KR101373804B1 - White light emitting diode and fabrication method thereof - Google Patents

Abstract

Provided are a white light emitting diode and a method of manufacturing the same. A white light emitting diode is formed by sequentially stacking an n-type semiconductor layer, a first active layer emitting green light, a second active layer emitting blue light, and a p-type semiconductor layer on a substrate, and the first active layer and the second active layer are quantum wells, respectively. The layer and the quantum barrier layer are alternately stacked, and the quantum barrier layer of the first active layer and the quantum barrier layer of the second active layer are n or p doped irrespective of each other. Therefore, by applying selective doping of n-type and p-type to the quantum barrier layer, it is possible to improve the internal quantum efficiency by improving the non-uniform carrier distribution problem in the active layer.

Description

White light emitting diode and manufacturing method thereof

The present invention relates to a light emitting diode, and more particularly to a white light emitting diode and a method of manufacturing the same.

A light-emitting diode (LED) is a type of p-n junction diode, and is a semiconductor device using electroluminescence, which is a phenomenon in which monochromatic light is emitted when voltage is applied in the forward direction.

The operation of the light emitting diode is a mechanism in which a voltage is applied to two electrodes represented by an anode and a cathode, and a light emitting operation is performed by supplying a current according to application of a voltage. In particular, an n-type semiconductor layer and a p-type semiconductor layer are in contact with the upper and lower portions of the active layer in which the multi-quantum well structure is formed. The n-type semiconductor layer supplies electrons to the active layer, and the p-type semiconductor layer supplies holes to the active layer. Electrons and holes injected into the multi-quantum well structure are defined inside the well layer by the quantum confinement effect, and light emission operation is performed by recombination.

In general, a gallium nitride-based white light emitting diode is manufactured by combining a light emitting diode emitting blue or ultraviolet light and a phosphor. However, in the case of a white light emitting diode using a phosphor, the luminous efficiency is lowered due to damage of the phosphor when used for a long time. In addition, there is a complex problem in the packaging process for manufacturing the device.

In order to overcome this problem, many researches have been conducted on white light emitting diodes that do not use phosphors by applying two or three light emitting active layers. Such white light emitting diodes are usually constructed by vertically stacking active layers emitting blue and green light. However, due to the difference in mobility between electrons and holes, a non-uniform carrier distribution is formed in the two active layer regions due to the current injection, thus there is a limit in improving the luminous efficiency.

The problem to be solved by the present invention is to provide a high-efficiency white light emitting diode structure that can increase the coupling efficiency of electrons and holes.

Another object of the present invention is to provide a method for manufacturing a high efficiency white light emitting diode.

One aspect of the present invention to achieve the above object provides a white light emitting diode. The white light emitting diode includes a substrate, an n-type semiconductor layer formed on the substrate, a first active layer emitting green light formed on the n-type semiconductor layer, a second active layer emitting blue light formed on the first active layer, and the first active layer. 2, a p-type semiconductor layer formed on the active layer, wherein the first active layer and the second active layer each have a structure in which a quantum well layer and a quantum barrier layer are alternately stacked, and a quantum barrier layer and a second active layer of the first active layer The quantum barrier layer is characterized in that n or p doped irrespective of each other.

The first active layer and the second active layer may be formed by alternately stacking an In _x Ga _{1 - x} N quantum well layer (0 <x <1) and a GaN quantum barrier layer, respectively.

Specifically, the quantum barrier layer of the first active layer is n-doped and the quantum barrier layer of the second active layer is p-doped, or the quantum barrier layer of the first active layer is p-doped and the quantum barrier layer of the second active layer is n Can be doped.

The white light emitting diode may further include a buffer layer between the substrate and the n-type semiconductor layer.

The white light emitting diode may further include an electron blocking layer between the second active layer and the p-type semiconductor layer.

Another aspect of the present invention to achieve the above object provides a method of manufacturing a white light emitting diode. The white light emitting diode manufacturing method comprises the steps of preparing a substrate, forming an n-type semiconductor layer on the substrate, forming a first active layer for emitting green light on the n-type semiconductor layer, on the first active layer Forming a second active layer that emits blue light in and forming a p-type semiconductor layer on the second active layer, wherein the first and second active layers alternate quantum well layers and quantum barrier layers, respectively. And the quantum barrier layer of the first active layer and the quantum barrier layer of the second active layer are n or p doped irrespective of each other.

According to the present invention, by applying selective doping of n-type and p-type to quantum barrier layers (QBs) to improve the non-uniform carrier distribution problem in the active layer to improve the internal quantum efficiency (IQE) Can be.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a cross-sectional view of a light emitting diode according to an embodiment of the present invention.
2 is an energy band diagram of a white light emitting diode with an undoped quantum barrier layer.
3 is an energy band diagram of a white light emitting diode having an n-type doped quantum barrier layer.
4 is an energy band diagram of a white light emitting diode having a p-type doped quantum barrier layer.
5 is a graph showing the internal quantum efficiency of the light emitting diode according to the doping effect of the quantum barrier layer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood, however, that the present invention is not limited to the embodiments described herein but may be embodied in other forms and includes all equivalents and alternatives falling within the spirit and scope of the present invention.

When a layer is referred to herein as being "on" another layer or substrate, it may be formed directly on another layer or substrate, or a third layer may be interposed therebetween. In the present specification, directional expressions of the upper side, upper side, upper side, and the like can be understood as meaning lower, lower, lower, and the like according to the standard. That is, the expression of the spatial direction should be understood in the relative direction and should not be construed as limiting in the absolute direction. Also, it is to be understood that the terms “first”, “second” or “third” are used to distinguish between elements, rather than to impose any limitation on the elements.

In the drawings, the thicknesses of the layers and regions may be exaggerated or reduced for clarity. Like numbers refer to like elements throughout.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

1 is a cross-sectional view showing a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, a light emitting diode includes a substrate 100, a buffer layer 200, an n-type semiconductor layer 300, a first active layer 400, a second active layer 500, an electron blocking layer 600, and a p-type. The semiconductor layer 700 is included.

The substrate 100 may be any material as long as it has a predetermined light transmittance and may facilitate growth of the n-type semiconductor layer. For example, when the light emitting structure is formed of a nitride semiconductor compound semiconductor and has a hexagonal structure, it is preferable that the substrate 100 also has a hexagonal crystal structure. In addition, the substrate 100 may be provided in a form in which a single crystal thin film is provided thereon in a state in which a crystal structure other than an amorphous phase or a hexagonal system is provided. In addition, the substrate 100 may be provided in the form of a nanostructure formed on any substrate. The nanostructure may have a pattern shape. For example, the substrate 100 may be a sapphire (Al ₂ O ₃ ) substrate, a silicon carbide (SiC) substrate, a GaN substrate, a ZnO substrate or a silicon substrate.

A buffer layer 200 is formed on the substrate 100. The buffer layer 200 may be formed of a nitride film or an oxide film. The buffer layer 200 is provided to minimize the occurrence of crystal defects due to a mismatch between a lattice constant and a thermal expansion coefficient between the substrate and the n-type semiconductor layer. For example, after forming a low temperature GaN buffer layer on a sapphire substrate, a high quality single crystal GaN nitride semiconductor layer may be grown on the GaN buffer layer. However, the buffer layer 200 may be omitted according to the embodiment. For example, when an n-GaN semiconductor layer is grown on a GaN substrate, there is no problem of mismatch of lattice constant, and thus, it is sufficient that an additional buffer layer is not interposed between the GaN substrate and the n-GaN semiconductor layer.

The buffer layer 200 may be formed using a metal organic chemical vapor deposition (MOCVD) method, a low pressure chemical vapor deposition (LPCVD) method, or a molecular beam epitaxy (MBE) method.

An n-type semiconductor layer 300 is formed on the buffer layer 200. The n-type semiconductor layer 300 may be a nitride semiconductor. The nitride semiconductor may be composed of GaN. In this case, a Group 4 element may be used as the dopant, and Si is preferably used as the dopant.

The first active layer 400 and the second active layer 500 are sequentially formed on the n-type semiconductor layer 300. The active layers 400 and 500 may be formed of a material having a crystal structure that is the same as that of the lower n-type semiconductor layer 300. For example, when the n-type semiconductor layer is GaN-based, it is preferable to form the active layer also GaN-based.

The active layers 400 and 500 may have a multi quantum well structure. The multi quantum well structure refers to a structure in which a quantum barrier layer and a quantum well layer are alternately stacked. The quantum barrier layer has a band gap higher than that of the quantum well layer. Through this, the quantum confinement effect in the quantum well layer is effectively expressed. Formation of the quantum well layer or the quantum barrier layer is performed by bandgap engineering.

For example, the first active layer 400 and the second active layer 500 may each be an In _x Ga _{1 - x} N quantum well layer (0 <x <1) 420, 520 and a GaN quantum barrier layer 410, 510. ) May be composed of alternating stacked structures. In this case, the first active layer 400 may emit green light, and the second active layer 500 may emit blue light, so that the x value of each quantum well layer may be adjusted.

In general, due to the difference in mobility between electrons and holes, a nonuniform carrier distribution occurs in the active layer. Accordingly, in order to solve the above problem, according to the present invention, the quantum barrier layer 410 of the first active layer 400 and the quantum barrier layer 510 of the second active layer 500 may have n or p doping irrespective of each other. Apply. For example, when the quantum barrier layers 410 and 510 are made of GaN series, a Group 4 element may be used as the n-type dopant, for example, Si may be used as the dopant. In addition, a Group 2 element may be used as the p-type dopant, for example, Mg may be used as the dopant.

Preferably, one of the quantum barrier layer 410 of the first active layer 400 and the quantum barrier layer 510 of the second active layer 500 may be n-type doped, and the other may be doped p-type. .

Therefore, when using an active layer structure including an n- or p-doped quantum barrier layer, it is possible to minimize the non-uniformity of the carrier distribution.

2 is an energy band diagram of a white light emitting diode with an undoped quantum barrier layer. FIG. 3 is an energy band diagram of a white light emitting diode having an n-type doped quantum barrier layer, and FIG. 4 is an energy band diagram of a white light emitting diode having a p-type doped quantum barrier layer.

2 to 4, the band structure of the quantum barrier layer is bent downward when the quantum barrier layer is n-doped (FIG. 3), compared with the case where the quantum barrier layer is not doped (FIG. 2). It can be seen that the phenomenon appears. Therefore, as the height of the barrier layer in the conduction band is lowered, the injection of electrons is improved, so that electrical characteristics may be improved. However, as the current injection increases, the overflow phenomenon of the electron becomes worse and thus the optical characteristics may be degraded. On the other hand, when the quantum barrier layer is doped to the p-type (Fig. 4) it can be seen that the phenomenon that the band structure of the quantum barrier layer is bent upwards. As a result, efficient hole injection can be performed, thereby improving optical characteristics. However, as the height of the barrier layer increases in the conduction band, a problem may occur in which electrical characteristics are degraded.

Therefore, by selectively doping the n dopant and p dopant in the quantum barrier layer of the active layer that emits light of green and blue wavelength, respectively, it is possible to complement both optical and electrical properties.

Referring back to FIG. 1, for example, the quantum barrier layer 410 of the first active layer 400 is n-doped, and the quantum barrier layer 510 of the second active layer 500 is p-doped. Can be. In this case, the first active layer 400 and the second active layer 500 may be active layers emitting green light and blue light, respectively. The active layer emitting green light is difficult to move electrons because the restraining effect in the quantum well structure is larger than the active layer emitting blue light. However, when n-doped the quantum barrier layer of the active layer that emits green light, the barrier in the conduction band is lowered to facilitate electron transfer, thereby improving the electrical characteristics of the device. In addition, when p-doped the quantum barrier layer of the active layer that emits blue light can improve the hole injection efficiency, it is possible to prevent the electron overflow phenomenon due to the high barrier in the conduction band.

As another example, the quantum barrier layer 410 of the first active layer 400 may be p-doped, and the quantum barrier layer 510 of the second active layer 500 may be n-doped. In this case, the first active layer 400 and the second active layer 500 may be active layers emitting green light and blue light, respectively. In the light emitting diode, since the holes have a lower mobility than the electrons, the concentration of holes rapidly decreases toward the n-type semiconductor layer 300, resulting in uneven carrier distribution. However, when p-doped the quantum barrier layer of the active layer that emits green light enables efficient hole injection, thereby increasing the relatively low green light efficiency, thereby achieving stable white light. In this case, however, the barrier in the conduction band of the active layer emitting green light may be increased, thereby making it difficult to inject electrons into the active layer emitting blue light. However, this problem may be solved by n doping the quantum barrier layer of the active layer emitting blue light. .

The n or p doping to the quantum barrier layer may be performed using a conventionally known method such as ion implantation.

An electron blocking layer 600 is formed on the second active layer 500. The electron blocking layer 600 may be an Al _x Ga _{1 - x} N layer (0 <x <1). The electron blocking layer 600 performs a function of preventing the overflow of electrons. However, the electron blocking layer 600 may be omitted.

The p-type semiconductor layer 700 is formed on the electron blocking layer 600. The p-type semiconductor layer 700 is preferably formed of the same material as the base material forming the n-type semiconductor layer 300 or the active layer (400, 500). For example, when the n-type semiconductor layer 300 or the active layers 400 and 500 include GaN, it is preferable that the p-type semiconductor layer 700 also includes GaN. However, the material of the p-type semiconductor layer 700 is a material having a structure and a bandgap that can minimize the absorption of light formed in the active layer (400, 500), if the material having a predetermined light transmittance is used without limitation It is possible.

Various types of dopants may be introduced to form the p-type semiconductor layer 700. For example, when the p-type semiconductor layer 700 includes GaN, a Group 2 element may be used as the dopant, and Mg is preferably used.

The n-type semiconductor layer 300, the first active layer 400, the second active layer 500, the electron blocking layer 600, and the p-type semiconductor layer 700 are independent of MOCVD, HVPE, MBE, and E−. It may be formed using a beam or sputtering.

Hereinafter, preferred examples for the understanding of the present invention will be described. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

Manufacturing example  One

A white light emitting diode according to an embodiment of the present invention was prepared.

First, an undoped GaN layer having a thickness of about 3.5 μm was deposited on the sapphire substrate to mitigate lattice mismatch between the substrate and the semiconductor layer.

Next, an n-GaN layer was deposited on the undoped GaN layer by 2 mu m thickness using MOCVD. At this time, the n doping concentration was 5 x 10 ¹⁸ / cm ³ .

On the n-GaN layer, a GaN quantum barrier layer (10 nm) and an InGaN quantum well layer (3 nm) were alternately stacked on the n-GaN layer to form a first active layer emitting green light.

Here, after stacking the GaN quantum barrier layer, and before stacking the InGaN quantum well layer, n-doped the quantum barrier layer using a Si dopant. The n doping concentration of the quantum barrier layer was 3 x 10 ¹⁸ / cm ³ .

The GaN quantum barrier layer (10 nm) and the InGaN quantum well layer (3 nm) were alternately stacked on the first active layer by using MOCVD to form a second active layer emitting blue light.

Here, after stacking the GaN quantum barrier layer, and before stacking the InGaN quantum well layer, n-doped the quantum barrier layer using a Si dopant. The n doping concentration of the quantum barrier layer was 3 x 10 ¹⁸ / cm ³ .

A 30 nm thick p-AlGaN electron blocking layer and a 200 nm thick p-GaN semiconductor layer were sequentially formed on the second active layer by MOCVD. The p doping concentration of the electron blocking layer was 1.5 x 10 ¹⁹ / cm ^3, and the p doping concentration of the p-GaN semiconductor layer was 2 x 10 ¹⁹ / cm ³ .

Manufacturing example  2

A white light emitting diode was manufactured by the same method as Preparation Example 1, except that both the quantum barrier layer of the first active layer and the quantum barrier layer of the second active layer were p-type doped with Mg dopant.

Manufacturing example  3

The same method as in Preparation Example 1 was repeated except that the quantum barrier layer of the first active layer was n-type doped with Si dopant, and the quantum barrier layer of the second active layer was p-type doped with Mg dopant. A white light emitting diode was produced by the process.

Manufacturing example  4

The same method as in Preparation Example 1 was performed except that p-type Mg dopant was doped into the quantum barrier layer of the first active layer, and n-type doped was used to form the quantum barrier layer of the second active layer. A white light emitting diode was prepared.

Comparative Example

A white light emitting diode was manufactured in the same manner as in Preparation Example 1, except that the quantum barrier layers of the first active layer and the second active layer were undoped.

Analysis example

Internal quantum efficiency (IQE) of the white light emitting diodes manufactured according to Preparation Examples 1 to 4 and Comparative Examples was measured.

5 is a graph showing the internal quantum efficiency of the light emitting diode according to the doping effect of the quantum barrier layer.

Referring to FIG. 5, in the case where the quantum barrier layer of the first active layer is p-doped and the quantum barrier layer of the second active layer is n-doped (manufacture example 4) at low current density, the quantum barrier layer is undoped. It can be seen that the internal quantum efficiency is improved compared to the white light emitting diode.

In addition, when the quantum barrier layer of the first active layer is n-type doped and the quantum barrier layer of the second active layer is p-doped (Manufacturing Example 3) at a high current density, the white light emitting diode of the comparative example in which the quantum barrier layer is undoped In comparison, it can be seen that the internal quantum efficiency is improved.

This is judged to be due to the relatively uniform carrier distribution in the multi-quantum well structure.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, This is possible.

100: substrate 200: buffer layer
300: n-type semiconductor layer 400: first active layer
410: quantum barrier layer 420: quantum well layer
500: second active layer 510: quantum barrier layer
520: quantum well layer 600: electron blocking layer
700: p-type semiconductor layer

Claims (10)

Board;
An n-type semiconductor layer formed on the substrate;
A first active layer emitting green light formed on the n-type semiconductor layer;
A second active layer emitting blue light formed on the first active layer; And
A p-type semiconductor layer formed on the second active layer,
The first active layer and the second active layer have a structure in which quantum well layers and quantum barrier layers are alternately stacked, respectively.
The quantum barrier layer of the first active layer is p doped, the quantum barrier layer of the second active layer is n or p doped,
Or the quantum barrier layer of the first active layer is n-doped, and the quantum barrier layer of the second active layer is p-doped. The method of claim 1,
The first active layer and the second active layer are white light emitting diodes, characterized in that the In _x Ga _{1 - x} N quantum well layer (0 <x <1) and the GaN quantum barrier layer are alternately stacked. delete delete The method of claim 1,
And a buffer layer between the substrate and the n-type semiconductor layer. The method of claim 1,
The white light emitting diode of claim 2, further comprising an electron blocking layer between the second active layer and the p-type semiconductor layer. The method according to claim 6,
The electron blocking layer is an Al _x Ga _{1 - x} N layer (0 <x <1) characterized in that the white light emitting diode. Preparing a substrate;
Forming an n-type semiconductor layer on the substrate;
Forming a first active layer emitting green light on the n-type semiconductor layer;
Forming a second active layer emitting blue light on the first active layer; And
Forming a p-type semiconductor layer on the second active layer;
The first active layer and the second active layer are formed by alternately stacking quantum well layers and quantum barrier layers, respectively.
Forming the first active layer forms p-doped quantum barrier layers, and forming the second active layer forms n or p doped quantum barrier layers,
Alternatively, the forming of the first active layer may form n-doped quantum barrier layers, and the forming of the second active layer may form p-doped quantum barrier layers. delete delete

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