# Patent

## Title
Light emitting diode and fabrication method thereof

## Abstract

A light emitting diode (LED) and a method for fabricating the same, capable of improving brightness by forming a InGaN layer having a low concentration of indium, and whose lattice constant is similar to that of an active layer of the LED, is provided. The LED includes: a buffer layer disposed on a sapphire substrate; a GaN layer disposed on the buffer layer; a doped GaN layer disposed on the GaN layer; a GaN layer having indium disposed on the GaN layer; an active layer disposed on the GaN layer having indium; and a P-type GaN disposed on the active layer. Here, an empirical formula of the GaN layer having indium is given by In(x)Ga(1-x)N and a range of x is given by 0<x<2, and a thickness of the GaN layer having indium is 50-200 Å.

## Background
This application is a Continuation of application Ser. No. 11/889,549 filed on Aug. 14, 2007, U.S. Pat. No. 7,682,849 which is a Divisional of application Ser. No. 11/333,247 (now U.S. Pat. No. 7,531,827) filed on Jan. 18, 2006, and for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 2003/48993 filed in Korea on Jul. 18, 2003 under 35 U.S.C. §119; the entire contents of all are hereby incorporated by reference.


TECHNICAL FIELD
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode and a fabrication method thereof in which a light efficiency can be improved by forming a layer containing indium (In), whose lattice constant is similar to that of an active layer formed in the LED.
BACKGROUND ART
Generally, a light emitting diode (LED) is a kind of semiconductor device, and it converts an electrical signal into infrared ray or light by using a characteristic of a compound semiconductor, to send or receive a signal. The LED is used for home appliances, a remote controller, an electronic display board, a display device, a variety of automation apparatuses and the like.
An operation principle of the LED will be briefly described in the following.
When a forward voltage is applied to a semiconductor of a specific chemical element, electrons and holes are recombined with each other while moving through a positive-negative junction. The recombination of the electrons and the holes causes an energy level to fall down, so that light is emitted.
The LED is generally manufactured to have a very small size of 0.25 mm2 and is mounted on a printed circuit board (PCB) or a lead frame using an epoxy mold.
Representative of the LEDs is a plastic package of 5 mm (T 13⁄4) or a new package being developed in a specific application field.
A color of light emitted from the LED is determined by a wavelength obtained depending on a combination of elements constituting a semiconductor chip.
Particularly, as an information communication apparatus is in a trend of a small-size and slimness, the communication apparatus has more miniaturized parts such as a resistance, a condenser, and a noise filter. The LED is manufactured in a form of a surface mounted device (hereinafter, referred to as “SMD”) so as to be directly mounted on a printed circuit board (hereinafter, referred to as “PCB”).
Accordingly, an LED lamp for a display device is being developed in the form of the SMD. Such an SMD can substitute a related-art simple lamp. The SMD is used for a lamp display, a character display, an image display and the like that express various colors.
Further, as a high-density integration technology for a semiconductor device is developed and a consumer prefers a more compact electronic product, Semiconductor Mounting Technology (SMT) is widely used, and a packaging technology of the semiconductor device employs a technology for minimizing an installation space such as a Ball Grid Array (BGA), a wire bonding, and a flip chip bonding.
FIG. 1 is a view illustrating a process for fabricating a light emitting diode according to the related art.
As shown in FIG. 1, a gallium nitride (GaN) buffer layer 101 is formed on a sapphire substrate 100 formed of Al2O3. After that, a GaN layer 103, which is not doped with dopants (Hereinafter, referred to as “undoped”), is formed on the GaN buffer layer 101.
In order to form a Group 3-based element in a form of a thin film on the sapphire substrate 100 as described above, a metal organic chemical vapor deposition (MOCVD) is generally used. At this time, the thin film layer is formed under a constant growth pressure.
An N-type GaN layer 105 is formed on the undoped GaN layer 103, and silicon using silane (SiH4 or disilane (Si2H6) gases is used to form the N-type GaN layer 105.
After the N-type GaN layer 105 is formed, an active layer 109 is formed on the N-type GaN layer 105. The active layer 109 functioning as a light emission region is a semiconductor layer having an illuminant formed of a indium gallium nitride (InGaN).
After the active layer 109 is formed, a P-type GaN layer 110 is subsequently formed.
The P-type GaN layer 110 is in a contrast to the N-type GaN layer 105. Namely, electrons are drifted by an external voltage in the N-type GaN layer 105, while holes are drifted by the external voltage in the P-type GaN layer 110. Therefore, the holes and the electrons are mutually recombined in the active layer 109, thereby emitting light.
A transparent metal (TM) layer using a transparent Indium-Tin-Oxide (ITO) metal is formed on the P-type GaN layer 110 so that light generated at the active layer 109 is transmitted and emitted to the external.
After the TM layer is formed, a P-type electrode is formed to complete the LED.
However, the LED constructed as above has a drawback in that a strain is increased due to an inconsistency of the lattice constants between the InGaN layer of the active layer and the GaN layer, thereby reducing an amount of light generated in the active layer.
Further, the inconsistency of the lattice constant deteriorates a product reliability of the LED.
Also, there is a drawback in that the active layer, which is formed on the N-type GaN layer adjacent to the active layer in a form of a two-dimensional plane, has a lower luminous intensity than a three-dimensional formation.
DISCLOSURE OF THE INVENTION
Accordingly, the present invention is directed to an LED and a fabrication method thereof that substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an LED and a fabrication method thereof in which a GaN layer having a low concentration of indium (In) is formed between the active layer and an N-type GaN layer to reduce an inconsistency of lattice constants between an active layer and a GaN layer, thereby increasing a light efficiency and improving a product reliability.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a light emitting diode includes: a buffer layer disposed on a sapphire substrate; a GaN layer disposed on the buffer layer; an N-type GaN layer disposed on the GaN layer; a GaN layer having indium disposed on the N-type GaN layer; an active layer disposed on the GaN layer having indium; and a P-type GaN layer disposed on the active layer.
Here, an empirical formula of the GaN layer having indium is given by In(x)Ga(1-x)N and a range of x is given by 0<x<2, and a thickness of the GaN layer having indium is 50-200 Å.
Also, a GaN layer whose thickness is 10-30 Å is formed on the GaN layer having indium, and the active layer is of a multi-quantum well structure having a InGaN/GaN structure.
Also, a method for fabricating a LED according to the present invention, includes the steps of: forming a buffer layer on a sapphire substrate; forming a GaN layer on the buffer layer; forming an N-type GaN layer on the GaN layer; forming a GaN layer having indium on the N-type GaN layer; forming an active layer on the GaN layer having indium; and forming a P-type GaN layer on the active layer.
Here, after the GaN layer having indium is formed, a GaN layer is subsequently formed at a thickness of 10-30 Å, and the active layer is formed in 1 period to 7 periods under a temperature condition of 600-800° C.
Also, after the active layer is formed, the P-type GaN layer is formed at a thickness of 750-1500 Å at a temperature of 980-1020° C.
According to the present invention, the InGaN layer having a low concentration of indium is formed between the N-type GaN layer and the active layer formed on the sapphire substrate, so that deterioration of light efficiency due to inconsistency of a lattice constant between the GaN layer and the active layer is prevented and the light efficiency can be improved.
Also, the InGaN layer having a low Indium composition has a three dimensional structure on its surface and such three-dimensional growth of the surface can improve the light efficiency even more.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view illustrating a process for fabricating an LED according to the related art;
FIGS. 2a through 2d are views illustrating a process for fabricating an LED according to the present invention; and
FIG. 3 is a view schematically showing a P-type GaN layer formed according to a quantum well growing method among the method for fabricating the LED according to the present invention.



BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings.
FIGS. 2a through 2d are views illustrating a process for fabricating a light emitting diode (LED) according to the present invention.
As shown in FIGS. 2a through 2d, a buffer layer 201 having an empirical formula of In(x)Ga(1-x)N is formed on a sapphire (Al2O3) substrate 200 at a temperature of 500-600° C., and an undoped GaN layer 203 is grown up to a thickness of 1-3 μm on the buffer layer 201 at a temperature of 1000-1100° C. (FIG. 2a).
Next, an N-type GaN layer 205 is grown up to a thickness of 1-3 μm on the undoped GaN layer 203 at a temperature of 1000-1100° C. (FIG. 2b).
After the N-type GaN layer 205 is formed, a GaN layer 207 having a low mole of indium (In) is grown up at a temperature of 600-800° C. before an active layer 209 is formed (FIG. 2c).
The composition ratio of indium in the InGaN layer 207 is given by In(x)Ga(1-x)N(0<x<0.2). The In(x)Ga(1-x)N(0<x<0.2) layer is grown up to a thickness of 50-200 Å.
After the InGaN layer 207 is formed, an active layer 209 is formed.
The active layer 209 is formed of GaN layer at a thickness of 10-30 Å and makes an electron tunnels into a quantum-well layer, thereby preventing holes from penetrating into the In(x)Ga(1-x)N(0<x<0.2) layer.
The active layer 209 of the InGaN/GaN having a multi-quantum-well structure is formed in 1 period to 7 periods at a temperature of 600-800° C.
After the active layer 209 is formed, a P-type GaN layer 210 doped with a dopant of magnesium (Mg) is formed grown up to a thickness of 750-1500 Å at a temperature of 980-1020° C.
FIG. 3 is a view schematically showing a P-type GaN layer formed according to a quantum-well growing method among the method for fabricating the LED according to the present invention.
As shown in FIG. 3, in the quantum-well growing method, a well growing step of forming a well layer 301 that includes various dopants such as In, Ga, and N is performed. Here, a growth condition of the well layer 301 is given by TMGa: 0-200 μmol/min, TMIn: 0-100 μmol/min, NH3: 0-80 L/min, growing temperature: 600-800° C.
Subsequently, an enough crystal time is given so that the dopants included in the step of growing the well layer 301 may combine each other completely to form a crystal layer 302, whereby a combining ability of In and N, Ga and N, In and Ga inside the well layer 301, is improved.
Here, a growth time of the crystal layer 302 is given by 0.1 sec-60 min and N2: 30-50 L/min, H2: 30-50 L/min.
Next, a barrier growing step of forming a barrier layer 303 including various dopants such as Ga, N, is performed. Here, a growth condition of the barrier layer 303 is given by TMGa: 100-500 μmol/min, TMIn: 50-200 μmol/min, NH3: 0-80 L/min, growing temperature: 600-800° C.
As described above, the active layer 209 is formed so as to have a multi-quantum well structure in the present invention, and the GaN layer 207 having the low concentration of indium is formed in a shallow thickness on the N-type GaN layer 205 at a low temperature, so that inconsistency of the lattice constant with the active layer 209 is reduced and light efficiency can be improved.
Also, since the InGaN layer of the active layer 209 is formed through a three-dimensional growth, a brightness of light generated at the active layer 209 is increased.
INDUSTRIAL APPLICABILITY
As described above in detail, the present invention forms the InGaN layer having a low concentration of indium between the N-type GaN layer and the active layer formed on the sapphire substrate, thereby reducing inconsistency of the lattice constant with the active layer and improving light efficiency.
Further, the InGaN layer having the low concentration of indium, has a three dimensional structure on its surface, and light efficiency can be improved even more in case a surface has such a three-dimensional structure.
While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

## Claims

1. A method for fabricating a light emitting diode, comprising:
forming a first conductive type semiconductor layer;
forming at least one GaN layer having indium directly on the first conductive type semiconductor layer;
forming at least one GaN layer directly on the at least one GaN layer having indium;
forming an active layer directly on the at least one GaN layer, wherein the active layer is formed of a multi-quantum well structure having an InGaN layer and a GaN layer; and
forming a second conductive type semiconductor layer on the active layer, wherein the second conductive type semiconductor layer has a thickness of 750-1500 Å.

2. The method according to claim 1, wherein an empirical formula of the at least one GaN layer having indium is given by InxGa1-xN and a range of x is given by 0<x<0.2.

3. The method according to claim 1, wherein a thickness of the at least one GaN layer is 10-30 Å.

4. The method according to claim 1, wherein a thickness of the first conductive type semiconductor layer is 1-3 μm.

5. The method according to claim 1, wherein the active layer includes at least one well layer and at least one barrier layer formed in 1 period to 7 periods.

6. The method according to claim 1, further comprising:
preparing a substrate;
forming a buffer layer on the substrate; and
forming a first GaN layer on the buffer layer.

7. The method according to claim 6, wherein the buffer layer is formed of GaN-based material.

8. The method according to claim 6, wherein a thickness of the first GaN layer is 1-3 μm.

9. The method according to claim 6, wherein a total thickness of the first GaN layer and the first conductive type semiconductor layer is 2-6 μm.

10. The method according to claim 6, wherein the first GaN layer includes an undoped GaN layer.

11. The method according to claim 1, further comprising:
forming a transparent metal on the second conductive type semiconductor layer, wherein the transparent metal is ITO (Indium-Tin-Oxide).

12. The method according to claim 1, wherein the second conductive type semiconductor layer includes at least one well layer and at least one barrier layer.

13. The method according to claim 1, wherein the at least one GaN layer having indium has a thickness less than 200 Å.

14. The method according to claim 13, wherein the at least one GaN layer having indium has a thickness greater than 50 Å and less than 200 Å.

15. A method for fabricating a light emitting diode, comprising:
preparing a substrate;
forming a buffer layer on the substrate;
forming a first GaN layer on the buffer layer;
forming a first conductive type semiconductor layer on the first GaN layer;
forming at least one GaN layer having indium directly on the first conductive type semiconductor layer;
forming at least one second GaN layer directly on the at least one GaN layer having indium;
forming an active layer directly on the at least one second GaN layer, wherein the active layer is formed of a multi-quantum well structure having an InGaN layer and a GaN layer; and
forming a second conductive type semiconductor layer on the active layer,
wherein a total thickness of the first GaN layer and the first conductive type semiconductor layer is 2-6 μm.

16. The method according to claim 15, wherein a thickness of the at least one second GaN layer is 10-30 Å.

17. The method according to claim 15, wherein the at least one GaN layer having indium has a thickness less than 200 Å.

18. The method according to claim 17, wherein the at least one GaN layer having indium has a thickness greater than 50 Å and less than 200 Å.

19. A method for fabricating a light emitting diode, comprising:
forming a first conductive type semiconductor layer;
forming at least one GaN layer having indium directly on the first conductive type semiconductor layer;
forming at least one GaN layer directly on the at least one GaN layer having indium, wherein a thickness of the at least one GaN layer is 10-30 Å;
forming an active layer including InGaN directly on the at least one GaN layer, wherein the active layer includes at least one well layer and at least one barrier layer, and wherein the active layer is formed of a multi-quantum well structure having an InGaN layer and a GaN layer; and
forming a second conductive type semiconductor layer on the active layer, wherein the second conductive type semiconductor layer has a thickness of 750-1500 Å.