energy band structure of a main portion including a transparent electrode structure of a nitride semiconductor light emitting device according to an embodiment of the present invention.

4 is a cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention.

5 is a cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention.

6A is a graph showing the transmittance of nitride semiconductor light emitting devices of Examples and Comparative Examples using MIO (Mg-doped In ₂ O ₃ ).

And FIG. 6B is a graph of the injection current-voltage showing the contact resistance characteristics of the nitride semiconductor light emitting device of the embodiment using MIO and the comparative example.

FIG. 7A is a graph of the injection current-voltage graph and the transmittance of the nitride semiconductor light emitting device using CIO (Cu-doped In ₂ O ₃ ) and the first experiment results of the nitride semiconductor light emitting device of the comparative example.

FIG. 7B is a graph of injection current-voltage and transmittance showing the result of the second experiment for the nitride semiconductor light emitting device of the embodiment using the CIO and the comparative example.

Description of the Related Art

100, 200, 300: nitride semiconductor light emitting device 101: substrate

102: n-type nitride semiconductor layer 103: active layer

104: p-type nitride semiconductor layer 107: p-electrode (electrode pad)

108: n- electrode (electrode pad) 115: doped In ₂ O ₃ layer

116: TCO (transparent conductive oxide) layer 120: buffer layer

125: nano dot

Claims (10)

A light emitting structure including an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer sequentially formed on a substrate; And And a transparent electrode structure including an In ₂ O ₃ layer doped with at least one of Mg, Cu, and Zn formed on the p-type nitride semiconductor layer and a transparent conductive oxide layer formed on the doped In ₂ O ₃ layer and, And nano dots of solid solution containing at least one of Mg, Cu, and Zn and Ga are formed at an interface between the p-type nitride semiconductor layer and the doped In ₂ O ₃ layer. The method according to claim 1, Wherein the transparent conductive oxide layer is at least one conductive oxide selected from the group consisting of ITO, ZnO, and MgO. The method according to claim 1, And the nano dots are filled with the doped In ₂ O ₃ layer on the p-type nitride semiconductor layer. The method according to claim 1, Further comprising at least one metal layer formed on the transparent conductive oxide layer and selected from the group consisting of Ag, Pt, Au, Co, and Ir, and an additional transparent conductive oxide layer formed on the metal layer. device. 5. The method of claim 4, Wherein the laminate of the metal layer and the additional transparent conductive oxide layer is continuously laminated one or more times. 5. The method of claim 4, Wherein the metal layer has a thickness of 1 to 10 ANGSTROM. The method according to claim 1, And at least one metal layer formed between the doped In ₂ O ₃ layer and the transparent conductive oxide layer and further including at least one metal layer selected from the group consisting of Ag, Pt, Au, Co and Ir. The method according to claim 1, Wherein the doped In ₂ O ₃ layer has a thickness of 10 to 200 ANGSTROM. The method according to claim 1, Wherein the transparent conductive oxide layer has a thickness of 1000 to 6000 ANGSTROM. The method according to claim 1, The nano dots may be formed by a chemical reaction between Ga in the p-type nitride semiconductor layer and Mg, Cu or Zn in the doped In ₂ O ₃ layer by heat treatment on the doped In ₂ O ₃ layer and the transparent conductive oxide layer Wherein the nitride semiconductor light emitting device is formed of a nitride semiconductor.

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