TWI469386B - Light emitting diode and method for making the same - Google Patents

Description

Light-emitting diode and manufacturing method thereof

The present invention relates to a light emitting diode, and more particularly to a light emitting diode capable of improving luminous efficiency and a method of fabricating the same.

A Light Emitting Diode (LED) is a semiconductor component that converts current into light of a specific wavelength range. The light-emitting diode is widely used in the field of illumination because of its high brightness, low operating voltage, low power consumption, easy matching with integrated circuits, simple driving, and long life.

The LED typically includes a p-type semiconductor layer, an active layer, and an n-type semiconductor layer. Applying a voltage across the LED, holes and electrons will recombine in the active layer, radiating photons. One of the problems faced by LEDs in the application process is their light extraction efficiency. Since the photons are generated by the passage of current in the active layer, the light extraction efficiency of the LED has a great relationship with the uniformity of current distribution on the surface of the LED device. One method for improving the light-emitting efficiency of the LED is to epitaxially grow a current spreading layer under the electrode, and use the current spreading layer to laterally expand the injection current, so that the current is evenly distributed on the surface of the device, thereby improving the light-emitting efficiency. One disadvantage of this method is that the thickness of the current spreading layer is proportional to the area of the LED device. The larger the area of the LED device, the thicker the current spreading layer is. Since the existing epitaxial growth technique is difficult to obtain a current spreading layer having a large thickness and a high doping concentration, the lateral current spreading capability to the current spreading layer is limited.

In view of this, it is necessary to provide a light-emitting diode having higher luminous efficiency.

A light emitting diode comprising a heat conductive substrate and a semiconductor layer, a transparent electrode layer and an electrode contact pad formed on the surface of the heat conductive substrate in sequence. The semiconductor layer includes a p-type semiconductor layer, an active layer, and an n-type semiconductor layer which are sequentially stacked on a thermally conductive substrate. The transparent electrode layer and the electrode contact pad are disposed on the surface of the n-type semiconductor layer. A plurality of etching holes are disposed on a surface of the n-type semiconductor layer opposite to the active layer, and a distribution density of the etching holes is highest at a position closest to the electrode contact pads, and a distribution density of the etching holes is gradually smaller in a direction away from the electrode contact pads. The size of the etched holes is also gradually reduced. A current blocking layer is disposed on a surface of the p-type semiconductor layer opposite to the active layer, and the pattern of the current blocking layer is complementary to the pattern of the etched holes.

A method for manufacturing a light-emitting diode, the steps of which are:

Providing a sapphire substrate;

Forming an n-type semiconductor layer, an active layer, and a p-type semiconductor layer sequentially on the sapphire substrate;

Etching a pattern required for the current blocking layer on the surface of the p-type semiconductor layer, and then filling the pattern with an electrically insulating medium to form a current blocking layer;

Depositing a reflective layer on the surface of the p-type semiconductor layer;

Bonding the p-type semiconductor layer to the thermally conductive substrate to remove the sapphire substrate;

Etching the surface of the n-type semiconductor layer to form a desired etched hole, the pattern of the etched hole being complementary to the pattern of the current blocking layer;

Forming a transparent electrode layer on the surface of the n-type semiconductor layer;

An electrode contact pad is formed on the surface of the transparent electrode layer.

Compared with the prior art, the present invention provides an etch hole having a lower distribution density and a smaller size at a place away from the electrode contact pad by providing an etch hole having a higher distribution density and a larger size near the electrode contact pad. , to drive the current to flow away from the current contact pad, so that the current distribution is uniform. The reason is that it is close to the electrode contact pad, because the distribution density of the etched hole is high, that is, the resistance value is large, and the driving current is diffused toward a place where the etching hole density is small, that is, the resistance value is small. Thereby the current is spread to the surroundings along the current contact pads. At the same time, in order to make a current flow through the active layer facing the etched portion, a current blocking layer is formed on the surface of the p-type semiconductor layer in a complementary relationship with the etched hole pattern, so that the current spreads to both sides due to the action of the current blocking layer. That is, the current is evenly distributed on the active layer, thereby improving the luminous efficiency of the entire device.

The invention is further illustrated by the following specific examples.

Referring to FIG. 1, a light emitting diode according to an embodiment of the present invention includes a heat conductive substrate 11 and a p-type semiconductor layer 121, an active layer 122, and an n-type semiconductor layer 123 which are sequentially formed on the surface of the heat conductive substrate 11. At the same time, the light emitting diode further includes a transparent electrode layer 13 and an electrode contact pad 14.

The heat conductive substrate 11 is made of a material having high thermal conductivity, and may be a substrate made of a metal material such as copper, aluminum, nickel, silver, gold or the like, or an alloy formed of any two or more metals, or a thermal conductivity. A good ceramic substrate such as a tantalum substrate or a tantalum substrate. In the present embodiment, the thermally conductive substrate 11 is a metallic nickel layer having high thermal conductivity.

The p-type semiconductor layer 121, the active layer 122, and the n-type semiconductor layer 123 are sequentially laminated on the thermally conductive substrate 11. The material for fabricating the semiconductor layer includes gallium nitride, aluminum gallium nitride, and indium gallium nitride. In this embodiment, the semiconductor layer is made of a gallium nitride material.

The transparent electrode layer 13 is provided on the surface of the n-type semiconductor layer 123, and the transparent electrode layer 13 is made of an ITO (Indium Tin Oxide) transparent conductive film. The use of the transparent electrode layer 13 does not block the light emitted from the light-emitting diode, thereby improving the light-emitting efficiency of the light-emitting diode. In the present embodiment, the shape of the transparent electrode layer 13 coincides with the surface shape of the n-type semiconductor layer 123.

The electrode contact pad 14 is disposed on the surface of the transparent electrode layer 13 as a connection region between the light emitting diode and the external power source. The n-type contact pad 14 is made of a metal material such as silver, gold, copper or aluminum. In the present embodiment, the electrode contact pad 14 is disposed at a center position of the light emitting diode.

A plurality of etching holes 124 are provided on the surface of the n-type semiconductor layer 123 opposite to the active layer 122, as shown in FIG. The etched holes 124 have the highest density of distribution closest to the electrode contact pads 14. Along the direction away from the electrode contact pads 14, the distribution density and size of the etched holes 124 gradually become smaller, forming a pattern having a gradual distribution density and size. In the present embodiment, the etch holes 124 are distributed around the electrode contact pads 14, and the etch holes 124 enclose a plurality of annular patterns of different radii. Each annular pattern consists of etched holes 124 of the same size and shape. The etched holes 124 of this embodiment are circular in shape, and the circular etched holes 124 have the largest diameter near the electrode contact pads 14. In the direction away from the electrode contact pad 14, the diameter of the etched hole 124 gradually becomes smaller. Moreover, in the direction away from the electrode contact pad 14, the distance between the annular patterns is also larger, and the distance between the etching holes 124 constituting the same annular pattern is also larger.

The effect of providing a plurality of etching holes 124 on the surface of the n-type semiconductor layer 123 is that since the etching holes 124 have a large distribution density near the electrode contact pads 14, that is, the resistance value is large, and the distribution density is small away from the electrode contact pads 14. That is, the resistance value is small, so that the current flows from the place where the density of the etched holes 124 is distributed to the place where the distribution density of the etched holes 124 is small, even if the current flows in a direction away from the electrode contact pad 14, the current distribution is uniform, and the light emission is improved. The luminous efficiency of the polar body.

The pattern of the etched holes 124 constituting the annular pattern may also be an equilateral triangle, a square, a regular hexagon, a regular polygon, or other regular or irregular shape, as needed. The size of the etched holes 124 gradually decreases in a direction away from the electrode contact pads 14.

The etching hole 124 has a depth of about 1/3 to 2/3 of the thickness of the n-type semiconductor layer 123. The purpose is to prevent the etched holes 124 from being too close to the active layer 122. If the etched holes 124 are too close to the active layer 122, the active layer 122 at the corresponding location of the etched holes 124 will have no current to pass, reducing the luminous efficiency to the device. Therefore, a certain spacing is provided between the etched holes 124 and the active layer 122 to disperse the current. Taking the n-type semiconductor layer 123 having a thickness of 3 μm as an example, the thickness of the etching hole 124 is preferably between 1 μm and 2 μm, that is, the depth of the etching hole is preferably between 1 μm and 2 μm.

The active layer 122 is disposed between the p-type semiconductor layer 121 and the n-type semiconductor layer 123. When a voltage is applied between the p-type semiconductor layer 121 and the n-type semiconductor layer 123, the active layer 122 will have an electric current, that is, a p-type The holes in the semiconductor layer 121 are recombined with the electrons in the n-type semiconductor layer 123, thereby radiating photons.

The p-type semiconductor layer 121 is between the active layer 122 and the thermally conductive substrate 11. A surface of the p-type semiconductor layer 121 in contact with the thermally conductive substrate 11 is provided with a current blocking layer 125 composed of an insulating material. The material of the current blocking layer 125 in this embodiment is a ceria material. The pattern of the current blocking layer 125 is complementary to the pattern formed by the etched holes 124, that is, where the etched holes 124 are provided on the surface of the n-type semiconductor layer 123, no current blocking layer is provided at the corresponding position of the p-type semiconductor layer 121. 125; Where the etched holes 124 are not provided, a current blocking layer 125 is disposed at a corresponding position of the p-type semiconductor layer 121.

The function of the current blocking layer 125 is to allow current to pass through the portion of the active layer 122 that is blocked by the etched holes 124. If there is no current blocking layer 125, when the entire light emitting diode is energized, current will flow directly from the unetched n-type semiconductor layer 123 to the corresponding active layer 122 below, and then reach the p-type semiconductor layer, so that The active layer 122 corresponding to the adjacent etched holes 124 has less current. If a current blocking layer 125 having an insulating property is disposed at a corresponding position of the unetched n-type semiconductor layer 123, the current will be diffused to the both sides by the current blocking layer 125, so that the active layer corresponding to the side etching hole 124 is provided. 122 also has a current passing through, so that the current is evenly distributed throughout the active layer 122, improving the luminous efficiency of the device.

The current blocking layer 125 has a thickness of about 1/3 to 2/3 of the thickness of the p-type semiconductor layer 121. Similar to the etched holes 124 in the n-type semiconductor layer 123, the current blocking layer 125 cannot be too close to the active layer 122 because a certain spacing needs to be reserved between the current blocking layer 125 and the active layer 122 to evenly distribute the current. Taking the p-type semiconductor layer 121 having a thickness of 0.3 μm as an example, the thickness of the current blocking layer 125 is preferably between 0.1 μm and 0.2 μm.

In the light-emitting diode of the present embodiment, the pattern of the etching holes 124 provided on the n-type semiconductor layer 123 is complementary to the pattern of the current blocking layer 125 provided on the surface of the p-type semiconductor layer 123. Therefore, precise positioning is required in the fabrication process of the light-emitting diode. A positioning method provides a positioning hole at any position of the light emitting diode, the positioning hole functioning to determine the position of the pattern of the current blocking layer 125, and then etching the hole 124 when the etching hole 124 is formed on the n-type semiconductor layer 123 The pattern maintains a complementary relationship with the pattern of current blocking layer 125. The positioning hole extends from the p-type semiconductor layer 121 to the n-type semiconductor layer 123. In fact, the positioning method is not limited to the positioning holes, and other positioning methods may be used as long as the pattern formed by the etching holes 124 is complementary to the pattern of the current blocking layer 125.

A reflective layer 15 having a high reflectivity may be disposed between the p-type semiconductor layer 121 and the thermally conductive substrate 11 as needed. The reflective layer 15 may be a Bragg reflection layer, or may be made of silver, nickel, aluminum, or copper. A metallic specular reflection layer made of a metal such as gold. The purpose of the reflective layer 15 is to reflect the light emitted from the active layer 122 toward the p-type semiconductor layer 121 and emit it from the surface of the n-type semiconductor layer 123, thereby improving the light-emitting efficiency of the entire light-emitting diode.

Next, a method of fabricating the above-described light-emitting diode will be described.

3A-3I illustrate a method for fabricating a light-emitting diode according to the embodiment, and the steps thereof include:

Referring to Figure 3A, a sapphire substrate 16 is first provided;

Referring to FIG. 3B, an n-type GaN layer 123, an active layer 122, and a p-type GaN layer 121 are sequentially formed on the sapphire substrate 16 by metal organic chemical vapor deposition (MOCVD).

Referring to FIG. 3C, a pattern recess of the current blocking layer 125 is etched on the surface of the p-type GaN layer 121 using an inductive couple plasma (ICP) etching system. The etching method may be that a photoresist layer is first coated on the surface of the p-type GaN layer 121, and then the corresponding photoresist layer is removed by exposure and development, and then the portion not covered by the photoresist layer is etched by ICP etching. Thereby, a pattern of the desired current blocking layer 125 is formed on the surface of the p-type GaN layer 121. A cerium oxide insulating material is deposited on the recessed holes to form a current blocking layer 125 as shown in FIG. 3D. The current blocking layer 125 has a depth of about 1/3 to 2/3 of the thickness of the p-type GaN layer 121.

At this time, a positioning hole may be formed at any position of the semiconductor layer by an ICP etching method, and the positioning hole extends from the p-type GaN layer 121 to the n-type GaN layer 123 for use in the subsequent current blocking layer 125 and the n-type GaN layer 123. The precise positioning of the etched pattern 125 is used.

A reflective layer 15 having a high reflectance may be deposited on the p-type GaN layer 121 as needed, as shown in FIG. 3E. The reflective layer 15 may be a Bragg reflection layer or a metal specular reflection layer made of a metal such as silver, nickel, aluminum, copper or gold. The purpose of the reflective layer 15 is to reflect the light emitted from the active layer 122 toward the p-type GaN layer 121 and emit it from the surface of the n-type GaN layer 123, thereby improving the light-emitting efficiency of the entire light-emitting diode. In the present embodiment, the reflective layer 15 is a silver layer. The method of depositing the metal layer can be achieved by electron beam, sputtering, vacuum evaporation or electroplating.

Referring to FIG. 3F, the p-type GaN layer 121 is bonded to the thermally conductive substrate 11 by the reflective layer 15. The bonding method can be combined with a Si substrate or a metal substrate by a high temperature and high pressure method, or a thermally conductive substrate 11 can be formed by electroplating. In the present embodiment, a layer of metallic nickel is electroplated on the reflective layer 15 by electroplating. This layer of metallic nickel is used as the thermally conductive substrate 11.

Referring to Fig. 3G, the sapphire substrate 16 is peeled off from the above structure. The stripping method may be a method of mechanically cutting or using electromagnetic radiation to decompose the semiconductor layer or laser cutting. In the present embodiment, the sapphire substrate 16 is peeled off by excimer laser cutting. The n-type GaN layer 123 is exposed.

Referring to FIG. 3H, an etched hole 124 having a graded distribution density and size is etched on the surface of the n-type GaN layer 123 by an ICP etching method, and the pattern of the etched holes 124 is complementary to the pattern of the current blocking layer 125. That is, where the etching hole 124 is provided on the surface of the n-type semiconductor layer 123, the current blocking layer 125 is not provided at the corresponding position of the p-type semiconductor layer 121; and where the etching hole 124 is not provided, the p-type semiconductor layer 121 is provided. A current blocking layer 125 is disposed at a corresponding location. The pattern layer 125 is etched to a depth of about 1/3 to 2/3 of the thickness of the n-type GaN layer 123.

Referring to FIG. 3I, a transparent electrode layer 13 is deposited on the surface of the n-type GaN layer 123, the surface of the transparent electrode layer 13 completely covering the surface of the n-type GaN layer 123, the pattern shape of the transparent electrode layer 13 and the surface shape of the n-type GaN layer 123. Consistent, it also coincides with the pattern of the current blocking layer 125. That is, where the pattern of the transparent electrode layer 13 is provided, the current blocking layer 125 is provided at a corresponding position of the p-type semiconductor layer 121.

In fact, the transparent electrode layer 13 may be deposited on the surface of the n-type GaN layer 123, and then an etched pattern 125 of a graded density and size is etched on the surface of the n-type GaN layer 123 by an ICP etching method.

If necessary, an n-type contact pad 14 may be formed on the surface of the transparent electrode layer 13, as shown in FIG. 3J, as a connection region between the light-emitting diode and the external power source. The n-type contact pad 14 is made of a metal such as silver, gold, copper, aluminum, or nickel or an alloy of any two of the above. In the present embodiment, the n-type contact pad 14 is a silver layer contact pad.

In the fabrication process described above, the etched holes 124 have the highest density of distribution closest to the electrode contact pads 14. In a direction away from the electrode contact pads 14, the distribution density and size of the etched holes 124 gradually become smaller, forming a pattern having a gradual distribution density and size. In the present embodiment, the etch holes 124 are distributed around the electrode contact pads 14, and the etch holes 124 enclose a plurality of annular patterns of different radii. Each annular pattern consists of etched holes 124 of the same size and shape. The etched holes 124 of this embodiment are circular in shape, and the circular etched holes 124 have the largest diameter near the electrode contact pads 14. In the direction away from the electrode contact pad 14, the diameter of the etched hole 124 gradually becomes smaller. Moreover, in the direction away from the electrode contact pad 14, the distance between the annular patterns is also larger, and the distance between the etching holes 124 constituting the same annular pattern is also larger.

The pattern of the etched holes 124 constituting the annular pattern may also be an equilateral triangle, a square, a regular hexagon, a regular polygon, or other regular or irregular shape, as needed. The size of the etched holes 124 gradually decreases in a direction away from the electrode contact pads 14.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

11‧‧‧thermal substrate

121‧‧‧p-type semiconductor layer

122‧‧‧Active layer

123‧‧‧n type semiconductor layer

13‧‧‧Transparent electrode layer

14‧‧‧Electrode contact pads

124‧‧‧ etching holes

125‧‧‧current barrier

15‧‧‧reflective layer

16‧‧‧Sapphire substrate

1 is a schematic structural view of a light emitting diode according to an embodiment of the present invention.

Fig. 2 is a view showing the pattern shape of an etched hole in the embodiment of the present invention.

3A-3J are schematic cross-sectional views showing a process of fabricating a light-emitting diode according to an embodiment of the present invention.

11‧‧‧thermal substrate

121‧‧‧p-type semiconductor layer

122‧‧‧Active layer

123‧‧‧n type semiconductor layer

13‧‧‧Transparent electrode layer

14‧‧‧Electrode contact pads

124‧‧‧ etching holes

125‧‧‧current barrier

15‧‧‧reflective layer

Claims (10)

A light-emitting diode comprising: a heat-conducting substrate; and a semiconductor layer, a transparent electrode layer and an electrode contact pad formed on the surface of the heat-conducting substrate, wherein the semiconductor layer comprises a p-type semiconductor layer and an active layer which are sequentially stacked on the heat-conductive substrate And an n-type semiconductor layer, the transparent electrode layer and the electrode contact pad are disposed on the surface of the n-type semiconductor layer, and a plurality of etching holes are disposed on a surface of the n-type semiconductor layer opposite to the active layer, and the hole is etched at a place closest to the electrode contact pad The distribution density is the highest, the distribution density of the etched holes gradually decreases along the direction away from the electrode contact pads, and the size of the etched holes is gradually reduced, and a current blocking layer is disposed on the surface of the p-type semiconductor layer opposite to the active layer. The pattern of the current blocking layer is complementary to the pattern of etched holes. The light-emitting diode according to claim 1, wherein the electrode contact pad is disposed at a center of the light-emitting diode, and a plurality of circles surrounded by the etched holes are distributed around the electrode contact pads. The annular pattern has a greater distance between adjacent annular patterns in a direction away from the electrode contact pads. The light-emitting diode according to claim 1, wherein the semiconductor layer is made of gallium nitride, aluminum gallium nitride or indium gallium nitride. The light-emitting diode according to claim 1, wherein the light-emitting diode further comprises a positioning hole extending from the p-type semiconductor layer to the n-type semiconductor layer, the positioning hole is for current The pattern of the barrier layer and the etched holes is exactly aligned. The light-emitting diode according to claim 1, wherein the light-emitting diode further comprises a reflective layer having a high reflectivity, the reflective layer being disposed between the thermally conductive substrate and the p-type semiconductor layer. The light-emitting diode according to claim 1, wherein the current blocking layer is made of a ceria material. The light-emitting diode according to claim 1, wherein the thickness of the current blocking layer is 1/3 to 2/3 of the thickness of the p-type semiconductor layer, and the depth of the etching hole is 1/ of the thickness of the n-type semiconductor layer. 3~2/3. A method for manufacturing a light-emitting diode, the steps of which are:
Providing a sapphire substrate;
Forming an n-type semiconductor layer, an active layer, and a p-type semiconductor layer sequentially on the sapphire substrate;
Etching a pattern required for the current blocking layer on the surface of the p-type semiconductor layer, and then filling the pattern with an electrically insulating medium to form a current blocking layer;
Depositing a reflective layer on the surface of the p-type semiconductor layer;
Bonding the p-type semiconductor layer to the thermally conductive substrate and removing the sapphire substrate;
Etching the surface of the n-type semiconductor layer opposite to the active layer to form a desired etch hole, and the pattern formed by etching the hole is complementary to the pattern of the current blocking layer;
Forming a transparent electrode layer on the surface of the n-type semiconductor layer;
An electrode contact pad is formed on the surface of the transparent electrode layer. The method for fabricating a light-emitting diode according to claim 8, wherein a metal nickel layer is formed as a heat conductive substrate on the p-type semiconductor layer by electroplating. The method for fabricating a light-emitting diode according to claim 8, wherein the manufacturing method comprises forming a positioning hole extending from the p-type semiconductor layer to the n-type semiconductor layer.