JPH11354845A - Gan compound semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin GaN compound semiconductor light emitting element in which optimal emission brightness can be attained depending on the use while reducing power consumption. SOLUTION: An n electrode 5 is formed on one side of a substrate 1 composed of GaN doped with n-type impurities having the other side laminated sequentially with an n-type layer 2 of GaN, an active layer 3 and a p-type layer 4 of GaN. A p electrode 6 is formed on the p-type layer 4 and a trench 7 penetrates the active layer 3 from the surface of the p-type layer 4 into the n-type layer 2 while forming a closed circle in plan view. The part surrounded by the trench 7 provides a mesa 8 and the p electrode 6 is arranged on the surface thereof while conducting therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an LED for emitting blue light, and more particularly to optimizing lattice matching with an n-type layer so as to obtain light emission luminance required for an application with low power. The present invention relates to a GaN-based compound semiconductor light emitting device.

[0002]

2. Description of the Related Art GaN, Ga
A device utilizing a GaN-based compound semiconductor such as AlN, InGaN, and InAlGaN has been conventionally known. In the development process of LED using GaN compound semiconductor,
Various materials have been sought for a substrate for growing a compound semiconductor crystal on its surface, and sapphire is mainly used in many cases.

FIG. 2 shows an example of a conventional GaN-based compound semiconductor light emitting device. FIG. 2A is an external perspective view, and FIG. 2B is a schematic longitudinal sectional view.

In FIG. 1, a substrate 51 using sapphire is shown.
An n-type layer 52 of GaN and a p-type layer 53 of GaN are formed on each other, and a p-side translucent electrode 54 is formed on the surface of the p-type layer 53 in the illustrated example. A p-side electrode pad 53a is provided on the surface of the p-side translucent electrode 54, and an n-side electrode pad 52a is provided on a portion where a part of the p-type layer 53 is etched to expose the n-type layer 52. Has formed. Then, as is well known, the n-type layer 52 and the p-type layer 53
Are formed by epitaxial growth by metalorganic vapor phase epitaxy, and the p-side and n-side electrode pads 53a, 52a are formed by vapor deposition of a metal such as Al or Ti.

[0005] The above is an outline of the structure. Actually, between the substrate 51 and the n-type layer 52, the sapphire and n
In addition to providing a buffer layer for buffering lattice mismatch between the mold layer 52 and the n-type GaN, a p-type clad layer, a p-type contact layer, and the like are formed. Then, the n-type layer 52 and the p-type layer 53
An active layer 55 of, for example, InGaN is formed between these layers, and this active layer 55 becomes a light emitting region.

[0006]

However, since the substrate 51 is made of insulating sapphire, both the n-side and p-side electrode pads 52a and 53a are provided on the main light extraction surface side opposite to the substrate 51. There is a restriction that there is only. Therefore, in the case of an assembly in which the board 51 is mounted on a printed board such as a lead frame of an LED lamp or a display panel, these n-side and p-side electrode pads 52
It is necessary to bond wires to both a and 53a. Therefore, the number of assembly steps is increased, and the wire protrudes greatly above the light emitting element.
There is also a limit in thinning products such as chip LEDs after resin sealing.

The sapphire of the substrate 51 and the n-type layer 52
There is a lattice mismatch and a difference in coefficient of thermal expansion between the n-type GaN and the n-type GaN. A buffer layer is provided to absorb these factors and grow an epitaxial layer having a high crystallinity. However, even if such a buffer layer is provided at present, a high crystallinity epitaxial layer cannot be formed. No growth has been obtained. Therefore, mainly due to the lattice mismatch, the luminance of light emitted by the active layer 55 is affected to some extent.

On the other hand, in a light emitting display device using an LED, it is a major premise that a light emission luminance corresponding to each application can be obtained. However, it is required to reduce power consumption as in a mobile phone, for example. Often. This reduction in power consumption can be dealt with to some extent by reducing the size of the light emitting element and narrowing down the current.

However, even in the light emitting device using the GaN-based compound semiconductor shown in FIG. 2, the substrate 51 is formed into a wafer state, and n-type GaN or p-type GaN is grown thereon, and then dicing is performed by a dicer into chips. Step on. Since this dicing is mechanical using shearing due to the rotation of a diamond blade, there is a lower limit to the size of a chip that can be diced. Also, in the process of mounting the chip on the lead frame after dicing, if the chip is too small, it becomes difficult to handle and the product yield is affected. Therefore, even if an attempt is made to reduce the power consumption by reducing the size of the light emitting element, it is not possible at the present stage to take appropriate measures in terms of manufacturing.

As described above, in the GaN-based compound semiconductor light-emitting device having sapphire as the substrate 51, even if it is desired to optimize a light-emitting display device which is particularly required to be small in size and low in power consumption, the luminous luminance and power consumption cannot be improved. And problems remain to be improved in each aspect of the assembly.

It is an object of the present invention to provide a GaN-based compound semiconductor light-emitting device which consumes a small amount of power, has an appropriate emission luminance according to the intended use, and can be made thin.

[0012]

A GaN-based compound semiconductor light-emitting device according to the present invention comprises a substrate made of GaN doped with an n-type impurity, an n-electrode formed on one surface of the substrate, An n-type GaN layer sequentially stacked on the surface side,
An active layer and a p-type layer of GaN, and a p-electrode formed on the p-type layer, and a depth reaching from the surface of the p-type layer to the inside of the upper end of the n-type layer through the active layer. And a groove that forms a ring having a closed planar shape is provided, a portion surrounded by the groove is used as a mesa, and the p-electrode is conductively arranged on the surface of the mesa.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a method of forming a substrate made of GaN doped with an n-type impurity, an n-electrode formed on one surface of the substrate, and another surface of the substrate in this order. An n-type layer of GaN, an active layer, a p-type layer of GaN, and a p-electrode formed on the p-type layer;
A groove having a depth extending from the surface of the mold layer to the inside of the upper end of the n-type layer through the active layer and forming a closed ring having a closed planar shape is provided, and a portion surrounded by the groove is used as a mesa. In addition, the p-electrode is conductively arranged on the surface of the mesa, and the current density is increased by consolidating the mesa portion occupying a part, not the entire light emitting layer formed in the light emitting element, as a light emitting region, Light emission with high luminance can be obtained even with a small supply current. In addition, since no light is emitted from the active layer outside the groove, light can be emitted only in the main light extraction surface direction of the light emitting element.

According to a second aspect of the present invention, the width of the groove and the width of the ring around the p-electrode are between the size of the planar shape of the p-type layer and the size of the plane area occupied by the p-electrode. 2. The G according to claim 1, wherein the length is changeable.
Since it is an aN-based compound semiconductor light emitting device and the plane area of the mesa can be freely changed, a product having a specification in which only the light emitting area is changed even if the size of the light emitting device is uniform can be obtained.

Hereinafter, specific examples of the embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a GaN-based compound semiconductor light-emitting device according to an embodiment of the present invention. FIG. 1A is a plan view, and FIG. 1B is a longitudinal sectional view.

Referring to FIG. 1, the light emitting device of the present invention includes a substrate 1 using n-type GaN, and forms an GaN n-type layer 2 on the surface of the substrate 1 without interposing a buffer layer or the like. An active layer 3 of InGaN and a p-type layer 4 of GaN are laminated on the surface of an n-type layer 2.

The n-type layer 2, the active layer 3, and the p-type layer 4 are formed by growing crystals by a metal organic chemical vapor deposition method as in the conventional example. And in the course of this vapor phase growth,
Si or Ge is doped as an n-type impurity to make GaN n-type to form an n-type layer 2, and Mg or Zn is doped as a p-type impurity to make GaN p-type to form a p-type layer 4. You. The p-type layer 4 includes a p-type cladding layer and a p-type cladding layer.
It can also be formed separately for the mold contact layer.

The n-type GaN substrate 1 is a conductive material in which GaN crystals are doped with n-type impurities such as Si and Ge.
The lower surface is provided with an n-electrode 5 formed of a thin film of, for example, Al or Ti by an evaporation method. The n-electrode 5 is formed on almost the entire bottom surface of the substrate 1 and, for example, when mounted on a lead frame of an LED lamp, is conductively fixed by a conductive adhesive such as Ag paste.

On the other hand, the p-electrode 6 is formed on the surface of the p-type layer 4 at a portion included in the mesa 8 surrounded by the frame-shaped groove 7. The p-electrode 6 is formed by depositing Al, Ti, or the like into a pad by an evaporation method, and a wire (not shown) using Au or the like for conduction is bonded to the upper surface thereof. That is, the n-electrode 5 is electrically connected to the mounting surface side of the lead frame of the LED lamp, and the p-electrode 6 is electrically connected to the other lead by a wire, so that a current flowing in the forward direction from the p-electrode 6 to the n-electrode 5 is provided. Can be applied.

The groove 7 has a depth penetrating from the surface of the p-type layer 4 to the upper end of the n-type layer 2 through the active layer 3, and the active layer 3 of the mesa 8 surrounded by the groove 7 is outside the groove 7. From the active layer 3. The groove 7 can be formed by dry etching, processing using laser light, dicing with a dicer, or the like.

In the above configuration, when the light emitting element is assembled as an LED lamp or a chip LED, the n-electrode 5 is conductively fixed to the mounting surface of the lead frame or the wiring pattern with a conductive adhesive or the like, and one wire is connected. It only needs to be bonded to the p-electrode 6. For this reason, compared with the conventional assembly in which wires are respectively bonded to the p-side and the n-side using a substrate made of insulating sapphire,
The number of steps can be reduced. Further, since the height including the wires is suppressed, it is possible to reduce the thickness of LED lamps and chip LEDs that are finally resin-sealed and commercialized.

Since the substrate 1 is made of n-type GaN,
N-type GaN without a buffer layer
Can be improved in lattice matching with the n-type layer 2 and the difference in thermal expansion can be suppressed to a negligible level. Therefore, an epitaxial layer of n-type layer 2 having a high degree of crystallinity without interposing a buffer layer is obtained on substrate 1, and the epitaxial layer of active layer 3 formed on n-type layer 2 also has a high degree of crystallinity. It becomes a high layer, and the emission luminance of the active layer 3 can be improved.

Since the p-electrode 6 is located substantially at the center of the mesa 8, the current flowing to the n-electrode 5 is concentrated on the portion included in the mesa 8, and the current flows to the active layer 3 outside the groove 7. Does not generate a passing current. Therefore, there is no light emitting component from the active layer 3 outside the groove 7, and only the surface portion of the mesa 8 becomes a light emitting region. In other words, light emission can be performed with an amount of electricity sufficient to make the area of the narrow mesa 8 having a limited central portion as a light emitting surface with respect to the entire planar shape of the light emitting element, so that power consumption can be reduced. For this reason, the entire light-emitting element does not have to be small so that power consumption can be reduced. In the process of manufacturing the light-emitting element, dicing by a dicer or other handling is not hindered, and the product yield is not affected.

Further, the current flowing from the p electrode 6 to the n electrode 5 has a high current density in the active layer 3 portion.
Is excited, and the light emission luminance can be increased. Therefore, even if only the mesa 8 is a light emitting area and the amount of current is small, light emission of a predetermined luminance can be obtained. For example, power consumption can be suppressed and light emission luminance can be obtained to some extent. It can be optimally used for a type of display device that can be used sufficiently.

[0025]

According to the first aspect of the present invention, since GaN doped with an n-type impurity is used as the substrate, the lattice matching with the n-type GaN layer stacked thereon is high and the difference in thermal expansion is small. Since it can be neglected, the luminance of light emission by the active layer can be improved, and the number of semiconductor thin film laminating steps can be reduced since a buffer layer and the like are not required. Further, the mesa portion occupying a part of the light emitting layer, not the whole, is concentrated as a light emitting region to increase the current density, so that light emission with high luminance can be obtained even with a small supply current, and power consumption can be reduced. In addition, there is no need to reduce the size of the entire light emitting element in order to reduce the power consumption, and an assembly using conventional manufacturing equipment can be used. Furthermore, since there is no light emission from the active layer outside the groove, no light escapes to the side of the light emitting element, and light can be emitted only from the main light extraction surface.

According to the second aspect of the present invention, the area of the mesa can be freely changed, so that a product having a different light emitting area can be obtained.

[Brief description of the drawings]

FIG. 1A is a plan view of a compound semiconductor light emitting device according to an embodiment of the present invention. FIG. 1B is a longitudinal sectional view of FIG.

2A is a schematic perspective view of a conventional compound semiconductor light emitting device, and FIG. 2B is a longitudinal sectional view of FIG.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 n-type layer 3 active layer 4 p-type layer 5 n-electrode 6 p-electrode 7 groove 8 mesa

Claims (2)

[Claims] 1. A substrate made of GaN doped with an n-type impurity, an n-electrode formed on one surface of the substrate, and an n-type layer, an active layer, and a GaN layer sequentially stacked on the other surface of the substrate. A p-type layer of GaN and a p-electrode formed on the p-type layer, having a depth extending from the surface of the p-type layer to the inside of the upper end of the n-type layer through the active layer; A GaN-based compound semiconductor light-emitting device in which a groove that forms a closed ring in a planar shape is provided, a portion surrounded by the groove is used as a mesa, and the p-electrode is conductively arranged on the surface of the mesa. 2. The size of the planar shape of the p-type layer and the p-type layer
2. The GaN-based compound semiconductor light emitting device according to claim 1, wherein a relationship is provided between the plane area occupied by the electrode and the size of the groove and the length of the ring around the p electrode. .