JP2005079266A - Light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting diode having solved a problem that light extracting efficiency is lowered due to total reflection at the outermost front surface of a wafer by providing an uneven surface attained by a method suitable for a growth process. <P>SOLUTION: In a light emitting diode of double-hetero structure, an n-type clad layer formed of (Al<SB>x</SB>Ga<SB>1-x</SB>)<SB>y</SB>In<SB>1-y</SB>P (0≤x≤1, 0<y≤1), a light emitting layer, a p-type clad layer, and a current dispersing layer formed of Al<SB>x</SB>G<SB>1-x</SB>As (0≤x<1) or (Al<SB>x</SB>Ga<SB>1-x</SB>)<SB>y</SB>In<SB>1-y</SB>P (0≤x≤1, 0<y≤1) are sequentially formed on a conductive substrate using a chemical vapor deposition method. Projected and recessed portions 5a, 13a are formed on the surface of the current dispersing layer 5 or 13 being the outermost surface by conducting heat treatment after the growth of a film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting diode (LED) in which an outermost surface layer is intentionally roughened to improve light extraction efficiency.

  Conventional epitaxial wafers for high-intensity light-emitting diodes are often produced using vapor phase growth methods such as MOVPE and hydride VPE.

A MOVPE (Metal Organic Vapor Phase Epitaxy) method will be described as an example. In the growth, the crystal substrate is heated with a heater, and hydrogen or nitrogen is used as a carrier gas therefor, TMG (trimethylgallium), TMA (trimethylaluminum), TMI (trimethylindium), or AsH as a V group material. ₃ (arsine) and PH ₃ (phosphine) are supplied and crystals are grown by thermal decomposition reaction.

FIG. 2 is a schematic cross-sectional view of a light emitting diode having a double hetero structure of (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1). An n-type AlGaInP clad layer 2, an active layer 3, a p-type AlGaInP clad layer 4 on an n-type GaAs substrate 1 heated to 650 ° C., and (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) or Al _x Ga _1-x As (0 ≦ x <1) current spreading layer 6 is laminated and grown. At the same time as the growth of the current spreading layer 6 is completed, the heater is turned off and the temperature is lowered to complete the growth.

  The wafer thus grown is conventionally a mirror surface, and the surface flatness is very good. When a chip manufacturing process is performed on this wafer to form an n-type electrode and a p-type electrode, an LED chip is completed. The active layer 3 emits light by passing a current between the electrodes of the completed chip. The emitted light spreads in various directions and is extracted outside as light.

  However, it is difficult to extract all the light emitted from the active layer to the outside. This is because some are absorbed when propagating through the crystal, or are totally reflected at the interface between the wafer outermost surface and air and are not released to the outside.

  In order to increase the light extraction efficiency, a processing method for roughening the surface of pellets obtained by cutting semiconductor wafers having pn junctions one by one into chips is already known. When the surface of the pellet is roughened, the probability that the light is totally reflected at the interface between the light emitting surface and the air is lowered, so that it is considered that the extraction efficiency can be increased.

For GaAsP mixed crystals, a light-emitting diode is known in which fine pellets are formed on the main surface by treating the pellet with an etching solution containing Br ₂ or I ₂ in an aqueous solution (for example, Patent Documents). 1).
JP 2000-196141 A

  As described above, it is difficult to extract all the light emitted from the active layer to the outside. This is because some are absorbed when propagating through the crystal, or are totally reflected at the interface between the wafer outermost surface and air and are not released to the outside. In particular, since the wafer surface manufactured by the vapor phase growth method has good flatness, total reflection of light easily occurs, and the light extraction efficiency is lowered. For this reason, the light emission intensity of the light emitting diode is reduced.

  However, Patent Document 1 is a technique for roughening the surface by wet etching, and is poorly adaptable as a technique for roughening the surface of a wafer produced by vapor phase growth.

  Therefore, the object of the present invention is to solve the above-mentioned problems and to have a rough surface roughened by a method compatible with the growth process, thereby solving the problem of reduction in light extraction efficiency due to total reflection on the outermost surface of the wafer. It is to provide a light emitting diode having a large size.

  In order to achieve the above object, the present invention is configured as follows.

The light-emitting diode according to the first aspect of the present invention is obtained by forming (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) on a conductive substrate using a vapor phase growth method. N-type cladding layer, light-emitting layer, p-type cladding layer and Al _x G _1-x As (0 ≦ x <1) or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦) A light-emitting diode having a dove heterostructure in which current distribution layers of 1 and 0 <y ≦ 1) are sequentially stacked are characterized in that unevenness is formed on the surface of the current distribution layer, which is the outermost surface layer, by performing heat treatment after growth. To do.

  According to a second aspect of the present invention, in the light-emitting diode according to the first aspect, the method for forming irregularities on the surface of the current dispersion layer is a heat treatment in a gas atmosphere or in a vacuum.

  According to a third aspect of the present invention, in the light-emitting diode according to the second aspect, the gas atmosphere is hydrogen, nitrogen, or an inert gas.

  Argon is preferably used as the inert gas.

  According to a fourth aspect of the present invention, in the light emitting diode according to any one of the first to third aspects, the temperature of the heat treatment is a growth temperature of the current spreading layer.

  According to a fifth aspect of the present invention, in the light-emitting diode according to the fourth aspect, after the growth of the current dispersion layer is completed, heat treatment is performed at a growth temperature for a predetermined time in a state where only hydrogen as a carrier gas is supplied. An uneven surface is formed on the surface of the dispersion layer.

<Key points of the invention>
In the present invention, in order to reduce the probability that the light emitted from the active layer is totally reflected on the surface when emitted from the wafer surface into the air, the surface layer is Al _x Ga _1-x As (0 ≦ x <1). ) Or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) The surface of the current dispersion layer is intentionally roughened. Wet etching is known as a means for roughening the unevenness (Patent Document 1: Japanese Patent Laid-Open No. 2000-196141), but in the present invention, heat treatment is performed during the wafer growth process to slightly heat the crystal surface. It can be disassembled and roughened. As an atmosphere for the heat treatment, argon or the like, which is an inert gas, is used in addition to nitrogen and hydrogen used in the growth process. Moreover, you may carry out in a vacuum.

  The reason why nitrogen or hydrogen is used in the heat treatment atmosphere in the present invention is that hydrogen or nitrogen is generally used as a carrier gas for the raw material in the MOVPE method. Since hydrogen and nitrogen are inert to the grown crystal and are used during the growth process by the MOVPE method, a new heat treatment process is not required if heat treatment is performed consistently after the growth is completed. This is because heat treatment can be performed easily and in a short time. It is more suitable for being inert to the grown crystal even in a vacuum and being easily performed during the growth process by the MOVPE method.

  As described above, according to the present invention, unevenness is formed on the surface of the current spreading layer, which is the outermost surface layer, by performing a heat treatment after growth. Very good compatibility with vapor phase growth.

  Therefore, if the present invention is used, the outermost surface of the wafer can be easily roughened, so that the light extraction efficiency is improved and the light emission intensity is increased when a light emitting diode is formed.

  Moreover, since the surface of the epitaxial wafer using the present invention is uneven, the contact area during electrode formation increases and the contact resistance decreases. Thereby, the forward voltage (Vf) which is one of the LED characteristics can be reduced.

  Hereinafter, embodiments of the present invention will be described based on the illustrated examples.

<Example 1>
First, as a conventional example, an epitaxial wafer for LED (FIG. 2) was grown by a conventional method using metal organic vapor phase epitaxy. An example of the growth of this conventional example is shown below.

In FIG. 2, an n-type AlGaInP cladding layer 2, an undoped AlGaInP active layer 3, a p-type AlGaInP cladding layer 4 on an n-type GaAs substrate 1 heated to 650 ° C., and (Al _x Ga _1-x ) _y In on the outermost surface. A current spreading layer 6 of _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) or Al _x Ga _1-x As (0 ≦ x <1) is stacked and grown. At the same time as the growth of the current spreading layer 6, the heater was turned off and cooled. The grown wafer surface was mirror-like and had good flatness.

  Next, the growth of the epitaxial wafer for LEDs (FIG. 1) produced by the growth method according to this example will be described.

  Up to the AlGaInP or AlGaAs current spreading layer 6 which is the outermost surface layer was grown in the same manner as the conventional growth of FIG. After the growth of the current dispersion layer 6 was completed, the supply of the raw material was cut off, and heat treatment was performed at the growth temperature for 15 minutes using only hydrogen as a carrier gas, and then cooled and taken out.

  When the surface of the taken-out wafer was observed with an electron microscope, the surface of the current dispersion layer 6 was finely roughened. A schematic cross-sectional view of the produced epitaxial wafer is shown in FIG. In FIG. 1, an AlGaInP or AlGaAs current distribution layer having irregularities 5 a is indicated by reference numeral 5.

  The wafers produced by the growth methods of the conventional example (FIG. 2) and the present example (FIG. 1) were each subjected to a chip production process to form an n-type electrode and a p-type electrode, thereby producing a light-emitting diode chip. These light emitting diode chips were caused to emit light by flowing a current of 20 mA, and the light emission intensities were compared. The wafer light emitting diode chip (FIG. 2) produced by the conventional growth method had a light emission intensity of 100 mcd, whereas the wafer light emitting diode chip (FIG. 1) of the manufacturing method of this embodiment had a brightness of 120 mcd and 20%. Had improved.

<Example 2>
First, as a conventional example, an epitaxial wafer for LED (FIG. 3) was grown by a conventional method using metal organic vapor phase epitaxy. An example of growth is shown below.

The substrate is heated to 650 ° C. with a heater, and hydrogen is used as a carrier gas therefor, TMG, TMA, TMI as group III materials, AsH ₃ and PH _{3 as} group V materials, and H ₂ Se (selenium as a dopant). Hydrogen chloride) and DEZ (diethylzinc) were supplied as needed for growth.

  FIG. 3 is a schematic cross-sectional view of a grown epitaxial wafer for LED (conventional example). A Se-doped GaAs buffer layer 8, a Se-doped AlGaInP cladding layer 9, an undoped AlGaInP active layer 10, and a Zn-doped AlGaInP cladding layer 11 are sequentially stacked on the Si-doped GaAs substrate 7, and finally a Zn-doped AlGaAs current distribution layer 12 is grown. When the growth was completed, the heater was turned off and cooled. The grown wafer surface was mirror-like and had good flatness.

  Next, the growth of the epitaxial wafer for LEDs (FIG. 4) produced by the growth method according to the present invention will be described.

The growth up to the Zn-doped AlGaAs current spreading layer 12 which is the outermost surface layer is the same as the conventional growth of FIG. After the growth of the current spreading layer 12, the supply of the raw materials TMG, TMA, DEZ and AsH ₃ was cut off, and the heat treatment was carried out at the growth temperature for 15 minutes as it was using only the carrier gas, and then cooled and taken out.

  When the surface of the taken-out wafer was observed with an electron microscope, the surface of the current dispersion layer 12 was finely roughened. A schematic cross-sectional view of the produced epitaxial wafer is shown in FIG. In FIG. 4, a Zn-doped AlGaAs current distribution layer having unevenness 13 a is indicated by reference numeral 13.

  The wafers produced by the growth methods of the conventional example (FIG. 3) and the present example (FIG. 4) were each subjected to a chip production process to form an n-type electrode and a p-type electrode, thereby producing a light-emitting diode chip. These light emitting diode chips were caused to emit light by passing a current of 20 mA, and the light emission intensity was compared. The light emitting diode chip (FIG. 3) of the wafer produced by the conventional growth method had an emission intensity of 100 mcd, whereas the wafer light emitting diode chip (FIG. 4) of the manufacturing method of this example was 120 mcd, which is 20%. The brightness was improved.

<Other embodiments and modifications>
In the above embodiment, the heat treatment for forming the unevenness is performed consistently after the growth is completed, but it is also conceivable to take it out of the MOVPE apparatus and perform the heat treatment in another heat treatment furnace to roughen the surface.

In the above embodiment, the atmosphere during the heat treatment was hydrogen, or a mixed gas by mixing AsH ₃ in a trace amount. Furthermore, a mixed gas atmosphere of hydrogen, nitrogen, and argon may be used.

It is a chip | tip cross-section schematic diagram of the epitaxial wafer for light emitting diodes concerning the Example of this invention. It is a cross-sectional schematic diagram of the epitaxial wafer for light emitting diodes of a prior art. It is a cross-sectional schematic diagram of the epitaxial wafer for light emitting diodes of a prior art. It is a chip | tip cross-section schematic diagram of the epitaxial wafer for light emitting diodes concerning the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Cladding layer 3 Active layer 4 Cladding layer 5 and 6 Current distribution layer 5a Concavity and convexity 7 Substrate 8 Buffer layer 9 Cladding layer 10 Active layer 11 Cladding layer 12 and 13 Current dispersion layer 13a Concavity and convexity

Claims (5)

An n-type cladding layer made of (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) is formed on a conductive substrate using a vapor phase growth method, A current comprising a p-type cladding layer and Al _x G _1-x As (0 ≦ x <1) or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) In a light-emitting diode having a dove heterostructure in which dispersion layers are sequentially stacked,
A light emitting diode characterized by forming irregularities on the surface of a current spreading layer which is the outermost surface layer by performing a heat treatment after growth. The light emitting diode according to claim 1.
The light emitting diode according to claim 1, wherein the method for forming irregularities on the surface of the current spreading layer is a heat treatment in a gas atmosphere or in a vacuum. The light emitting diode according to claim 2.
A light emitting diode, wherein the gas atmosphere is hydrogen, nitrogen, or an inert gas. In the light emitting diode in any one of Claims 1-3,
The light-emitting diode, wherein the temperature of the heat treatment is a growth temperature of the current spreading layer. The light emitting diode according to claim 4.
After completion of the growth of the current spreading layer, light-emitting diodes are characterized in that the surface of the current spreading layer is formed by heat treatment as it is for a predetermined time while flowing only hydrogen as a carrier gas. .

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