KR20120102468A - Light emitting device - Google Patents

Abstract

PURPOSE: A light emitting device is provided to improve luminous efficiency by reducing current crowding. CONSTITUTION: A photoelectric layer(120) is formed on a substrate(110) and includes a first semiconductor layer(122), an active layer(123), and a second semiconductor layer(124). An ohmic contact layer(130) is formed on the second semiconductor layer. At least one first electrode(140) is formed on a part of the first semiconductor layer. At least one second electrode(150) is formed on the ohmic contact layer.

Description

Light Emitting Device {LIGHT EMITTING DEVICE}

The present invention relates to a light emitting device, and more particularly, to a light emitting device including a photoelectric layer made of nitride semiconductor.

A light emitting device (LED) is a kind of photoelectric device including a photoelectric layer composed of a plurality of p-n bonded semiconductor layers, and converts electrical energy into optical energy to emit light.

Such a light emitting device has an advantage of having high energy efficiency since it can emit light of high brightness at low voltage, compared to other devices that emit light. In particular, the light emitting device in which the photoelectric layer is formed of a gallium nitride (GaN) -based nitride semiconductor can emit light in a wide range of wavelengths including infrared rays to infrared rays. Accordingly, the light emitting device may be variously applied to various automation devices such as a backlight unit, a display board, a display, and a home appliance of a liquid crystal display, and may be used for environmentally harmful substances such as arsenic (As) and mercury (Hg). Since it does not include, it has been spotlighted as a next-generation light source.

In general, a light emitting device includes a photoelectric layer including a plurality of semiconductor layers including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, a first electrode for injecting electrons into the n-type semiconductor layer, and a first electrode. And a first electrode pad connecting between the outside and the outside, a second electrode injecting holes into the p-type semiconductor layer, and a second electrode pad connecting between the second electrode and the outside.

When the forward voltage is applied between the first electrode and the second electrode, the light emitting device configured as described above encounters holes and electrons injected through the first and second electrodes in the photoelectric layer to recombine to generate excitons. At this time, the excitons emit extra energy as light from the excited state to the ground state.

However, holes and electrons tend to move in the path of the least resistance, so that a current is concentrated in the shortest distance region between the first electrode and the second electrode (hereinafter referred to as "current density phenomenon"). . In particular, the resistance of each of the first electrode and the second electrode gradually increases in proportion to the increased length as it moves away from the first electrode pad and the second electrode pad. Accordingly, a large amount of electrons and holes are diffused and concentrated in an area adjacent to the first electrode pad and the second electrode pad in the photoelectric layer, and the first electrode pad and the second electrode pad are spaced apart from the first electrode pad and the second electrode pad. A very small amount of electrons and holes are diffused than the region adjacent to the second electrode pad. That is, the current density phenomenon is intensified by the resistance of each of the first electrode and the second electrode.

Due to this current condensation, charges (herein, "charges" collectively refer to positive and negative charges carried by holes and electrons, respectively) do not diffuse widely in the photoelectric layer, but accumulate in only a portion of the region, thereby accumulating electrons and holes in the active layer. Since the possibility of recombination of the is lowered, there is a problem that the rate (hereinafter referred to as "luminescence efficiency") that the charge injected from the outside is converted to light is low.

As such, charges accumulated in some regions are converted into thermal energy to generate high-temperature heat in the device, and thus, there is a problem in that the deterioration of the device life and reliability decrease due to deterioration.

The present invention is to provide a light emitting device that can improve the luminous efficiency by lowering the current density.

In order to solve such a problem, the present invention is a substrate; A photovoltaic layer including a first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on the substrate; An ohmic contact layer formed of a transparent conductive material on the second semiconductor layer; A first electrode pad formed on a portion of the first semiconductor layer exposed by removing portions of the ohmic contact layer, the second semiconductor layer, and the active layer; At least one first electrode formed on the partial region of the first semiconductor layer and extending from the first electrode pad, and having a cross-sectional area that gradually increases as the length of the first electrode pad extends; A second electrode pad formed on the ohmic contact layer; And at least one second extending from the second electrode pad so as to alternate with the plurality of first electrodes on the ohmic contact layer, and having a cross-sectional area gradually increasing as the length extending from the second electrode pad increases. Provided is a light emitting device comprising an electrode.

The light emitting device according to the present invention extends from the second electrode pad so as to alternate with at least one first electrode on the at least one first electrode and the second semiconductor layer which are formed from the first electrode pad on the first semiconductor layer. And at least one second electrode. In this case, each of the at least one first electrode has a cross-sectional area that gradually increases as the length extending from the first electrode pad increases, and each of the at least one second electrode has a cross-sectional area that gradually increases as the length extending from the second electrode pad increases. Have That is, each of the at least one first and second electrodes is formed to have a cross-sectional area that extends along the length of the first and second electrode pads. As such, each of the at least one first and second electrodes has a length and an increasing cross-sectional area that are increased in proportion to the distance between the first and second electrode pads, and thus, the distance between the first and second electrode pads. Since the increase in the resistance according to the increase can be minimized, it is possible to minimize the degradation of the charge transfer due to the increase in the resistance of the first and second electrodes.

In addition, the light emitting device according to the present invention further includes a plurality of diffusion holes formed through each of the at least one first and second electrodes, wherein the plurality of light emitting elements are arranged along each of the at least one first and second electrodes. The diffusion holes of have a separation distance that decreases away from the first and second electrode pads. Through the plurality of diffusion holes, diffusion of holes and electrons from at least one first and second electrodes toward the photoelectric layer may be promoted.

As described above, the light emitting device according to the present invention has a cross-sectional area that gradually increases as the distance from the first and second electrode pads increases, so that at least one of the first and second electrodes capable of minimizing the increase in resistance according to the length, and at least The current density may be lowered by including a plurality of diffusion holes formed to penetrate each of the first and second electrodes to promote charge transfer from the first and second electrodes to the photoelectric layer. Therefore, the charge can be diffused in the photoelectric layer more widely than the conventional one, so that the luminous efficiency of the device can be improved, and the lifespan of the device caused by deterioration due to high current density can be prevented and reliability can be prevented.

1 is a plan view showing a light emitting device according to an embodiment of the present invention.
2 is a cross-sectional view taken along line AA ′ of FIG. 1 according to a first embodiment of the present invention.
3 is a cross-sectional view taken along line BB ′ of FIG. 1 according to a first embodiment of the present invention.
4A and 4B illustrate the diffusion of electrons and holes in the light emitting device according to the first embodiment of the present invention.
5 shows various cross-sectional views of the diffusion hole according to the first embodiment of the present invention.
6 is a cross-sectional view taken along line BB ′ of FIG. 1 according to a second exemplary embodiment of the present invention.
7 is a cross-sectional view taken along line BB ′ of FIG. 1 according to a third exemplary embodiment of the present invention.

Hereinafter, light emitting devices according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the light emitting device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

1 is a plan view showing a light emitting device according to an embodiment of the present invention. 2 is a cross-sectional view illustrating the AA ′ of FIG. 1 according to the first embodiment of the present invention, and FIG. 3 is a cross-sectional view illustrating the B-B ′ of FIG. 1 according to the first embodiment of the present invention. 4A and 4B illustrate the diffusion of electrons and holes in the light emitting device according to the first embodiment of the present invention. 5 shows various cross-sectional views of the diffusion holes according to the first embodiment of the present invention.

First, the cross section of the light emitting device according to the first embodiment of the present invention will be described.

2 and 3, the light emitting device according to the first embodiment of the present invention includes a substrate 110, a buffer layer 121 and a first semiconductor layer 122 sequentially stacked on the substrate 110. , The photoelectric layer 120 including the active layer 123 and the second semiconductor layer 124, the ohmic contact layer 130 formed of a transparent conductive material on the second semiconductor layer, the ohmic contact layer 130, and the second The at least one first electrode 140 and the ohmic contact layer 130 formed on a portion of the first semiconductor layer 122 exposed by removing a portion of each of the semiconductor layer 124 and the active layer 123. Formed through at least one second electrode 150 and at least one first electrode 140 formed through the plurality of first diffusion holes 141 and at least one second electrode 150. It includes a plurality of second diffusion holes 151.

As shown in FIG. 1, the light emitting device according to the first embodiment of the present invention may include a first electrode pad 142 and an ohmic contact layer formed on a portion of the exposed first semiconductor layer 122. The second electrode pad 152 is formed on the 130.

The substrate 110 may be selected from Al ₂ O ₃ (Sapphire: Sapphire), SiC, and AlN having a crystal structure similar to GaN, GaN-based, and GaN. In particular, the substrate 110 may be selected as a sapphire (Al ₂ O ₃ ) substrate having the advantages of low cost, low strain due to alkali or acid, and low strain due to heat.

The buffer layer 121 is a buffer layer for reducing crystal defects generated in the photoelectric layer 120 due to a lattice constant difference and a thermal expansion coefficient difference between the substrate 110 and the semiconductor material forming the photoelectric layer 120. The buffer layer 121 may be formed of an undoped nitride semiconductor or an n-type nitride semiconductor grown in an atmosphere including low temperature heat that grows the semiconductor material horizontally on the growth surface.

The first semiconductor layer 122 is formed on the buffer layer 121 as an n-type nitride semiconductor that is doped with n-type impurities to increase electron mobility. In this case, the n-type impurity may be Si.

The active layer 123 is formed on the first semiconductor layer 122 as a nitride semiconductor having a quantum well structure. The active layer 123 generates light using energy generated by exciton generated by recombination of electrons and holes injected through the first electrode 140 and the second electrode 150 to a standby state. .

For example, when the semiconductor material forming the photoelectric layer 120 is gallium nitride (GaN) -based, the active layer 123 may include a barrier layer of In _x (Al _y Ga _(1-y) ) N and In _x (Al _y). It may be formed as a single quantum well structure or multiple quantum well structure (MQW) consisting of a well layer of Ga _(1-y) ) N. In this case, according to the composition ratio of the nitride semiconductors (InGaN, GaN) of the barrier layer and the well layer, the wavelength region of the light emitted from the light emitting device is freely determined from the long wavelength to the short wavelength having the AlN (˜6.4 eV) band gap.

The second semiconductor layer 124 is formed on the active layer 123 as a p-type nitride semiconductor that is doped with p-type impurities to increase hole mobility. In this case, the p-type impurity may be Mg.

Meanwhile, the plurality of semiconductor layers 121 ˜ 124 constituting the photoelectric layer 120 may be formed by growing a semiconductor material using a metal organic chemical vapor deposition (MOCVD) method.

The ohmic contact layer 130 is for diffusing holes injected into the second electrode 150 to the second semiconductor layer 124 as wide as possible. The ohmic contact layer 130 is formed of a transparent conductive material on the second semiconductor layer 124. At this time, the transparent conductive material forming the ohmic contact layer 130 is any one of the metal oxide of SnO ₂ , ZnO, In ₂ O ₃ and TiO ₂ and these metal oxides of F, Sn, Al, Fe, Ga and Nb At least one may be selected as the doped material.

The at least one first electrode 140 and the first electrode pad 142 may be exposed by removing partial regions of the ohmic contact layer 130, the second semiconductor layer 124, and the active layer 123, respectively. It is formed on some regions of the 122. In this case, each of the at least one first electrode 140 has a shape extending from the first electrode pad 142 like a branch. In particular, as shown in FIG. 1, according to the first embodiment of the present invention, each of the at least one first electrode 140 gradually increases in cross-sectional area as the length extending from the first electrode pad 142 increases. Has

At least one second electrode 150 and the second electrode pad 152 are formed on the ohmic contact layer 130. In this case, each of the at least one second electrode 150 alternates with the at least one first electrode 140 on a light emitting surface (wherein the “light emitting surface” means an upper surface of which light is mainly emitted from the light emitting device). The second electrode pad 152 has a shape extending from a branch. In particular, as shown in FIG. 1, according to the first embodiment of the present invention, each of the at least one second electrode 150 has a cross-sectional area that gradually increases as the length extending from the second electrode pad 152 increases. Has

Meanwhile, the at least one first electrode 140, the first electrode pad 142, the at least one second electrode 150, and the second electrode pad 152 may be formed of the same or different conductive materials. Ni, Au, Pt, Ti, Al, and any one metal of Cr or may be formed of an alloy containing two or more.

The plurality of first diffusion holes 141 are formed to pass through the first electrode 140 and are arranged side by side along each of the at least one first electrode 140. At this time, in the plurality of first diffusion holes 141 arranged in each of the first electrodes 140, the distance between two adjacent first diffusion holes 141 is farther from the first electrode pad 142. Gradually decreases.

The plurality of second diffusion holes 151 are formed to penetrate the second electrode 150, and are arranged side by side along each of the at least one second electrode 150. At this time, in the plurality of second diffusion holes 151 arranged in each second electrode 150, the distance between two adjacent second diffusion holes 151 is farther away from the second electrode pad 152. Gradually decreases.

Alternatively, the plurality of first and second diffusion holes 141 and 151 arranged in each of the at least one first and second electrodes 140 and 150 may be separated from the first and second electrode pads 142 and 152. Increasingly, it may be formed in an increasing number while being spaced apart at regular intervals or gradually narrowing intervals, or may be formed in an increasingly large cross-sectional area.

As described above, according to the first embodiment of the present invention, each of the at least one first electrode 140 and the at least one second electrode 150 is a first electrode pad 142 and the second electrode pad 152. As it extends from, it has a cross-sectional area that becomes wider as it becomes longer.

As shown in Equation 1 below, the resistance R is proportional to the length L and inversely proportional to the cross-sectional area A. In consideration of this, each of the at least one first electrode 140 and the at least one second electrode 150 each having a cross-sectional area gradually increasing in accordance with the elongated extension length is the first electrode pad 142 and the second electrode pad. It can be expected to have a resistance that does not increase significantly by the length extending from 152.

Therefore, as shown by the arrow in FIG. 4A, the charge is close to the first electrode pad 142 and the second electrode pad 152 even in a region far from the first electrode pad 142 and the second electrode pad 152. Since it can be moved similarly to, the current density due to the resistance of the electrodes (140, 150) can be alleviated.

In addition, the light emitting device according to the embodiment of the present invention may include a plurality of first and second diffusion holes 141 formed to penetrate each of the at least one first electrode 140 and the at least one second electrode 150. 151). Electrons and holes moving through at least one first electrode 140 and at least one second electrode 150 through the plurality of first and second diffusion holes 141 and 151 are transferred to the photoelectric layer 120. It can spread more easily. In particular, the separation distance between the plurality of diffusion holes 141 and 151 arranged side by side along the electrodes 140 and 150 becomes smaller as the distance from the electrode pads 142 and 152 increases.

Thus, as shown in FIG. 4B, the diffusion of charges through the plurality of first and second diffusion holes 141 and 151 may be further facilitated, and current condensation may be alleviated.

Meanwhile, in FIG. 1, the plurality of first and second diffusion holes 141 and 151 have a circular cross section, but the first embodiment of the present invention is not limited thereto.

That is, as illustrated in FIG. 5A, the plurality of first and second diffusion holes 141 and 151 may have an elliptical cross section, or as illustrated in FIGS. 5B and 5C. As one may have a circular or elliptical cross section with an uneven edge. As described above, when the cross-sections of the diffusion holes 141 and 151 have an uneven outline, the contact area between the diffusion holes 141 and 151 and the electrodes 140 and 150 becomes wider, so that the movement path of electric charges becomes wider. It can be made easier to spread the current.

Next, the light emitting devices according to the second and third embodiments of the present invention will be described.

As shown in FIG. 6, the light emitting device according to the second embodiment of the present invention further includes a plurality of second diffusion holes 153 formed through the second electrode 150 and the ohmic contact layer 130. Except for that, since it is the same as the first embodiment shown in Figs. 1 to 3, descriptions overlapping below will be omitted.

As shown in FIG. 7, except that the light emitting device according to the third embodiment of the present invention includes a plurality of first and second diffusion holes 143 and 154 filled with a metal material, 1 and 3 and the second embodiment shown in FIG. 6, the description thereof will be omitted. In this case, the metal material filling the inside of the plurality of first and second diffusion holes 143 and 154 may be selected to be the same as the first and second electrodes 140 and 150, or may be different from each other having higher conductivity. It may be chosen.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes may be made without departing from the technical spirit of the present invention.

110: substrate 120: photoelectric layer
121: buffer layer 122: first semiconductor layer
123: light emitting layer 124: second semiconductor layer
130: ohmic contact layer 140: first electrode
142: first electrode pad 150: second electrode
152: second electrode pads 141, 151, 153, 154: diffusion holes

Claims (7)

Board;
A photovoltaic layer including a first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on the substrate;
An ohmic contact layer formed of a transparent conductive material on the second semiconductor layer;
A first electrode pad formed on a portion of the first semiconductor layer exposed by removing portions of the ohmic contact layer, the second semiconductor layer, and the active layer;
At least one first electrode formed on the partial region of the first semiconductor layer and extending from the first electrode pad, and having a cross-sectional area that gradually increases as the length of the first electrode pad extends from the first electrode pad;
A second electrode pad formed on the ohmic contact layer; And
At least one second electrode extending from the second electrode pad so as to alternate with the plurality of first electrodes on the ohmic contact layer, and having a cross-sectional area gradually increasing as the length extending from the second electrode pad increases Light emitting device comprising a. The method of claim 1,
And a plurality of diffusion holes formed through the at least one first electrode and the at least one second electrode, respectively. The method of claim 2,
The light emitting device of claim 1, wherein a distance between the plurality of diffusion holes formed through one of the at least one first electrode decreases as the distance from the first electrode pad increases. The method of claim 2,
The light emitting device of claim 1, wherein a distance between the plurality of diffusion holes formed through one of the at least one second electrode decreases as the distance from the second electrode pad increases. The method of claim 2,
The plurality of diffusion holes formed through any one of the at least one second electrode is further formed through the ohmic contact layer. 6. The method according to claim 2 or 5,
The plurality of diffusion holes include an interior filled with a metal material. The method of claim 2,
A cross section of each of the plurality of diffusion holes is a circular or elliptical cross-section, or a circular or elliptical shape having an uneven edge.

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