CN109148663B

CN109148663B - Light-emitting diode and method of making the same

Info

Publication number: CN109148663B
Application number: CN201810987785.4A
Authority: CN
Inventors: 吴琼; 李威平
Original assignee: Fujian Prima Optoelectronics Co Ltd
Current assignee: Fujian Prima Optoelectronics Co Ltd
Priority date: 2018-08-28
Filing date: 2018-08-28
Publication date: 2020-05-12
Anticipated expiration: 2038-08-28
Also published as: CN109148663A

Abstract

The present invention relates to a light emitting diode and a manufacturing method thereof. It includes a substrate, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer sequentially arranged from bottom to top, and the area of the active layer and the P-type semiconductor layer is smaller than that of the N-type semiconductor layer to expose part of the N-type semiconductor layer. The N-type pad electrode above the N-type semiconductor layer and electrically connected to the N-type semiconductor layer, the P-type pad electrode located above the P-type semiconductor layer and electrically connected to the P-type semiconductor layer, and the N-type pad electrode located above the P-type semiconductor layer and electrically connected to the P-type semiconductor layer. The finger electrodes extended from the pad electrode and the P-type pad electrode, and the passivation layer located above the N-type semiconductor layer and above the P-type semiconductor layer and exposing the N-type pad electrode and the P-type pad electrode; the N-type solder The pad electrode, the P-type pad electrode, and the finger electrode all include an ohmic contact layer, a lower reflective layer, a stress relaxation layer, a conductive metal layer, and an upper reflective layer that are sequentially arranged from bottom to top. In the present invention, the light totally reflected by the passivation layer is prevented from being absorbed by the metal electrode again through the upper reflective layer, thereby improving the external light extraction efficiency.

Description

Light emitting diode and method for manufacturing the same

Technical Field

The present invention relates to a light emitting diode and a method for manufacturing the same, and more particularly, to a light emitting diode including a reflective layer for improving light extraction efficiency by reducing light absorption of a pad electrode and a finger electrode, and a method for manufacturing the same.

Background

When the semiconductor light emitting element is connected to a forward voltage, holes in the P-type semiconductor layer are recombined with electrons in the N-type semiconductor layer, and light having a wavelength with a corresponding band gap width is emitted. Gallium nitride series semiconductor (Al)_xIn_yGa_1-x-yN, x is 0 to 1, y is 0 to 1, and x + y is 0 to 1) can emit light of various wavelengths by changing the composition ratio of three elements of Al, In and Ga, and thus the material is a light-emitting element material which is favored.

The P-type semiconductor layer constituting the gallium nitride-based semiconductor light-emitting device has a problem of an excessively large resistance due to a small carrier mobility. When a current is injected into the P-type gallium nitride semiconductor layer having a large resistance, electric charges are not diffused throughout the semiconductor layer but are concentrated in a path having a small resistance, and thus, a phenomenon of uneven light emission due to current crowding occurs. This phenomenon is one of the major problems of decreasing the luminance of the element.

Therefore, in order to diffuse the current to the entire P-type semiconductor layer, a transparent electrode layer is formed on the P-type semiconductor layer. Another way to spread the current throughout the P-type semiconductor layer is to form a finger electrode extending from the pad electrode to prevent the current from concentrating around the bond site connected to the wire.

Since both the pad electrode and the finger electrode are made of a highly conductive metal, and the electrode made of a metal material generally used is relatively thick, one of the factors that light absorption causes a decrease in light extraction efficiency is caused.

Disclosure of Invention

The invention aims to provide a light emitting diode and a manufacturing method thereof, which prevent light totally reflected by a passivation layer from being absorbed by a metal electrode through an upper reflection layer, thereby improving external light extraction efficiency.

In order to achieve the purpose, the technical scheme of the invention is as follows: a light emitting diode comprises a substrate, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially arranged from bottom to top, wherein the areas of the active layer and the P-type semiconductor layer are smaller than that of the N-type semiconductor layer so as to expose part of the N-type semiconductor layer; the N-type pad electrode, the P-type pad electrode and the finger electrode respectively comprise an ohmic contact layer, a lower reflecting layer, a stress relieving layer, a conductive metal layer and an upper reflecting layer which are sequentially arranged from bottom to top.

In an embodiment of the present invention, the ohmic contact layer is formed of chromium, the lower reflective layer is formed of aluminum or silver, the stress relaxation layer is formed of nickel, titanium, or chromium, and the conductive metal layer is formed of platinum or gold.

In an embodiment of the present invention, the upper reflective layer is formed of aluminum, silver, or DBR.

In an embodiment of the invention, a transparent electrode layer is further disposed between the P-type semiconductor layer and the P-type pad electrode.

In an embodiment of the invention, a current blocking layer is further disposed in a partial region between the P-type semiconductor layer and the transparent electrode layer, and the current blocking layer is located right below the P-type pad electrode.

The invention also provides a manufacturing method based on the light-emitting diode, which comprises the following steps of firstly, forming an ohmic contact layer on the P-type semiconductor layer; then, forming a lower reflection layer on the ohmic contact layer; then, forming a stress relaxation layer on the lower reflection layer; then, forming a conductive metal layer on the stress relaxation layer, and finally forming an upper reflection layer on the conductive metal layer; in the step of forming the upper reflective layer, the upper reflective layer is formed on a partial region of the conductive metal layer of the N-type pad electrode and the P-type pad electrode and on the entire conductive metal layer of the finger electrode.

In an embodiment of the present invention, in the process of forming the upper reflective layer, the upper reflective layer is formed on the conductive metal layers of the N-type and P-type pad electrodes and the finger electrode, and the upper reflective layer is removed from a partial region of the N-type and P-type pad electrodes.

In an embodiment of the present invention, a process of forming a current blocking layer on a partial region of the P-type semiconductor layer and a process of forming a transparent conductive layer on the current blocking layer and the P-type semiconductor layer are further included, and a P-type pad electrode is formed right above the region where the current blocking layer is formed.

Compared with the prior art, the invention has the following beneficial effects: the N-type pad electrode, the P-type pad electrode and the finger electrode comprise an ohmic contact layer, a lower reflecting layer, a stress relieving layer, a conductive metal layer and an upper reflecting layer. The ohmic contact layer enables the electrode structure to form ohmic contact with the P-type semiconductor layer or the transparent conducting layer, so that power is supplied to the P-type semiconductor layer more effectively. The lower reflective layer prevents light emitted from the active layer from being absorbed by the conductive metal layers of the N-type pad electrode, the P-type pad electrode, and the finger electrode. The stress relaxation layer is bonded to the lower reflection layer and the conductive metal layer. The conductive metal layer formed on the stress relaxation layer is used for electrifying the bonding wire. The upper reflective layer prevents light reflected by a passivation layer formed on the light emitting diode structure from being absorbed by the conductive metal layer. Therefore, the light emitting diode provided by the embodiment of the invention is easy to diffuse current, and the light emitting efficiency of the light emitting diode can be improved due to less light absorption.

Drawings

Fig. 1 is a plan view of a light emitting diode according to an embodiment of the invention.

Fig. 2 is a cross-sectional view of the led shown in fig. 1 cut along line a-a' and shown.

Fig. 3 is a cross-sectional view of the led shown in fig. 1 cut away along line B-B' to show the led.

Fig. 4 is a cross-sectional view of an electrode layer of a light emitting diode according to an embodiment of the invention.

In the figure, the position of the upper end of the main shaft,

10: substrate 20: luminescent layer

21: n-type semiconductor layer 23: active layer

25: p-type semiconductor layer 30: electrode layer

31: p-type pad electrode 33: p-type finger electrode

35: n-type pad electrode 37: n-type finger electrode

40. 40a, 40 b: upper reflective layer 51: transparent electrode layer

53: current blocking layer 60: passivation layer

71: ohmic contact layer 73: lower reflective layer

75: stress relaxation layer 77: a conductive metal layer.

Detailed Description

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is not intended to limit the invention to the particular forms shown, but, on the contrary, the intention is to cover all modifications, equivalents, alternatives, and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

When an element such as a layer, a section, or a substrate is referred to as being present "on" another constituent element, it is to be understood that the element may be present directly on the other element or may be present as an intermediate element between the element and the other element.

Although the terms of level 1 and level 2 may be used to describe various elements, components, sections, layers and/or regions, it should be understood that these elements, components, sections, layers and/or regions are not limited to these terms.

Preferred embodiments of the present invention will be described in detail with reference to the following drawings. In the following drawings, the same reference numerals are used for the same components, and the description of the same components will not be repeated.

The invention provides a light-emitting diode, which comprises a substrate, an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially arranged from bottom to top, wherein the areas of the active layer and the P-type semiconductor layer are smaller than that of the N-type semiconductor layer so as to expose part of the N-type semiconductor layer; the N-type pad electrode, the P-type pad electrode and the finger electrode respectively comprise an ohmic contact layer, a lower reflecting layer, a stress relieving layer, a conductive metal layer and an upper reflecting layer which are sequentially arranged from bottom to top.

The ohmic contact layer is formed of chromium, the lower reflection layer is formed of aluminum or silver, the stress relaxation layer is formed of nickel, titanium or chromium, and the conductive metal layer is formed of platinum or gold. The upper reflective layer is formed of aluminum, silver, or DBR.

And a transparent electrode layer is also arranged between the P-type semiconductor layer and the P-type pad electrode.

And a current blocking layer is also arranged in a partial area between the P-type semiconductor layer and the transparent electrode layer and is positioned right below the P-type welding disc electrode.

In the above method for manufacturing a light emitting diode, in the process of forming the upper reflective layer, the upper reflective layer is formed on the conductive metal layers of the N-type and P-type pad electrodes and the finger electrode, and the upper reflective layer on the partial regions of the N-type and P-type pad electrodes is removed.

The method for manufacturing a light emitting diode further includes a step of forming a current blocking layer on a partial region of the P-type semiconductor layer, and a step of forming a transparent conductive layer on the current blocking layer and the P-type semiconductor layer, and forming a P-type pad electrode directly above the region where the current blocking layer is formed.

The following are specific examples of the present invention.

Referring to fig. 1, a light emitting diode according to an embodiment of the present invention includes a light emitting layer (20) including an N-type semiconductor layer, an active layer, and a P-type semiconductor, a P-type pad electrode (31) electrically connected to the P-type semiconductor, a P-type finger electrode (33) extending from the P-type pad electrode, an N-type pad electrode (35) electrically connected to the N-type semiconductor layer, and an N-type finger electrode (37) extending from the N-type pad electrode (35). The P-type finger electrode (33) extends from the P-type pad electrode (31) to the N-type pad electrode (35) on the P-type semiconductor layer.

The N-type finger electrode (37) is formed on the N-type semiconductor layer, and extends from the N-type pad electrode (35) to surround the P-type finger electrode (33). It is thus possible to efficiently conduct the current to the entire light-emitting layer (20).

Fig. 2 is a cross-sectional view of the led shown in fig. 1 cut along line a-a' and shown. Fig. 3 is a cross-sectional view of the led shown in fig. 1 cut away along line B-B' to show the led.

Referring to fig. 2, a light emitting diode according to an embodiment of the present invention includes a substrate (10), a light emitting layer (20) formed on the substrate (10) and including an N-type semiconductor layer (21), an active layer (23), and a P-type semiconductor layer (25), an electrode layer (30) including a P-type pad electrode (31) formed on the light emitting layer (20) and electrically connected to the P-type semiconductor layer (25), a P-type finger electrode (33) extending from the P-type pad electrode (31), an N-type pad electrode (35) electrically connected to the N-type semiconductor layer, an N-type finger electrode (37) extending from the N-type pad electrode (35), and a passivation layer (60).

Any substance that is known to be usable as a GaN LED substrate can be used as the substrate (10) without limitation. The semiconductor material generally used for growing gallium nitride may be any one of SiC, Si, GaN, ZnO, GaAs, GaP, LiAl2O3, BN and AlN, but is not limited thereto. The substrate (10) may have a concave-convex pattern so as to reflect light formed and emitted from the active layer (23) by growing a high-quality gallium nitride light emitting layer (20), thereby improving light extraction efficiency.

The gallium nitride light-emitting structure is formed on the substrate (10). First, an active layer (23) is formed on an N-type semiconductor layer (21). A P-type semiconductor layer (25) is further formed on the active layer (23). The P-type semiconductor layer (25) and the active layer (23) are partially etched to expose the N-type semiconductor layer (21).

The light-emitting layer (20) may be Al_xIn_yGa_1-x-yN (x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and x + y is more than or equal to 0 and less than or equal to 1). The N-type semiconductor layer (21) may include an N-type dopant of a type such as silicon (Si), germanium (Ge), tin (Sn), and the P-type semiconductor may include a P-type dopant of a type such as magnesium (Mg), zinc (Zn), or cadmium (Cd). The active layer (23) may have a single quantum well structure or a multiple quantum well structure. The active layer (23) of the multiple quantum well structure may be a structure in which semiconductor layers having a large band gap and semiconductor layers having a small band gap are alternately stacked.

The N-type semiconductor layer (21), the active layer (23), and the P-type semiconductor layer (25) may be formed by Chemical Vapor Deposition (CVD), Hydride Vapor Phase Epitaxy (HVPE), Atomic layer deposition (Atomic layer deposition), or other well-known growth methods.

A transparent conductive layer (51) can be selectively formed on the P-type semiconductor layer (25). The transparent conductive layer (51) can be formed as a very thin Ni/Au thin film or a conductive metal oxide thin film. The transparent conductive layer (51) can diffuse a current to the P-type semiconductor layer (25) having a low hole density.

When the transparent conductive layer (51) is formed, a current blocking layer (53) can be formed in a partial region on the P-type semiconductor layer (25). The current blocking layer (53) is formed on the P-type pad electrode (31) and prevents current from flowing from below the P-type pad electrode to the active region. Then, the current flows out from the P-type pad electrode (31) in a bent manner, and the light extraction efficiency is improved.

The P-type pad electrode (31) is formed on the P-type semiconductor layer (25) or the transparent conductive layer (51). An N-type pad electrode (35) is formed on the N-type semiconductor layer (21) exposed from the active layer (23) and the P-type semiconductor layer (25).

The P-type finger electrode (33) is formed by extending the P-type pad electrode (31) toward the N-type pad electrode (35). The N-type finger electrode (37) is extended from the N-type pad electrode (31) and formed to surround the P-type finger electrode (33). The electrode layer (30) including the P-type pad electrode (31), the N-type pad electrode (35), the P-type finger electrode (33), and the N-type finger electrode (37) may have various forms in order to effectively diffuse the current.

The electrode layer (30) can be formed by a known deposition method such as electron beam evaporation, high-frequency induction evaporation, magnetron sputtering, or the like.

An upper reflective layer (40) is formed on the electrode layer (30). The upper reflective layer (40, 40a or 40b) may be aluminum (Al), silver (Ag) or dbr (distributed Bragg reflector). The upper reflective layer (40) prevents light totally reflected by the passivation layer (60) from being absorbed by the conductive metal layer, thereby improving light extraction efficiency.

When the upper reflective layer (40) is a DBR, the upper reflective layer (40) may have a structure in which insulating films having different refractive indices are alternately stacked. The low refractive index layer may be silicon oxide or aluminum oxide (Al)₂O₃) The film, high refractive index layer may be silicon nitride or titanium oxide (TiO)₂) A film.

The upper reflection layer (40) etches away a part of the region on the P-type pad electrode (31) and the N-type pad electrode (35) to form an opening for wire bonding.

A passivation layer (60) is formed to cover the light-emitting layer (20) and the electrode layer (30). The passivation layer (60) is formed to prevent a decrease in light emitting efficiency due to physical, chemical, and electrical damage. The passivation layer (60) may contain a fluorescent substance for forming a white light emitting diode. The fluorescent substance may be a yellow fluorescent substance yag (yttrium aluminum garnet).

Light emitted from the light emitting structure may be reflected by the passivation layer (60). The reflected light can be reflected again by the upper reflection layer (40) and emitted out, thereby improving the external light extraction efficiency of the light emitting diode.

Referring to fig. 4, the electrode layer (30) may have a multi-layer structure including an ohmic contact layer (71) formed on the P-type semiconductor layer or the transparent electrode layer, a lower reflective layer (73) formed on the ohmic contact layer (71), a stress relaxation layer (75) formed on the lower reflective layer (73), and a conductive metal layer (77).

The ohmic contact layer (71) may include chromium (Cr), and is formed to realize ohmic contact between the P-type semiconductor layer or the transparent conductive layer and the electrode layer (30).

The lower reflection layer (73) contains Aluminum (AL) or silver (Ag), and reflects light emitted from the active region, thereby preventing the light from being absorbed by the conductive metal layer (77).

The stress relaxation layer (75) includes nickel (Ni), titanium (Ti), or chromium (Cr), so that ohmic contact between the lower reflection layer (73) and the conductive metal layer (77) can be achieved.

The conductive metal layer (77) may include platinum (Pt) or gold (Au).

The upper reflective layer (40) is formed on the conductive metal layer (77). The upper reflection layer (40) can reflect the light totally reflected by the passivation layer (60) again, thereby improving the external light extraction efficiency.

The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.

Claims

1. A light-emitting diode, characterized in that it comprises a substrate, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer sequentially arranged from bottom to top, and the area of the active layer and the P-type semiconductor layer is smaller than that of the N-type semiconductor layer, so as to A part of the N-type semiconductor layer is exposed, and an N-type pad electrode located above the N-type semiconductor layer and electrically connected to the N-type semiconductor layer is located above the P-type semiconductor layer and electrically connected to the P-type semiconductor layer. The P-type pad electrode, the finger-shaped electrode extending from the N-type pad electrode and the P-type pad electrode, are located above the N-type semiconductor layer and above the P-type semiconductor layer and expose the N-type pad electrode and the P-type pad The passivation layer of the electrode; the N-type pad electrode, P-type pad electrode, and finger-shaped electrode all include an ohmic contact layer, a lower reflection layer, a stress relaxation layer, a conductive metal layer, and an upper reflection layer arranged in order from bottom to top Floor.

2 . The light emitting diode according to claim 1 , wherein the ohmic contact layer is formed of chromium, the lower reflective layer is formed of aluminum or silver, and the stress relaxation layer is formed of nickel, titanium or chromium, 2 . The conductive metal layer is formed of platinum or gold.

3. The light emitting diode of claim 1, wherein the upper reflective layer is formed of aluminum, silver or DBR.

4 . The light emitting diode according to claim 1 , wherein a transparent electrode layer is further provided between the P-type semiconductor layer and the P-type pad electrode. 5 .

5 . The light-emitting diode according to claim 4 , wherein a current blocking layer is further provided in a partial area between the P-type semiconductor layer and the transparent electrode layer, and the current blocking layer is located on the P-type pad electrode. 6 . directly below.

6. A method for manufacturing a light-emitting diode according to any one of claims 1 to 5, wherein, first, an ohmic contact layer is formed on the P-type semiconductor layer; then, an ohmic contact layer is formed on the ohmic contact layer a lower reflective layer; then, a stress relaxation layer is formed on the lower reflective layer; further, a conductive metal layer is formed on the stress relaxation layer, and finally an upper reflective layer is formed on the conductive metal layer; In the process of the upper reflective layer, the upper reflective layer is formed on the partial area of the conductive metal layer of the N-type pad electrode and the P-type pad electrode and the entire surface of the conductive metal layer of the finger electrode. process.

7 . The manufacturing method according to claim 6 , wherein the ohmic contact layer is formed of chromium, the lower reflective layer is formed of aluminum or silver, and the stress relaxation layer is formed of nickel, titanium or chromium, 7 . The conductive metal layer is formed of platinum or gold.

8 . The manufacturing method according to claim 6 , wherein in the process of forming the upper reflective layer, a conductive metal layer of the N-type pad electrode, the P-type pad electrode and the finger electrode is formed. 9 . The upper reflective layer is formed thereon, and the upper reflective layer on the partial regions of the N-type pad electrode and the P-type pad electrode is removed.

9. The method of claim 6, wherein the upper reflective layer is formed of aluminum, silver or DBR.

10. The manufacturing method according to claim 6, further comprising a process of forming a current blocking layer on a partial region of the P-type semiconductor layer, and a process of forming a current blocking layer on the current blocking layer and the P-type semiconductor layer. The process of forming a transparent conductive layer on the semiconductor layer, and forming a P-type pad electrode just above the region where the current blocking layer is formed.