KR100716647B1 - Light emitting diode with an energy barrier layer for current spreading - Google Patents

Abstract

A light emitting diode having an energy barrier layer for current distribution is disclosed. The light emitting diode includes a gallium nitride series first n-type semiconductor layer and a gallium nitride series first p-type semiconductor layer. An active layer is interposed between the first n-type semiconductor layer and the first p-type semiconductor layer, and a gallium nitride series second n-type semiconductor layer is interposed between the first n-type semiconductor layer and the active layer. The n-type energy barrier layer is interposed between the first n-type semiconductor layer and the second n-type semiconductor layer. The n-type energy barrier layer is formed of a gallium nitride series having a larger energy band gap than the first n-type semiconductor layer. Thus, the n-type energy barrier layer acts as an energy barrier for electrons entering the active layer from the first n-type semiconductor layer, and the electrons are evenly dispersed in the first n-type semiconductor layer.

Light Emitting Diodes, Energy Barrier Layers, Current Spreading

Description

LIGHT EMITTING DIODE WITH AN ENERGY BARRIER LAYER FOR CURRENT SPREADING}

1 is a cross-sectional view illustrating a light emitting diode having a well layer for current distribution according to the prior art.

Figure 2 is an energy band diagram for explaining the current distribution according to the prior art.

3 is a cross-sectional view illustrating a light emitting diode having an energy barrier layer for current distribution according to embodiments of the present invention.

4 is an energy band diagram for describing current dispersion according to an embodiment of the present invention.

5 is an energy band diagram for describing current distribution according to another embodiment of the present invention.

The present invention relates to a light emitting diode, and more particularly to a light emitting diode having an energy barrier layer for current distribution.

Gallium nitride (GaN) series light emitting diodes (LEDs) have been in use for more than a decade and have significantly changed LED technology. GaN series LEDs are currently used in a variety of applications, including color LED displays, LED traffic signals, and white LEDs.

Recently, high-efficiency white LEDs are expected to replace fluorescent lamps. In particular, the efficiency of white LEDs has reached a level similar to that of conventional fluorescent lamps. However, there is a possibility that the LED efficiency is further improved, and thus continuous efficiency improvement is further required.

Two major approaches are being attempted to improve LED efficiency. The first is to increase the internal quantum efficiency determined by the crystal quality and the epilayer structure, and the second is to increase the light extraction efficiency.

Improving the light extraction efficiency has been a major challenge to eliminate the internal light loss by adopting a heat dissipation structure, a rough surface and a patterned sapphire substrate and the like.

The roughened surface prevents light incident on the surface from returning to the inside of the LED by total reflection, thereby emitting light to the outside. In addition, the patterned sapphire substrate can improve the light extraction efficiency by reducing the total reflection of light is lost between the LED and the substrate.

On the other hand, LEDs with improved epitaxial structure to improve internal quantum efficiency are "enhanced output power in an InGaN-GaN multiquantum- in InGaN-GaN multi-quantum well light emitting diode with InGaN current spreading layer". It was disclosed in IEEE Photonics Technology Letters (Vol. 13, No. 11) published in November 2001 by Sheu et al. under the title well light-emitting diode with an InGaN currernt-spreading layer. 1 illustrates an LED disclosed by Schew et al.

Referring to FIG. 1, a low-temperature GaN nucleation layer 13, an n-type GaN layer 15, an n-type InGaN current spreading layer 17, an n-type GaN layer 19, and an active layer are formed on a sapphire substrate 11. (21), the p-type AlGaN layer 23 and the p-type GaN layer 25 are stacked in this order. The n-type semiconductor layers are formed by doping Si, and the p-type semiconductor layers are formed by doping Mg. The active layer 21 has a multi-quantum well structure in which an InGaN layer and a GaN layer are periodically formed.

FIG. 2 shows an energy band diagram based on the current spreading layer 17 in the epilayer structure of FIG. 1.

Referring to FIG. 2, the InGaN current spreading layer 17 forms a well between the GaN layers 15 and 19 because the energy band gap is smaller than that of the GaN layers 15 and 19. Electrons traveling from the n-type GaN layer 15 toward the active layer 21 are accumulated in the InGaN current distribution layer 17 by an energy barrier at the interface between the InGaN current distribution layer 17 and the GaN layer 19. Therefore, the electrons are evenly distributed in the InGaN current spreading layer 17 and then flow toward the active layer 21.

As a result, since the electrons and holes in the active layer 21 are combined in the entire area of the active layer 21, current crowding can be prevented, thereby improving the internal quantum efficiency, thereby improving the light output.

However, the optimum growth temperature of the InGaN current spreading layer 17 is considerably lower than the growth temperatures of the GaN layers 15 and 19. Therefore, after growing the GaN layer 15, the growth temperature must be lowered to grow the InGaN layer 17, which leads to an increase in processing time, thereby reducing the light emitting diode throughput.

Meanwhile, an undoped GaN layer or a lightly doped n-GaN layer may be interposed between the n-type GaN layers 15 and 19 instead of the InGaN current spreading layer 17, but the undoped GaN layer or the n-GaN layer High resistance increases the forward voltage.

The technical problem to be achieved by the present invention is to provide a light emitting diode that can evenly disperse electrons without significantly changing the growth temperature.

The technical problem to be achieved by the present invention is to provide a light emitting diode that can evenly distribute electrons while preventing an increase in series resistance.

In order to achieve the above technical problem, the present invention provides a light emitting diode having an energy barrier layer for current dispersion. A light emitting diode according to embodiments of the present invention includes a gallium nitride based first n-type semiconductor layer and a gallium nitride based first p-type semiconductor layer. An active layer is interposed between the first n-type semiconductor layer and the first p-type semiconductor layer, and a gallium nitride based second n-type semiconductor layer is interposed between the first n-type semiconductor layer and the active layer. An n-type energy barrier layer is interposed between the first n-type semiconductor layer and the second n-type semiconductor layer. The n-type energy barrier layer is formed of a gallium nitride series having an energy band gap larger than that of the first n-type semiconductor layer. Since the n-type energy barrier layer acts as an energy barrier for electrons injected from the first n-type semiconductor layer to the active layer, electrons are dispersed in the first n-type semiconductor layer. Therefore, electrons can be injected evenly toward the active layer, thereby improving luminous efficiency. In addition, the doping concentration of the energy barrier layer can be made high, thereby increasing the series resistance. Here, the gallium nitride-based semiconductor layers mean a two-component, three-component or four-component nitride semiconductor layer represented by (B, Al, Ga, In) N.

In order to prevent the formation of an energy barrier at the interface between the n-type energy barrier layer and the second n-type semiconductor layer, the second n-type semiconductor layer preferably has an energy band gap smaller than that of the n-type energy barrier layer. . The first n-type semiconductor layer and the second n-type semiconductor layer may be GaN, and the energy barrier layer may be AlGaN. AlGaN can be grown at a growth temperature that is substantially the same as the growth temperature of GaN, and by controlling the content of Al less, it is possible to prevent the crystalline of the active layer from deteriorating.

Meanwhile, a highly doped gallium nitride based n-type current spreading layer may be interposed between the first n-type semiconductor layer and the n-type energy barrier layer. The energy band gap of the n-type current spreading layer may be smaller than or equal to the energy band gap of the first n-type semiconductor layer. The n-type current spreading layer is adjacent to the n-type energy barrier layer, allowing electrons to be more evenly dispersed within the n-type current spreading layer.

In addition, the first n-type semiconductor layer and the n-type current distribution layer may be formed of the same gallium nitride-based semiconductor layer, the n-type current distribution layer is doped at a higher concentration than the first n-type semiconductor layer . The first n-type semiconductor layer and the n-type current dispersion layer may be GaN, and the n-type energy barrier layer may be AlGaN.

Meanwhile, a gallium nitride based second p-type semiconductor layer may be interposed between the first p-type semiconductor layer and the active layer.

In addition, an n-type electrode pad may be formed on one region of the first n-type semiconductor layer, and a p-type electrode pad may be formed on the first p-type semiconductor layer.

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 numbers refer to like elements throughout.

3 is a cross-sectional view illustrating a light emitting diode having an energy barrier layer for current distribution according to an embodiment of the present invention.

Referring to FIG. 3, an active layer 61 is interposed between a gallium nitride series first n-type semiconductor layer 55 and a gallium nitride series first p-type semiconductor layer 65. The first n-type semiconductor layer 55 and the first p-type semiconductor layer 65 become n contact layers and p contact layers of light emitting diodes, respectively. A gallium nitride based second n-type semiconductor layer 59 is interposed between the first n-type semiconductor layer 55 and the active layer 61. In addition, an n-type energy barrier layer 57 is interposed between the first n-type semiconductor layer 55 and the second n-type semiconductor layer 59. The n-type energy barrier layer 57 is formed of a gallium nitride-based semiconductor layer having a larger energy band gap than the first n-type semiconductor layer 55.

Since the n-type energy barrier layer 57 has a larger energy band gap than the first n-type semiconductor layer 55, the first n-type semiconductor is provided between the energy barrier layer 57 and the first n-type semiconductor layer 55. An energy barrier is formed for electrons traveling in layer 55 toward active layer 61.

Here, the gallium nitride-based semiconductor layer means a bicomponent, tricomponent or quaternary nitride semiconductor layer represented by (B, Al, Ga, In) N. The n-type semiconductor layer may be formed by doping Si, and the p-type semiconductor layer may be formed by doping Mg.

It is preferable that the second n-type semiconductor layer 59 has a smaller energy band gap than the n-type energy barrier layer 57. The formation of an energy barrier between the n-type energy barrier layer 57 and the second n-type semiconductor layer 59 is prevented for electrons traveling through the n-type energy barrier layer 57 to the active layer 61.

The first n-type semiconductor layer 55 and the second n-type semiconductor layer 59 may be GaN. In addition, the energy barrier layer 57 may be AlGaN. AlGaN may be grown at a growth temperature that is substantially the same as the growth temperature of GaN, and by controlling the content of Al, the crystalline of the active layer 61 may be prevented from deteriorating.

The active layer 61 may have a single quantum well or multiple quantum well structure formed of a gallium nitride-based semiconductor layer. For example, the active layer 61 may be a multi quantum well in which InGaN layers and GaN layers are periodically stacked.

Meanwhile, a gallium nitride based second p-type semiconductor layer 63 may be interposed between the first p-type semiconductor layer 65 and the active layer 61. The first p-type semiconductor layer 65 may be GaN, and the second p-type semiconductor layer 63 may be AlGaN.

In addition, an n-type electrode pad 71 is formed on one region of the first n-type semiconductor layer 55, and a p-type electrode pad 69 is formed on the first p-type semiconductor layer 65. Can be. The electrode pads 69 and 71 are for connecting a light emitting diode to an external power source. For example, bonding wires may be bonded to the electrode pads 69 and 71. Meanwhile, an electrode layer 67 may be positioned between the p-type electrode pad 69 and the first p-type semiconductor layer 55, and the electrode layer 67 may be a transparent electrode such as Ni / Au or ITO.

The first n-type semiconductor layer 55 and the energy barrier layer 57 may be adjacent to each other. Alternatively, the first n-type semiconductor layer may be a heavily doped gallium nitride-based n-type current spreading layer 56. It may be interposed between the 55 and the n-type energy barrier layer (57). The energy band gap of the n-type current spreading layer 56 may be smaller than or equal to the energy band gap of the first n-type semiconductor layer 55. In this case, the n-type current spreading layer 56 is adjacent to the n-type energy barrier layer 57.

The n-type current spreading layer 56 may be formed of the same gallium nitride-based semiconductor layer as the first n-type semiconductor layer 55, except that the n-type current spreading layer 56 is the first n-type. It is doped at a higher concentration than the semiconductor layer 55. Accordingly, when the first n-type semiconductor layer 55 is GaN, the n-type current spreading layer 56 may also be GaN, and the n-type energy barrier layer 57 may be AlGaN.

The semiconductor layers may be located on the substrate 51. The substrate 51 may be a substrate of various materials such as sapphire, silicon carbide (SiC), and spinel. Meanwhile, a buffer layer 53 or a nucleation layer may be interposed between the first n-type semiconductor layer 55 and the substrate 51. The buffer layer 53 mitigates lattice mismatch between the substrate 51 and the first n-type semiconductor layer 55 to reduce crystal defects. In addition, the buffer layer 53 may be formed of a gallium nitride-based semiconductor layer, for example, GaN or AlGaN.

In the present embodiment, the gallium nitride-based semiconductor layers may be grown on the substrate 51 using metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy, or the like. have. In addition, the grown semiconductor layers may be etched using photolithography and etching techniques to expose a portion of the first n-type semiconductor layer 55, and an n-type electrode on the exposed first n-type semiconductor layer 55. Pad 71 is formed. On the other hand, the electrode layer 67 is formed on the first p-type semiconductor layer 65, and the p-type electrode pad 69 is formed thereon. The electrode pads 69 and 71 may be formed using a lift-off process.

4 is an energy band diagram based on the energy barrier layer 57 of a light emitting diode according to an embodiment of the present invention. Here, the first n-type semiconductor layer 55 and the n-type energy barrier layer 57 is adjacent to each other, the first n-type semiconductor layer 55 and the second n-type semiconductor layer 59 is GaN, n-type The case where the energy barrier layer 57 is AlGaN will be described as an example.

Referring to FIG. 4, the first n-type semiconductor layer 55 and the second n-type semiconductor layer 59 have a smaller energy band gap than the n-type energy barrier layer 57. Thus, the n-type energy barrier layer 57 has a wide energy band, as shown, between the first and second n-type semiconductor layers 55, 59.

When an external power source is connected to the electrode pads 69 and 71 of FIG. 3 and a forward voltage is applied to the light emitting diode, holes are formed through the first p-type semiconductor layer 65 in the p-type electrode pad 69. The electrons are introduced into the active layer 61, and electrons are introduced into the active layer 61 through the first n-type semiconductor layer 55 from the n-type electrode pad 71 so that holes and holes are coupled to the active layer. Therefore, electrons flow through the n-type energy barrier layer 57 and the second n-type semiconductor layer 59 from the first n-type semiconductor layer 55 to the active layer 61.

The electrons traveling from the first n-type semiconductor layer 55 to the n-type energy barrier layer 57 are at their interface due to the difference in energy band gap between the n-type semiconductor layer 55 and the n-type energy barrier layer 57. Experience the energy barrier Therefore, after electrons are accumulated and uniformly distributed in the first n-type semiconductor layer 55, the active layer 61 flows through the energy barrier layer 57 and the second n-type semiconductor layer 59 and enters the active layer 61. Electrons are introduced over the entire area of 61.

As a result, the electrons are evenly distributed by the energy barrier layer 57, thereby preventing current crowding, and light is generated in all regions within the active layer 61. The current concentrating phenomenon generates light in a limited portion of the active layer 61, thereby increasing the forward voltage, reducing the luminous efficiency, and causing local overheating, thereby shortening the lifespan of the light emitting diode. However, according to the present embodiment, since such a current concentration phenomenon can be prevented, it is possible to improve the lifespan and luminous efficiency of the light emitting diode.

5 is an energy band diagram of a light emitting diode further comprising an n-type current spreading layer 56. Herein, the n-type current spreading layer 56 and the n-type energy barrier layer 57 are adjacent to each other, and the first n-type semiconductor layer 55, the n-type current spreading layer 56, and the second n-type semiconductor layer ( 59 is GaN and the n-type energy barrier layer 57 is AlGaN.

Referring to FIG. 5, as described with reference to FIG. 4, an energy band gap of the energy barrier layer 57 is larger than an energy band gap of the first n-type semiconductor layer and the second n-type semiconductor layer, and is n-type. Larger than the energy bandgap of the current spreading layer 56. In addition, the n-type current spreading layer 56 has the same energy bandgap as the first and second n-type semiconductor layers. The n-type current spreading layer 56 may be formed of a semiconductor layer having a smaller energy band gap than the first n-type semiconductor layer.

On the other hand, since the n-type current spreading layer 56 is heavily doped, the Fermi energy level is higher than that of the first n-type semiconductor layer 57. Therefore, the energy band of the n-type current spreading layer 56 is slightly lower than the energy band of the first n-type semiconductor layer 55 as shown. That is, the n-type current spreading layer 56 forms a well for electrons between the first n-type semiconductor layer 55 and the energy barrier layer 57. The energy barrier between the n-type current spreading layer 56 and the energy barrier layer 57 is higher than the energy barrier between the first n-type semiconductor layer 55 and the energy barrier layer 57, and the n-type current spreading layer ( Since 56 is heavily doped, electrons can be dispersed more quickly within the n-type current spreading layer 56.

As a result, the luminous efficiency is improved by dispersing electrons traveling toward the active layer 61 more quickly through the n-type current spreading layer 56 between the first n-type semiconductor layer 55 and the energy barrier layer 57. It can be further improved.

According to embodiments of the present invention, it is possible to provide a light emitting diode capable of evenly dispersing electrons through an energy barrier layer between a first n-type semiconductor layer and a second n-type semiconductor layer, a gallium nitride-based semiconductor By appropriately selecting the layers, the semiconductor layers can be formed without significantly changing the growth temperature as compared with the prior art. In addition, the energy barrier layer can be doped at a high concentration, so that the series resistance of the light emitting diode can be prevented. In addition, electrons can be more quickly dispersed between the energy barrier layer and the first n-type semiconductor layer through the n-type current spreading layer, thereby further improving luminous efficiency.

In addition, according to embodiments of the present invention, it is possible to prevent the current concentration phenomenon to prevent the increase in the forward voltage due to the current concentration phenomenon, it is possible to prevent the local overheating to extend the life of the light emitting diode.

Claims (8)

A gallium nitride-based first n-type semiconductor layer; Gallium nitride-based first p-type semiconductor layers; An active layer interposed between the first n-type semiconductor layer and the first p-type semiconductor layer; A gallium nitride based second n-type semiconductor layer interposed between the first n-type semiconductor layer and the active layer; And a gallium nitride-based n-type energy barrier layer interposed between the first n-type semiconductor layer and the second n-type semiconductor layer and having an energy band gap greater than that of the first n-type semiconductor layer. The method according to claim 1, The second n-type semiconductor layer is light emitting diode, characterized in that the energy band gap is smaller than the n-type energy barrier layer. The method according to claim 2, Wherein the first n-type semiconductor layer and the second n-type semiconductor layer are GaN, and the energy barrier layer is AlGaN. The method according to claim 1, And further comprising a gallium nitride-based n-type current spreading layer heavily doped between the first n-type semiconductor layer and the n-type energy barrier layer, wherein an energy band gap of the n-type current spreading layer is the first n-type. A light emitting diode less than or equal to the energy bandgap of the semiconductor layer. The method according to claim 4, The first n-type semiconductor layer and the n-type current distribution layer is formed of the same gallium nitride-based semiconductor layer, wherein the n-type current distribution layer is doped with a higher concentration than the first n-type semiconductor layer. The method according to claim 5, Wherein the first n-type semiconductor layer and the n-type current spreading layer are GaN, and the n-type energy barrier layer is AlGaN. The method according to claim 1 or 4, And a gallium nitride based second p-type semiconductor layer interposed between the first p-type semiconductor layer and the active layer. The method according to claim 1, An n-type electrode pad formed on one region of the first n-type semiconductor layer; And The light emitting diode further comprises a p-type electrode pad formed on the first p-type semiconductor layer.

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