KR20060112064A - Light emitting device - Google Patents

Abstract

A light emitting device is provided to reduce an operation voltage of a device by making a smooth flow of current from a transparent conductive oxide layer to a P-GaN layer. A light emitting structure(100) is composed of a plurality of material layers between which an active layer(101) is interposed to emit light by injected current. A current transport enhanced layer(102) has a work function smaller than that of a material constituting the upper surface of the light emitting structure to improve the mobility of carriers for current injection, including a material of the material layer constituting the upper surface of the light emitting structure. A transparent conductive oxide layer(103) is formed on the current transport enhanced layer, having a work function greater than that of the current transport enhanced layer. A plurality of grooves(103a) are periodically arranged on the upper surface of the transparent conductive oxide layer. An N-GaN layer, an active layer and a P-GaN layer are sequentially stacked on a substrate in the light emitting structure. The light emitting structure from the P-GaN layer to a part of the N-GaN layer is mesa-etched.

Description

Light emitting device

1 is a cross-sectional view of a light emitting diode according to the prior art.

2 is a cross-sectional view of another light emitting diode according to the prior art.

3 is a cross-sectional view of a light emitting device according to the present invention;

4A to 4C are plan views illustrating grooves formed in the transparent conductive oxide film of the light emitting device according to the present invention.

5 is a cross-sectional view illustrating an embodiment of a light emitting device according to the present invention.

6A and 6B are energy band diagrams of a transparent conductive oxide film, a current transfer enhancement layer, and P-GaN before and after heat treatment according to the present invention.

7 is a photograph photographing a state in which a groove is formed in the transparent conductive oxide film of the light emitting device according to the present invention;

<Description of the symbols for the main parts of the drawings>

100 light emitting structure 101 active layer

102,240: current transfer enhancement layer 103,250,300: transparent conductive oxide film

103a, 103b, 250a, 301: groove 200: substrate

210: N-GaN layer 220: active layer

230: P-GaN layer 260: P-electrode

270: N-electrode

The present invention relates to a light emitting device, and more particularly, to a current transport enhancement layer having a work function smaller than the work function of a material forming the upper surface of the light emitting structure, and a work function larger than the current transport enhancement layer. And a transparent conductive oxide film (TCO) in which a plurality of grooves including grooves periodically arranged on the upper surface are formed to facilitate a current flow from the transparent conductive oxide film to the P-GaN layer. The present invention relates to a light emitting device capable of lowering an operating voltage and improving light output.

In general, group III-V compound semiconductor elements are made of light emitting elements such as light emitting diode elements and laser diode elements, light receiving elements such as solar cells and optical sensors, or nitride semiconductors used in electronic devices such as transistors and power devices. A -V compound semiconductor device.

The group III-V compound semiconductor has a direct transition type, which has high luminous efficiency, and can be used as a light emitting wavelength from red to purple and ultraviolet region by adjusting In concentration, and is particularly useful for short wavelength light emitting devices.

Such a light emitting device is an n-type gallium nitride-based Group III-V compound semiconductor layer and a p-type gallium nitride-based Group III-V compound semiconductor layer doped with p-type impurities on a substrate by a MOVPE growth method, p-type and n-type semiconductors It has a narrow width in between, and has a structure in which an active layer having a band gap smaller than that of p-type and n-type semiconductors is stacked.

Since the stacked light emitting devices are generally grown on sapphire substrates having low-cost insulation, they cannot have so-called top-down electrodes used in the fabrication of existing GaAs and InP devices.

Due to such structural constraints, gallium nitride-based group III-V compound semiconductor light emitting devices, which are currently widely manufactured, have a structure as shown in FIG. 1.

In the case of using a conductive substrate, a device having a top-down electrode structure as shown in FIG. 2 can be manufactured.

1 is a cross-sectional view of a light emitting diode according to the prior art, in which an N-type semiconductor layer 11, an active layer 12, and a P-type semiconductor layer 13 are sequentially stacked on a substrate 10; Mesa is etched from the P-type semiconductor layer 13 to a part of the N-type semiconductor layer 11; A transparent electrode 14 is formed on the P-type semiconductor layer 13; A P electrode 15 is formed on the transparent electrode 14; An N electrode 16 is formed on the mesa-etched N-type semiconductor layer 11.

As such, when the configured light emitting diode flows from the N-type semiconductor layer 11 to the P-type semiconductor layer 13, light is emitted from the active layer 12.

FIG. 2 is a cross-sectional view of another light emitting diode according to the related art, in which an N-GaN layer 21, an active layer 22, and a P-GaN layer 23 are sequentially stacked on a conductive substrate 20. )Wow; A transparent conductive oxide film (TCO) 25 formed on the P-GaN layer 23 of the laminated structure 24; A P-electrode 26 formed on the transparent conductive oxide film 25; And an N-electrode 27 formed under the conductive substrate 20.

In the above-described conventional light emitting diode structure, a transparent electrode is formed on the p-GaN, and the transparent electrode is formed by sequentially depositing two or more metals such as Ni, Au, Pd, Pt, Ru, Ir, or TCO. It is also formed by depositing ITO, IZO, ZnO, AZO, etc. of the transparent conducting oxide.

The purpose of the transparent electrode is to reduce the operating voltage of the device by facilitating current diffusion and to increase the external quantum efficiency so that the light emitted to the outside can be maximized by increasing the light transmittance.

However, currently used Ni / Au series transparent electrodes lower the ohmic resistance of p-GaN to facilitate current spreading, thereby reducing the operating voltage of the device. The result is a decrease in the light transmittance, which reduces external quantum efficiency.

In addition, the TCO (Transparent Conduction Oxide) -based transparent electrode shows a high light transmittance of 90% or more, but since the work function of the electrode is 5 eV or less, it is difficult to obtain a low operating voltage by making an ohmic contact directly to p-GaN. .

In order to overcome this problem, the P-GaN layer should be doped at a high concentration of 5 x 10 ¹⁸ cm ^-3 or more, which causes a problem of performing a difficult process such as high implant or diffusion with dopants such as Mg and Zn. .

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a current transport enhancement layer and a current transport enhancement layer having a work function smaller than that of the material forming the upper surface of the light emitting structure. A transparent conductive oxide film (TCO) having a larger work function and having a plurality of grooves including grooves periodically arranged on the upper surface is formed to smoothly flow current from the transparent conductive oxide film to the P-GaN layer. It is an object of the present invention to provide a light emitting device capable of reducing the operating voltage of the device and improving the light output.

According to a preferred aspect of the present invention, there is provided a light emitting structure including a plurality of material films interposed with an active layer that emits light by an injected current;

A current transfer enhancement layer including a material of a material film forming an upper surface of the light emitting structure and having a work function smaller than a work function of a material forming the upper surface of the light emitting structure so as to improve movement of a carrier for current injection; Current Transport Enhanced Layer);

A transparent conductive oxide film (TCO) is formed on the current transfer enhancement layer and has a larger work function than the current transfer enhancement layer and includes a plurality of grooves including grooves periodically arranged on an upper surface thereof. Provided is a light emitting device configured to include.

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

3 is a cross-sectional view of a light emitting device according to the present invention, comprising: a light emitting structure 100 made of a plurality of material films having an active layer 101 emitting light by injected current; It includes a material of the material film forming the upper surface of the light emitting structure 100, a work function smaller than the work function of the material forming the upper surface of the light emitting structure 100 to improve the movement of the carrier for the current injection A current transport enhanced layer (CTEL) 102 having; A transparent conductive oxide layer formed on the current transfer enhancement layer 102 and having a larger work function than the current transfer enhancement layer and having a plurality of grooves 103a including grooves periodically arranged on an upper surface thereof. Conduction Oxide, TCO) (103).

As such, when a plurality of grooves including grooves periodically arranged on the upper surface of the transparent conductive oxide film 103 are formed, the periodically arranged grooves may emit light having a specific wavelength to the outside almost without loss. Forming a photonic crytal, the grooves other than the periodically arranged grooves can prevent total reflection of the light, thereby improving the light output emitted from the active layer.

4A to 4C are plan views illustrating grooves formed in the transparent conductive oxide film of the light emitting device according to the present invention. First, as shown in FIG. 4A, grooves periodically arranged among the grooves formed on the transparent conductive oxide film top surface of the light emitting device ( 103a are grooves arranged at regular intervals d1, and the other grooves 103b are grooves distributed irregularly.

In the present invention, as shown in Fig. 4a, the grooves 103a that are periodically arranged are formed larger than the other grooves 103b, and are formed in the same manner as in Fig. 4b.

As shown in FIG. 4A, the number of the grooves 103a periodically arranged is larger than that of the other grooves 103b or less than that shown in FIG. 4C.

5 is a cross-sectional view for describing an embodiment of the light emitting device according to the present invention, in which an N-GaN layer 210, an active layer 220, and a P-GaN layer 230 are sequentially stacked on the substrate 200. It is done; Mesa is etched from the P-GaN layer 230 to a part of the N-GaN layer 210; A current transport enhancement layer 240 including GaN on the P-GaN layer 230 to improve carrier movement to facilitate current flow; A transparent conductive oxide film (TCO) 250 is formed on the current transfer enhancement layer 240 and includes a plurality of grooves including grooves periodically arranged on an upper surface thereof; A P-electrode 260 is formed on the transparent conductive oxide film 250; An N-electrode 270 is formed on the mesa-etched N-GaN layer 210.

Here, the N-GaN layer 210, the active layer 220 and the P-GaN layer 230 are sequentially stacked on the substrate 200; The structure in which Mesa is etched from the P-GaN layer 230 to a part of the N-GaN layer 210 is an example of the light emitting structure of FIG. 3.

Meanwhile, an energy band diagram of the P-GaN layer 230 / current transfer enhancement layer 240 / transparent conductive oxide film 250 will be described with reference to FIGS. 6A and 6B.

That is, the energy band diagram in the structure in which the current transfer enhancement layer 240 and the transparent conductive oxide film 250 are sequentially stacked on the P-GaN layer 230 is in FIG. 6A.

Therefore, as shown in FIG. 6A, the transparent conductive oxide film 250 in the deposited state is not in ohmic contact with the current transfer enhancement layer.

However, if the transparent conductive oxide film is deposited on the current transfer enhancement layer, and then the heat treatment process is performed to increase the work function of the transparent conductive oxide film to 4.7 to 5.3 eV, as shown in FIG. It can be moved, and ohmic contact is made.

The current transfer enhancement layer 240 may be formed of any one of P ⁺ GaN layer, InGaN layer, AlGaN layer, and InAlGaN layer or a combination thereof.

In addition, the thickness of the current transfer enhancement layer 240 is preferably 1 ~ 50nm, the carrier should be well over the potential barrier or tunneling only if the current transfer enhancement layer 240 is formed in this thickness range The current flows smoothly.

In addition, the transparent conductive oxide film 250 is preferably any one of ITO, IZO, ZnO and AZO.

7 is a photograph showing a state in which a groove is formed in the transparent conductive oxide film of the light emitting device according to the present invention, in which the groove 301 is formed in the transparent conductive oxide film 300, and the groove 301 is formed. Is performed by a photolithography process or an E-beam lithography process.

As described above, the present invention has a current transport enhancement layer having a work function smaller than the work function of the material forming the upper surface of the light emitting structure, and has a work function larger than that of the current transport enhancement layer. A transparent conductive oxide film (TCO) is formed in which a plurality of grooves including periodically arranged grooves are formed to smoothly flow current from the transparent conductive oxide film to the P-GaN layer, thereby lowering the operating voltage of the device. It is possible to improve the light output.

Although the invention has been described in detail only with respect to specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (7)

 A light emitting structure including a plurality of material films having an active layer emitting light by the injected current; A current transfer enhancement layer including a material of a material film forming an upper surface of the light emitting structure and having a work function smaller than a work function of a material forming the upper surface of the light emitting structure so as to improve movement of a carrier for current injection; Current Transport Enhanced Layer); A transparent conductive oxide film (TCO) is formed on the current transfer enhancement layer and has a larger work function than the current transfer enhancement layer and includes a plurality of grooves including grooves periodically arranged on an upper surface thereof. Light emitting device configured to include. The method of claim 1, The light emitting structure, An N-GaN layer, an active layer and a P-GaN layer are sequentially stacked on the substrate; Light emitting device, characterized in that the structure is mesa (Mesa) etching from the P-GaN layer to a portion of the N-GaN layer. The method of claim 2, The current transfer enhancement layer, A light emitting diode characterized in that the film is any one or a combination of a P ⁺ GaN layer, an InGaN layer, an AlGaN layer, and an InAlGaN layer. The method of claim 1, The work function of the transparent conductive oxide film is 4.7 to 5.3eV, characterized in that the light emitting device. The method of claim 1, The periodically arranged grooves, A light emitting device, characterized in that formed larger than the other grooves. The method of claim 1, The periodically arranged grooves, The light emitting device, characterized in that formed larger than the other grooves. The method of claim 1, The thickness of the current transfer enhancement layer is a light emitting device, characterized in that 1 to 50nm.

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