# Patent

## Title
Light-emitting device and manufacturing method thereof

## Abstract

Provides is a semiconductor light-emitting device. The semiconductor light-emitting device includes a first conduction-type cladding layer, an active layer, and a second conduction-type cladding layer, on a substrate. Portions of the substrate and the first conduction-type cladding layer are removed. According to the light-emitting device having the above-construction, damage to a grown epitaxial layer is reduced, and a size of an active layer increases, so that a light-emission efficiency increases. Even when a size of a light-emitting device is small, a short-circuit occurring between electrodes can be prevented. Further, brightness and reliability of the light-emitting device are improved.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device.
2. Description of the Related Art
Generally, a light-emitting device is a kind of a semiconductor device used for converting electricity into an infrared or light using a characteristic of a compound semiconductor to transmit and receive a signal. The light-emitting device is widely used for home appliances, remote controllers, display boards, display apparatuses, and a variety of automation apparatuses.
In operation, when a forward voltage is applied to a semiconductor formed of a predetermined element, an electron and a hole recombine at a positive-negative junction portion. At this point, an energy level falls down due to recombination of an electron-hole pair, so that light is emitted.
Also, a light-emitting device is generally manufactured in a very small size of 0.23 mm2, and provided in a structure in which the light-emitting device is mounted in a printed circuit board (PCB) using an epoxy mold and a lead frame. A light-emitting device most widely used currently is a 5-mm plastic package but is not limited thereto and a new type of package is under development depending on a predetermined application. A wavelength of light emitted from a light-emitting device is determined by a combination of elements constituting a semiconductor chip.
A related art nitride light-emitting device will be described with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of a related art light-emitting device. A light-emitting device, which will be described below, is a light-emitting device using a nitride semiconductor, specifically, a gallium nitride.
Referring to FIG. 1, the related art light-emitting device includes a buffer layer 20, un-doped GaN layer 30, an n-type first conduction-type cladding layer 40, an active layer 60, a p-type second conduction-type cladding layer 70, an n-type electrode 50, and a p-type electrode 80 sequentially formed on a substrate 10 exemplified as a sapphire substrate.
A method for manufacturing the related art light-emitting device is sequentially described in detail.
First, the buffer layer 20 is formed on the substrate 10 in order to grow high quality nitride, so that a planarization of the substrate 10 is increased. For example, melt-back etching caused by a chemical reaction of the substrate 10 is prevented.
Also, the un-doped GaN layer 30 grows the n-type first conduction-type cladding layer 40 thereon, as a base layer for various semiconductor layers to be formed on the buffer layer 20.
Subsequently, the active layer 60 and the p-type second conduction-type cladding layer 70 are grown on the n-type first conduction-type cladding layer 40.
Here, the active layer 60 having a multiple quantum well (MQW) structure is a layer where holes flowing through the p-type electrode 80 and electrons flowing through the n-type electrode 50 recombine, thereby emitting light.
With this state, the n-type electrode 50 is electrically connected on an upper portion of the n-type first conduction-type cladding layer 40, which is a portion on which the p-type second conduction-type cladding layer 70 and the active layer 60 are not grown, more strictly, a portion exposed by growing at least the p-type second conduction-type cladding layer 70 and the active layer 60 and then removing a portion of the grown layers 70 and 60. Also, the p-type electrode 80 is electrically connected on the p-type second conduction-type cladding layer 70.
When a voltage is applied to the light-emitting device through the n-type electrode 50 and the p-type electrode 80, electrons are injected to the active layer 60 from the n-type first conduction-type cladding layer 40, and holes are injected to the active layer 60 from the p-type second conduction-type cladding layer 70. At this point, the electrons and holes injected into the active layer 60 recombine to generate light.
As described above, a sapphire substrate of substrates of various materials are generally used in the nitride light-emitting device. Although a sapphire substrate has an insulation characteristic and shows a high lattice mismatch of about 15-17% with respect to a GaN-based semiconductor material, the sapphire substrate is thermally stable and thus has little thermal damage at a range of about 1,000-1,200° C. during an epitaxial layer growth that uses metal oxide chemical vapor deposition (MOCVD). Also, the sapphire substrate is known as a high quality material of low defect concentration.
However, since the sapphire substrate in an insulator, a rear side contact is impossible during a device fabrication, so that there are lots of difficulties during a manufacturing process. Accordingly, it is general to perform a contact by performing dry-etching on a portion of a grown epitaxial layer, which is known in detail to the related art.
When dry-etching is performed on a related art nitride light-emitting device to etch a portion of an already grown epitaxial layer, a light-emitting area is reduced. When a chip size is reduced, an interval between a p-type electrode and an n-type electrode narrows, there is a high possibility that a short-circuit between the electrodes occurs. Also, there is a problem that a grown epitaxial layer is damaged during drying etching, and generates a defect, resulting in reduction of a light-emission efficiency. Consequently, these problems reduce brightness and reliability of a light-emitting device.
SUMMARY OF THE INVENTION
The present invention provides a light-emitting device and a manufacturing method thereof, capable of preventing a short-circuit between electrodes and improving a light-emission efficiency, brightness and reliability of the light-emitting device.
There is provided a light-emitting device including a first conduction-type cladding layer, an active layer, and a second conduction-type cladding layer stacked on a substrate, wherein portions of the substrate and the first conduction-type cladding layer are removed.
There is provided a semiconductor light-emitting device including a substrate, a first conduction-type cladding layer, an active layer, a second conduction-type cladding layer stacked, wherein a portion of the substrate is removed such that a lower surface of the first conduction-type cladding layer is exposed.
There is provided a method for manufacturing a light-emitting device, the method including: forming a first conduction-type cladding layer, an active layer, and a second conduction-type cladding layer on a substrate; lapping the substrate; etching at least the substrate to expose a portion of the first conduction-type cladding layer; and forming a first electrode on a lower surface of the exposed first conduction-type cladding layer and forming a second electrode on an upper surface of the second conduction-type cladding layer.
There is provided a method for manufacturing a light-emitting device, the method including: forming a first conduction-type cladding layer, an active layer, and a second conduction-type cladding layer on a substrate; etching at least a portion of the substrate from its lower portion to expose a portion of the first conduction-type cladding layer; and forming a first electrode on a lower surface of the exposed first conduction-type cladding layer and forming a second electrode on an upper surface of the second conduction-type cladding layer.
According to the present invention, a damage that can be caused on an already grown epitaxial layer can be reduced, and an area of an active layer is increased, so that a light-emission efficiency increases.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
FIG. 1 is a cross-sectional view of a nitride light-emitting device according to a related art;
FIGS. 2A to 2F are cross-sectional views sequentially explaining a process for manufacturing a light-emitting device according to the present invention
FIGS. 3-5 are views illustrating a texture pattern of a light-emitting device according to embodiments of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
FIGS. 2A to 2E are cross-sectional views sequentially explaining a process for manufacturing a light-emitting device according to the present invention.
First, in embodiments of the present invention, a nitride semiconductor using a compound such as GaN, AlN, and InN belonging to a group III and a group V can be independently used or used in combination for the light-emitting device. For example, referring to FIG. 2A, a light-emitting device includes a buffer layer 200, an un-doped GaN layer 300, a first conduction-type cladding layer 400, an active layer 500, and a second conduction-type cladding layer 600 sequentially stacked on a substrate 100 exemplified as a sapphire substrate.
In detail, the buffer layer 200 formed on the substrate 100 is intended for increasing a planarization of the substrate 100 to grow a high quality nitride. For example, a melt-back etching caused by a chemical reaction of the substrate 100 is prevented.
Also, the first conduction-type cladding layer 400 is grown on an upper surface of the un-doped GaN layer 300 which is a base layer for various semiconductor layers to be formed on the buffer layer 200.
The active layer 500 having a multiple quantum well (MQW) structure is a layer where holes flowing through the second electrode 900 and electrons flowing through the first electrode 800 recombine to generate light.
A second conduction-type cladding layer 600 is formed on the active layer 500.
Here, the first conduction-type cladding layer 400 may be an n-type layer, and the second conduction-type cladding layer 600 may be a p-type layer. Of course, conversely, the first conduction-type cladding layer 400 may be a p-type layer, and the second conduction-type cladding layer 600 may be an n-type layer.
After that, in the light-emitting device having the above-construction, a back side of the sapphire substrate 100 is lapped up to a thickness of 50 μm (that is, until the substrate has a thickness 50 μm) as is illustrated in FIG. 2B. Lapping the sapphire substrate 100 can prevent absorption of light emitted from the active layer 500. Furthermore, an etching process of the sapphire substrate 100 that is to be performed, can be performed fast and conveniently even more.
Subsequently, referring to FIG. 2C, a portion of the lapped sapphire substrate 100 is etched such that a portion of the first conduction-type cladding layer 400 is exposed. Here, the etching is performed using one of BCl3 and Cl2.
After that, referring to FIG. 2D, a lower surface of the lapped substrate 100 that is not etched is texture-processed using various patterns to form a texture processed portion 700.
The pattern is one of a quadrangular shape, a lens shape, a trapezoid, and so forth. This texture process can enhance a light-emission efficiency.
Referring to FIG. 2E, a first electrode 800 is formed on the exposed portion (lower surface) of the first conduction-type cladding layer 400. A second electrode 900 is formed on the second conduction-type layer 600. At this point, the second electrode 900 may be a transparent electrode formed of at least one material selected from the group consisting of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO), AGZnO(Al—Ga ZnO), IGZnO(In—Ga ZnO), and IrOx.
FIG. 2E explains a light-emitting device completely manufactured. The buffer layer 200, the un-doped GaN layer 300, the first conduction-cladding layer 400, the active layer 500, and the second conduction-type cladding layer 600 are sequentially formed on the lapped substrate 100. Also, with portions of the lapped substrate 100, the buffer layer 200, the un-doped GaN layer 300 etched, the electrode 800 is formed on a lower surface of the first conduction-type cladding layer 400. The electrode 900 is formed on an upper surface of the second conduction-type cladding layer 600. The texture processed portion 700 is formed on a lower surface of the lapped substrate 100.
Since a light-emitting device etches a portion of a backside of a sapphire substrate, a damage of a grown epitaxial layer can be prevented. Also, since an area of the active layer is increased, a light-emission efficiency is increased. Since the substrate is lapped, light absorption is prevented, so that a light-emission efficiency can be enhanced. Since a texture processed portion is provided in a lower surface of the substrate, a light-emission efficiency can be enhanced even more.
When a voltage is applied to the light-emitting device through the first electrode 800 and the second electrode 900, electrons are injected to the active layer 500 from the first conduction-type cladding layer 400, and holes are injected to the active layer 500 from the second conduction-type cladding layer 600. At this point, the electrons and holes injected into the active layer 500 recombine to generate light. Here, since the active layer 500 is not etched and thus has a wide light-emission area, a light-emission efficiency is improved, and the lapped substrate 100 and the texture processed portion 700 enhances a light-emission efficiency even more.
Though the above description of the present invention has been made for a p-n junction structure, as can be seen in FIG. 2f, the present invention can be applied to a nitride light-emitting device having an n-p-n junction structure where a third conduction-type cladding layer 700, which is an n-type cladding layer, is further formed on an upper surface of a second conduction-type cladding layer, which is a p-type cladding layer. Here, in the nitride light-emitting device having the n-p-n junction structure, each of a first cladding layer and a third cladding layer is an n-type cladding layer, and a p-type cladding layer is interposed between the first and third cladding layers. At this point, the first electrode is formed on the first cladding layer, which is an n-type cladding layer, and the second electrode is formed on the third cladding layer, which is an n-type cladding layer.
Also, the electrode does not directly contact the cladding layer but various type electrode layers may be further formed, which also comes within the scope of the present invention.
FIGS. 3 to 5 are cross-sectional views illustrating a texture shape of a light-emitting device according to the present invention. FIG. 3 illustrates a quadrangular texture processed portion 701, FIG. 4 illustrates a trapezoid texture processed portion 702, and FIG. 5 illustrates a circular texture processed portion 703. Of course, pluralities of layers are further formed on an upper surface of the lapped substrate 100 in FIGS. 3 to 5.
As described above, since a portion of a backside of a sapphire substrate is etched in a light-emitting device according to the present invention, damages to a grown epitaxial layer can be reduced. Also, since an area of the active layer is increased, a light-emission efficiency is increased.
Also, a short-circuit occurring between electrodes can be prevented even when a light-emitting device is small in size. Further, a backside of a substrate is texture-processed using various patterns, so that a light-emission efficiency is enhanced even more.
Meanwhile, the present invention can have various other embodiments within the scope to the spirit of the present invention is applied. For example, another layer can be interposed between an active layer and a cladding layer to reduce a lattice defect. Furthermore, another layer can further intervene between various layers described in the embodiments. Therefore, other layer stacked on one layer in the embodiments can be directly staked as described, and another layer can further intervene in order to enhance a light-emission efficiency of a light-emitting device.

## Claims

1. A semiconductor light-emitting device, comprising:
a light emitting structure including a first conduction-type cladding layer, a second conduction-type cladding layer, and an active layer between the first conduction-type cladding layer and second conduction-type cladding layer;
a non-conductive substrate on a first portion of the light emitting structure and having a horizontal surface area smaller than a horizontal surface area of the active layer;
a first electrode electrically connected to the first conduction-type cladding layer on a second portion of the light emitting structure and having a horizontal surface area smaller than a horizontal surface area of the second portion; and
a second electrode electrically connected to the second conduction-type cladding layer,
wherein the horizontal surface area of the second portion is smaller than a horizontal surface area of the first portion, and
wherein the horizontal surface area of the first electrode is in direct contact with the first conduction-type cladding layer and has a horizontal surface area smaller than the horizontal surface area of the second portion.

2. The semiconductor light-emitting device according to claim 1, wherein the horizontal surface areas of the first and second portions do not overlap.

3. The semiconductor light-emitting device according to claim 1, wherein the non-conductive substrate is not in contact with the first electrode.

4. The semiconductor light-emitting device according to claim 1, further comprising:
a buffer layer between the non-conductive substrate and the light emitting structure, the buffer layer having a horizontal surface area smaller than the horizontal surface area of the active layer.

5. The semiconductor light-emitting device according to claim 4, further comprising:
an un-doped GaN layer between the buffer layer and the light emitting structure, the un-doped GaN layer having a horizontal surface area smaller than the horizontal surface area of the active layer.

6. The semiconductor light-emitting device according to claim 1, wherein the non-conductive substrate is a sapphire substrate.

7. The semiconductor light-emitting device according to claim 1,
wherein the non-conductive substrate has a first surface facing the light emitting structure and a second surface opposing the first surface, and
wherein the second surface includes a texture processed portion.

8. The semiconductor light-emitting device according to claim 1, wherein the texture processed portion includes a pattern including one of a quadrangular shape, a lens shape, and a trapezoid shape.

9. The semiconductor light-emitting device according to claim 1, further comprising:
a third conduction-type cladding layer between the second conduction-type cladding layer and the second electrode, wherein the first conduction-type cladding layer is an n-type cladding layer and the second conduction-type cladding layer is an p-type cladding layer and the third conduction-type cladding layer is an n-type cladding layer.

10. A method for manufacturing a light-emitting device, the method comprising:
forming a light emitting structure including a first conduction-type cladding layer, a second conduction-type cladding layer, and an active layer between the first conduction-type cladding layer and second conduction-type cladding layer on a non-conductive substrate;
lapping the non-conductive substrate;
etching a portion of the non-conductive substrate so that the non-conductive substrate has a horizontal surface area smaller than a horizontal surface area of the active layer;
forming a first electrode electrically connected to the first conduction-type cladding layer on a corresponding etched portion of the light emitting structure, wherein first electrode has a horizontal surface area smaller than a horizontal surface area of the etched portion; and
forming a second electrode electrically connected to the second conduction-type cladding layer,
wherein the horizontal surface area of the etched portion is smaller than a horizontal surface area of a corresponding unetched portion of the light emitting structure, and
wherein the horizontal surface area of the first electrode is in direct contact with the first conduction-type cladding layer and has a horizontal surface area smaller than the horizontal surface area of the etched portion.

11. The method according to claim 10, wherein the non-conductive substrate is not in contact with the first electrode.

12. The method according to claim 10, further comprising:
forming a buffer layer between the non-conductive substrate and the light emitting structure, the buffer layer having a horizontal surface area smaller than the horizontal surface area of the active layer.

13. The method according to claim 12, further comprising:
forming an un-doped GaN layer between the buffer layer and the light emitting structure, the un-doped GaN layer having a horizontal surface area smaller than the horizontal surface area of the active layer.

14. The method according to claim 10, wherein the non-conductive substrate is a sapphire substrate.

15. The method according to claim 10,
wherein the non-conductive substrate has a first surface facing the light emitting structure and a second surface opposing the first surface, and
wherein the second surface includes a texture processed portion.

16. The method according to claim 10, wherein the texture processed portion includes a pattern including one of a quadrangular shape, a lens shape, and a trapezoid shape.

17. The method according to claim 10, further comprising:
forming a third conduction-type cladding layer between the second conduction-type cladding layer and the second electrode, wherein the first conduction-type cladding layer is an n-type cladding layer and the second conduction-type cladding layer is an p-type cladding layer and the third conduction-type cladding layer is an n-type cladding layer.