KR100935379B1

KR100935379B1 - Light emitting diode having active region of multi quantum well structure

Info

Publication number: KR100935379B1
Application number: KR20070132999A
Authority: KR
Inventors: 이동선; 황의진
Original assignee: 서울옵토디바이스주식회사
Priority date: 2007-12-18
Filing date: 2007-12-18
Publication date: 2010-01-08
Also published as: KR20090065612A

Abstract

A light emitting diode having an active region of a multi-quantum well structure is disclosed. This active region is located between the gallium nitride series N-type and P-type compound semiconductor layers and includes barrier layers with intentionally controlled thicknesses. Thus, efficient light emitting characteristics of the light emitting diode operating at low current and high current can be achieved.

Light Emitting Diode, Quantum Well, Gallium Nitride, Barrier Layer

Description

LIGHT EMITTING DIODE HAVING ACTIVE REGION OF MULTI QUANTUM WELL STRUCTURE}

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having an active region of a multi-quantum well structure that emits light efficiently under varying operating conditions by controlling the thickness of barrier layers.

In general, nitrides of Group III elements such as gallium nitride (GaN), aluminum nitride (AlN), and indium gallium nitride (InGaN) have excellent thermal stability and have a direct transition energy band structure. It is attracting much attention as a material for light emitting diodes in the ultraviolet region. In particular, indium gallium nitride (InGaN) compound semiconductors have attracted much attention due to their narrow band gap. Light emitting diodes using gallium nitride-based compound semiconductors are being used in various applications such as large-scale color flat panel display devices, backlight light sources, traffic lights, indoor lighting, high density light sources, high resolution output systems, and optical communications.

1 and 2 are cross-sectional and schematic band diagrams for explaining a light emitting diode having an active region of a conventional multi-quantum well structure.

1 and 2, the light emitting diode includes an N-type semiconductor layer 17 and a P-type semiconductor layer 21, and an active region between the N-type and P-type semiconductor layers 17 and 21. 19) is interposed.

The N-type semiconductor layer and the P-type semiconductor layer are formed of a nitride semiconductor layer of a group III element, such as GaN. On the other hand, the active region 19 is generally formed in a multi-quantum well structure in which the well layer 31 and the barrier layer 33 are alternately stacked. In an InGaN light emitting diode, an active region of a multi-quantum well structure is generally formed by alternately stacking an InGaN well layer 31 and an InGaN barrier layer 33. The well layer 31 is formed of a semiconductor layer having a smaller band gap than the N-type and P-type semiconductor layers 17 and 21 and the barrier layer 33 to provide a quantum well in which electrons and holes are recombined. In addition, Si may be doped into the barrier layers 33 to lower the driving voltage.

The light emitting diode according to the prior art employs barrier layers 33 of substantially the same thickness. The thickness of the barrier layers 33 is chosen to ensure process stability and to exhibit optimal luminescent properties under constant current conditions.

However, in some cases, the light emitting diode may operate under various current conditions. For example, in the case of an alternating light emitting diode driven by an alternating current power source, the light emitting diode may be driven by an alternating alternating current. In this case, the conventional light emitting diode made of the barrier layers 33 having the same thickness hardly exhibits optimum light emission characteristics simultaneously under low current and high current conditions.

The problem to be solved by the present invention is to provide a light emitting diode that can exhibit an efficient light emitting characteristics in an environment in which operating conditions change, such as alternating current.

In order to solve the above problems, the present invention provides a light emitting diode having an active region of a multi-quantum well structure. The light emitting diode according to the embodiments of the present invention is interposed between the gallium nitride-based N-type compound semiconductor layer, the gallium nitride-based P-type compound semiconductor layer, and the N-type and P-type compound semiconductor layers, and Barrier layers comprise an active region of a multi-quantum well structure in which alternating layers are stacked. The barrier layers are relatively thicker than the well layers, and barrier layers located between the well layers include the thinnest and thickest barrier layers.

Here, the thickness of the barrier layers is intentionally controlled, for example, the thickness of the thickest barrier layer may be in the range of 1.3 to 3 times the thickness of the thinnest barrier layer. Here, when the thickness difference is 1.3 times or less, it is difficult to improve the light emission characteristics by the thickness control, and when the thickness difference is 3 times or more, the barrier layer becomes excessively thick and it is difficult to lower the driving voltage.

Meanwhile, barrier layers positioned between the well layers may include a plurality of relatively thin barrier layers and a plurality of relatively thick barrier layers. The relatively thick barrier layers may have a thickness of 1.3 to 3 times that of the relatively thin barrier layers.

Thus, efficient light emission of the light emitting diode can be achieved by relatively thin barrier layers under low current and by relatively thick barrier layers under high current conditions.

The relatively thin barrier layers and the relatively thick barrier layers may be arranged in various ways. For example, the plurality of relatively thin barrier layers may be arranged close to each other, and the plurality of relatively thick barrier layers may be arranged close to each other. Alternatively, the plurality of relatively thin barrier layers and the plurality of relatively thick barrier layers may be alternately arranged.

In some embodiments of the present invention, the plurality of relatively thick barrier layers may be Si doped barrier layers. Accordingly, the resistivity of the relatively thick barrier layers can be lowered, thereby lowering the driving voltage.

In general, when doping Si to the barrier layers, the driving voltage can be lowered, but the luminance may decrease due to the doping of Si. Accordingly, the plurality of relatively thin barrier layers may be, but are not limited to, Si-doped barrier layers, and the Si concentration is lower than that of the Si-doped barrier layers or the plurality of relatively thick barrier layers. Barrier layers doped with

In still other embodiments of the present invention, each of the plurality of relatively thick barrier layers may be barrier layers partially doped with Si in a portion closer to the P-type compound semiconductor layer.

Meanwhile, barrier layers having various thicknesses between the thickness of the thinnest barrier layer and the thickness of the thickest barrier layer may be located between the well layers, and these barrier layers may be arranged in the order of thickest thickness in the active region or It may be arranged in the reverse order.

In addition, the thicker the barrier layers positioned between the well layers may be doped with Si at a higher concentration. Alternatively, barrier layers positioned between the well layers may be barrier layers partially doped with Si in a portion closer to the P-type compound semiconductor layer.

According to embodiments of the present invention, an active region including a relatively thick barrier layer and a relatively thin barrier layer may be adopted to provide a light emitting diode exhibiting efficient light emission characteristics under various operating conditions.

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 active region of a multi-quantum well structure according to an embodiment of the present invention, and FIG. 4 is a view showing an active region of a multi-quantum well structure according to an embodiment of the present invention. A schematic band diagram for describing a light emitting diode.

3 and 4, an N-type compound semiconductor layer 57 is positioned on the substrate 51. In addition, a buffer layer may be interposed between the substrate 51 and the N-type compound semiconductor layer 57, and the buffer layer may include a low temperature buffer layer 53 and a high temperature buffer layer 55. The substrate 51 is not particularly limited and may be, for example, sapphire, spinel, silicon carbide substrate, or the like. Meanwhile, the low temperature buffer layer 53 may be generally formed of Al _x Ga ₁ _- _x N (0 ≦ _x ≦ 1), and the high temperature buffer layer 55 may be, for example, N-type doped with undoped GaN or N-type impurities. GaN.

A P-type compound semiconductor layer 61 is positioned on the N-type compound semiconductor layer 57, and an active region 59 is interposed between the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 61. . The N-type compound semiconductor layer and the P-type compound semiconductor layer may be formed of a group III nitride semiconductor layer of (Al, In, Ga) N series. For example, the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 63 may be N-type and P-type GaN, or N-type and P-type AlGaN, respectively. In addition, a blocking layer (not shown) may be interposed between the P-type compound semiconductor layer 61 and the active region 59. The blocking layer may also be formed of a (Al, In, Ga) N-based group III nitride semiconductor layer, for example, AlGaN. In addition, another blocking layer (not shown) may be interposed between the N-type compound semiconductor layer 57 and the active region 59.

Meanwhile, the active region 59 has a multi-quantum well structure including well layers 71 and barrier layers 73, 75, 77, and 79 alternately stacked. The well layer 71 may be formed of InGaN, and its composition ratio may be selected according to the wavelength of light required.

Meanwhile, the barrier layers 73, 75, 77, and 79 are formed of a group III nitride semiconductor layer of (Al, In, Ga) N series having a larger band gap than the well layers 71, respectively. For example, it may be formed of an InGaN layer or a GaN layer.

In addition, barrier layers 77 and 79 are relatively thick compared to barrier layers 73 and 75. For example, the barrier layers 77 and 79 may have a thickness of 1.3 to 3 times that of the barrier layers 73 and 75. When the barrier layers 77 and 79 are less than 1.3 times that of the barrier layers 73 and 75, it is difficult to obtain an effect by thickness control, and when the barrier layers 77 and 79 are three times or more, the barrier layers 77 and 79 are Excessively thick, the driving voltage becomes excessively high.

Meanwhile, all of the barrier layers 73, 75, 77, and 79 may be doped with Si, and the driving voltage may be reduced by Si doping. In addition, the barrier layers may be all doped at the same concentration, but the present invention is not limited thereto. The barrier layers 73 and 75 may be doped at a lower concentration than the barrier layers 77 and 79. Alternatively, the barrier layers 73 and 75 may not be doped with Si. Since the barrier layers 73 and 75 have a relatively thin thickness, the increase in driving voltage is not large even if Si is not doped. In addition, by omitting Si doping, it is possible to prevent a decrease in luminance that may be caused by Si doping.

When Si is doped, Si may be doped over the entire thickness of barrier layer 73, 75, 77 or 79, but is not limited thereto and may be partially doped. In this case, in order to alleviate the piezo electric field, it is preferable that Si is partially doped in the portion of the barrier layer doped with Si closer to the P-type compound semiconductor layer with respect to the barrier layer.

In the present embodiment, although the relatively thin barrier layers 73 and 75 are arranged close to each other, and the relatively thick barrier layers 77 and 79 are arranged close to each other, it is not limited thereto. 5, relatively thin barrier layers 73 and 75 and relatively thick barrier layers 77 and 79 may be alternately arranged.

Also, in the present embodiment, four barrier layers are shown and described, but the number of barrier layers may be higher.

6 is a band diagram for describing a light emitting diode according to another embodiment of the present invention.

Referring to FIG. 6, substantially the same as the light emitting diode described with reference to FIGS. 3 and 4, except that the thickness of the barrier layers in the active region 59 is different.

That is, in this embodiment, the barrier layers 83, 85, 87, 89 located between the well layers 71 are not constant in thickness, and the thinnest barrier layer 83 and the thickest barrier layer ( The thickness varies between 89). Here, the thickness of the thickest barrier layer 89 is in the range of 1.3 to 3 times the thickness of the thinnest barrier layer 83.

In addition, the barrier layers may be arranged in the active area 59 in the order of thickness or vice versa.

According to the present embodiment, it is possible to provide a light emitting diode capable of efficiently emitting light for a variable operating condition by adjusting the thickness of each of the barrier layers in accordance with the change of the operating condition.

Meanwhile, the thicker the barrier layers 83, 85, 87, and 89 may be barrier layers doped with a high concentration of Si. In addition, barrier layers having a relatively thin thickness may be undoped or lightly doped with Si.

In addition, the barrier layers may include a barrier layer partially doped with Si in a portion closer to the P-type compound semiconductor layer. Partial doping of Si can mitigate strain in the well layer to reduce polarization by the piezo electric field, and can also minimize the decrease in luminance that can occur due to Si doping.

In the present embodiment, four barrier layers are shown and described, but not limited thereto, and a larger number of barrier layers may be alternately stacked with the well layer.

1 is a cross-sectional view illustrating a light emitting diode having an active region of a conventional multi-quantum well structure.

2 is a schematic band diagram for describing a light emitting diode having an active region of a conventional multi-quantum well structure.

3 is a cross-sectional view illustrating a light emitting diode having an active region of a multi-quantum well structure according to an exemplary embodiment of the present invention.

4 is a schematic band diagram for describing a light emitting diode having an active region of a multi-quantum well structure according to an embodiment of the present invention.

5 is a schematic band diagram for describing a light emitting diode having an active region of a multi-quantum well structure according to another exemplary embodiment of the present invention.

FIG. 6 is a schematic band diagram for describing a light emitting diode having an active region of a multi-quantum well structure according to another embodiment of the present invention.

Claims

Gallium nitride-based N-type compound semiconductor layers;

Gallium nitride-based P-type compound semiconductor layers; And

An active region interposed between the N-type and P-type compound semiconductor layers, and having a multi-quantum well structure in which well layers and barrier layers are alternately stacked;

The barrier layers are relatively thicker than the well layers,

Barrier layers located between the well layers include the thinnest barrier layer and the thickest barrier layer, wherein the thickness of the thickest barrier layer is in the range of 1.3 to 3 times the thickness of the thinnest barrier layer,

Wherein the thickest barrier layer has a higher Si doping concentration than the thinnest barrier layer.

The method according to claim 1,

Barrier layers located between the well layers,

At least one barrier layer having a thickness closer to the thickness of the thinnest barrier layer than the thickness of the thickest barrier layer; And

And at least one barrier layer having a thickness closer to the thickness of the thickest barrier layer than the thickness of the thinnest barrier layer.

The method according to claim 2,

At least one barrier layer having a thickness closer to the thickness of the thinnest barrier layer and the thinnest barrier layer is arranged close to each other and at least having a thickness closer to the thickness of the thickest barrier layer and the thickest barrier layer. A light emitting diode in which one barrier layer is arranged close to each other.

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The method according to claim 2,

At least one barrier layer having a thickness closer to that of the thickest barrier layer is a Si-doped barrier layer.

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The method according to claim 5,

At least one barrier layer having a thickness closer to the thickness of the thinnest barrier layer is lightly doped with Si compared to at least one barrier layer having a thickness closer to the thickness of the thickest barrier layer.

The method according to claim 2,

And the at least one barrier layer having a thickness closer to the thickness of the thickest barrier layer and the thickest barrier layer is a barrier layer partially doped with Si in a portion closer to the P-type compound semiconductor layer, respectively.

The method according to claim 2,

Barrier layers positioned between the well layers are arranged in the thickest order or vice versa in the active region.

The method according to claim 9,

The barrier layers positioned between the well layers are Si-doped light emitting diodes having a higher thickness.

The method according to claim 9,

The barrier layers positioned between the well layers include barrier layers partially doped with Si in a portion closer to the P-type compound semiconductor layer.