JP2006019459A - Epitaxial wafer for light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer for a light-emitting diode having an irregularly roughened outermost surface at the stage of a wafer previously without a positive roughening treatment after a growth. <P>SOLUTION: The epitaxial wafer for the light-emitting diode having a double hetero structure laminates an n-type clad layer 2 composed of AlGaInP, an active layer 3, a p-type clad layer 4, and a current dispersion layer 5 composed of AlGaAs or AlGaInP on a conductive substrate 1. In such an epitaxial wafer for the light-emitting diode, a group V gas is supplied or is not supplied at a constant interval during the growth of the current dispersion layer 5 on the outermost surface, thus intentionally forming irregularities 5a to the current dispersion layer 5 as the outermost surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventional epitaxial wafers for high-brightness LEDs are often produced using vapor phase growth methods such as metal organic chemical vapor deposition (MOVPE) and hydride VPE methods. The MOVPE method will be described as an example.

In the growth, a crystal substrate is heated with a heater, and hydrogen or nitrogen is used as a carrier gas, and trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), or trimethylindium (TMI) as a group III material, or arsine as a group V material. (AsH ₃ ) and phosphine (PH ₃ ) are supplied, and crystals are grown by a thermal decomposition reaction.

FIG. 3 shows a cross-sectional structure of an epitaxial wafer for LEDs having a double heterostructure of (Al _x Ga _{1 -x} ) _y In _{1 -y} P (0 ≦ x ≦ 1, 0 <y ≦ 1).

When manufacturing this LED epitaxial wafer, an n-type cladding layer 2 made of n-type AlGaInP, an active layer 3 and a p-type cladding layer 4 made of p-type AlGaInP on a substrate 1 made of n-type GaAs heated to 650 ° C. Are sequentially stacked 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) The current spreading layer 6 made of <1) is grown by lamination. At the same time as the growth of the current spreading layer 6, the heater is turned off and the temperature is lowered to complete the growth.

  The surface of the epitaxial wafer for LED thus grown is conventionally a mirror surface, and the surface flatness is very good.

  A chip manufacturing process is performed on the epitaxial wafer for LED, an n-type electrode and a p-type electrode are formed, and dicing into a chip of a predetermined size completes the LED chip. The active layer emits light by passing a current between the electrodes of the completed LED chip. The emitted light spreads in various directions and is extracted outside as light.

  It is difficult to extract all the light emitted from the active layer to the outside. This is because some of the emitted light is absorbed when propagating through the crystal, or is totally reflected at the interface between the outermost surface of the wafer and air and is not emitted to the outside. In particular, a wafer surface produced by a vapor phase growth method such as the MOVPE method has good flatness, so that total reflection of light easily occurs and the light extraction efficiency is lowered. For this reason, the emission intensity of the LED is reduced.

  The luminous efficiency of the LED is proportional to the product of the internal quantum efficiency and the light extraction (external quantum efficiency). The internal quantum efficiency has reached 70% due to the improvement of the LED structure and crystallinity, and already has a saturation tendency. On the other hand, the extraction efficiency usually remains below 20%. That is, the low light emission efficiency is mainly due to the low extraction efficiency.

In a GaAs-based LED, it has been proposed that the entire surface of the chip is roughened by wet etching (see, for example, Patent Document 1). According to this proposal, by providing irregularities on the chip surface, irregularities with various angles are formed on the light extraction surface when viewed microscopically, thereby increasing the effective solid angle and improving the light extraction efficiency. To do. For this surface unevenness, a nitric acid-based etchant, hydrofluoric acid, or an ammonia-hydrogen peroxide-based etchant is used.
Japanese Unexamined Patent Publication No. 2000-196141 (FIG. 1)

  As described above, in the LED, it is effective to form fine irregularities on the element surface in order to improve the light extraction efficiency of the light emitting element by increasing the light extraction efficiency.

  However, roughening the entire surface of each LED chip after cutting it out from the LED epitaxial wafer as in Patent Document 1 causes an increase in the number of steps and increases the cost. Therefore, without roughening after the growth of the epitaxial wafer, fine irregularities are already formed on the surface of the LED at the wafer stage, thereby improving the light extraction efficiency and improving the LED light emission efficiency. It is desirable to provide a simple means for improvement.

  Accordingly, an object of the present invention is to solve the above-mentioned problems, and has an outermost surface roughened by unevenness at the stage of a wafer, and therefore there is no need to dare to roughen the LED chip after the growth of the epitaxial wafer. An epitaxial wafer is provided.

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

Light emitting diode (LED) epitaxial wafer according to a first aspect of the invention, on a substrate, made of _{(Al x Ga 1-x)} y In 1-y P (0 ≦ x ≦ 1,0 <y ≦ 1) n-type cladding layer, active layer, p-type cladding layer and Al _x Ga _1-x As (0 ≦ x <1) or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 In an epitaxial wafer for a light emitting diode (LED) having a double hetero structure in which current dispersion layers made of <y ≦ 1) are laminated, supply of a group V gas is inserted at regular intervals during the growth of the outermost current dispersion layer. Or having a structure in which unevenness is intentionally provided in the outermost current spreading layer by cutting or cutting.

  According to a second aspect of the present invention, in the epitaxial wafer for a light emitting diode (LED) according to the first aspect, the unevenness intentionally provided in the outermost current spreading layer is a group V gas supply during the growth of the current spreading layer. It is formed by setting the on / off interval to 5 seconds or more and 20 seconds or less.

<Key points of the invention>
The LED epitaxial wafer of the present invention is a surface layer (Al _x Ga _1-x) in order to reduce the probability that light emitted from the active layer is totally reflected on the surface when emitted from the surface of the LED into the air. ) The surface of the current spreading layer made of As (0 ≦ x <1) or (Al _x Ga _1−x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) is intentionally roughened. ing. As a means for roughening unevenness, wet etching performed after forming a chip is known (see, for example, Patent Document 1), but in the present invention, AsH that becomes a group V source gas during the growth of a current dispersion layer is known. _By turning on and off the supply of ₃ and PH ₃ at regular intervals, the growth surface is intentionally roughened.

  If the supply of the group V gas is cut off during the growth, the group V partial pressure in the growth atmosphere is lowered, so that the group V is detached from the grown crystal, and the growth surface becomes rough. However, if the supply is cut off for a long time, Group III droplets are generated on the grown surface, and the quality of the crystal is significantly deteriorated. If the quality of the crystal is deteriorated, the device characteristics such as the decrease in luminance and the lifespan of the device are deteriorated.

  When the time to cut the supply and the degree of surface roughness were examined, the crystal surface was mirror-like when it was shorter than 5 seconds. When the time exceeded 5 seconds, the surface became rough, and when the time exceeded 20 seconds, Ga droplets were generated. From this, the time to cut off the supply is between 5 seconds and 20 seconds.

  According to the present invention, the following excellent effects can be obtained.

  The epitaxial wafer for LED of the present invention is grown at the wafer stage, that is, while the supply of the group V gas is turned on and off at regular intervals during the growth of the current distribution layer on the outermost surface. An irregularity is intentionally formed in the current spreading layer. Therefore, according to the present invention, the surface of the wafer is roughened by a simple method of turning on and off the supply of the group V gas without performing a roughening process after the growth, thereby improving the light extraction efficiency. Thus, the emission intensity when the LED is used can be increased.

Moreover, since the epitaxial wafer for LED of this invention has the uneven surface, the contact area at the time of electrode formation increases, and contact resistance reduces. Thereby, the forward voltage (V _f ) which is one of the LED characteristics can be reduced.

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

  FIG. 1 shows a cross-sectional structure of an LED epitaxial wafer according to this embodiment.

This epitaxial wafer for LED uses the MOVPE method and has conductivity (Al _x Ga _{1 -x} ) _y In _{1 -y} P (0 ≦ x ≦ 1, 0 <) on a substrate 1 made of GaAs. n-type cladding layer 2 made of y ≦ 1), active layer 3, p-type cladding layer 4 made of (Al _x Ga _1−x ) _y In _1−y P (0 ≦ x ≦ 1, 0 <y ≦ 1) Further, Al _x Ga _1-x As (0 ≦ x <1) or (Al _x Ga _1-x ) _y In _1-y P is formed on the p-type cladding layer 4. It has a structure in which a current dispersion layer 5 made of (0 ≦ x ≦ 1, 0 <y ≦ 1) is laminated.

  When this epitaxial wafer for LED is manufactured, an n-type cladding layer 2 made of AlGaInP, an active layer 3 and an AlGaInP are formed on a substrate 1 made of n-type GaAs heated to 650 ° C. by a vapor phase growth method such as MOVPE. The resulting p-type cladding layer 4 is sequentially stacked and grown. Further, a current spreading layer 5 made of AlGaInP or AlGaAs is laminated and grown on the outermost surface. While the current spreading layer 5 on the outermost surface is grown, the supply of the group V gas is turned on and off at regular intervals. By growing, the unevenness 5a is intentionally formed in the current distribution layer 5 on the outermost surface. That is, the top surface of the wafer is roughened.

  In this way, according to the epitaxial wafer for LEDs in which fine irregularities are formed on the element surface at the wafer stage, it is easier to form irregularities on the element surface than in the case of roughening after forming a chip. It is possible to solve the problem of reduction in light extraction efficiency due to total reflection on the outermost surface of the element, increase the light extraction efficiency, and improve the light emission efficiency of the light emitting element.

  Next, the embodiment will be described more specifically in comparison with the conventional example.

[Conventional example]
The epitaxial wafer for LED was grown by the method of the prior art using the MOVPE method. An example of growth is shown.

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 as} Group V materials, and hydrogen selenide as H ₃ dopant (H ₂ Se) and diethyl zinc (DEZ) were supplied as needed for growth.

  FIG. 4 is a schematic cross-sectional view of the grown epitaxial wafer for LED. On a Si-doped GaAs substrate 7, 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 formed. Then, the Zn-doped AlGaAs current dispersion layer 12 was grown in order, and the heater was turned off and cooled simultaneously with the completion of the growth. The grown wafer surface was mirror-like and had good flatness.

〔Example〕
Next, an example of growing an epitaxial wafer for LED according to an embodiment of the present invention by the MOVPE method will be described. A cross section of the epitaxial wafer produced in this example is schematically shown in FIG. 4 differs from the conventional example of FIG. 4 in that a Zn-doped AlGaAs current spreading layer 13 having irregularities 13a is provided on the Zn-doped AlGaInP cladding layer 11 instead of the Zn-doped AlGaAs current spreading layer 12.

As the growth method, the layers up to the Zn-doped AlGaInP cladding layer 11 which is a p-type cladding layer were grown in the same manner as the conventional growth method (FIG. 4). The Zn-doped AlGaAs current distribution layer 13 formed on the Zn-doped AlGaInP cladding layer 11 is supplied with AsH ₃ as a group V material for 10 seconds during its growth, and then turns off the supply for 10 seconds. It grew by repeatedly turning on and off the group gas supply.

  When the surface of the taken-out epitaxial wafer was observed with an electron microscope, the surface was fine and rough.

  The LED epitaxial wafer prepared by the growth method of the above-described conventional example and this example is subjected to a chip manufacturing process, an n-type electrode and a p-type electrode are formed, an LED chip is formed, and a current of 20 mA is applied to emit light. The emission intensity was compared.

  In the case of the LED of the wafer (FIG. 4) produced by the conventional growth method, the emission intensity was 100 mcd, whereas in the case of the LED of the wafer (FIG. 2) produced by the production method of this example, the emission intensity was The brightness was improved by 20% in the LED epitaxial wafer of this example.

[Other Examples]
In the above example, growth was performed when the supply of AsH ₃ was turned off and on for 4 seconds, 5 seconds, 20 seconds, and 21 seconds, the surface state was confirmed, and then the wafer was obtained through a chip manufacturing process. The emission intensity of the obtained chips was compared.

  As for the surface state, the surface of the wafer with the growth material supply on / off interval of 4 seconds (Comparative Example 1) was a mirror surface, but the growth material supply on / off interval of 5 seconds and 20 seconds with the epitaxial wafer (other examples) ), The desired irregularities were observed on the surface. Metal particle droplets were generated on the surface of the 21-second wafer (Comparative Example 2).

  In the measurement of the emission intensity, the growth material supply with the on / off interval of 4 seconds was 102 mcd, which was not changed as compared with the growth method of the prior art. On the other hand, when the growth material supply interval was 5 seconds and 20 seconds, the luminance was 115 mcd and 122 mcd, respectively. The remaining 21 seconds had 50 mcd and the brightness was greatly reduced.

  According to the present embodiment, the wafer outermost surface can be easily roughened without being dared to perform a process after growth, so that the light extraction efficiency is improved and the light emission intensity is increased when an LED is formed. .

In addition, since the epitaxial wafer using this embodiment has an uneven surface, the contact area during electrode formation increases and the contact resistance decreases. Thereby, the forward voltage (V _f ) which is one of the LED characteristics can be reduced.

[Modification]
In the above embodiment, as a means for roughening the surface of the current spreading layer, only the supply of the group V is cut off. However, the crystal surface grown by cutting off the supply of both the group III and group V and reducing the group V partial pressure is used. You may grow up while ruining.

It is the schematic diagram which showed the cross-section of the epitaxial wafer for light emitting diodes (LED) concerning embodiment of this invention. It is the schematic diagram which showed the cross-section of the epitaxial wafer for light emitting diodes (LED) concerning the Example of this invention. It is the schematic diagram which showed the cross-section of the conventional epitaxial wafer for light emitting diodes (LED). It is the schematic diagram which showed the cross-section of the other conventional epitaxial wafer for light emitting diodes (LED).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 N-type cladding layer 3 Active layer 4 P-type cladding layer 5 Current dispersion layer 5a Unevenness 6 Current dispersion layer 7 Si-doped GaAs substrate 8 Se-doped GaAs buffer layer 9 Se-doped AlGaInP cladding layer 10 Undoped AlGaInP active layer 11 Zn-doped AlGaInP cladding layer 12 Zn-doped AlGaAs current spreading layer 13 Zn-doped AlGaAs current spreading layer 13 a Uneven

Claims (2)

An n-type cladding layer, an active layer, a p-type cladding layer, and an Al _x Ga ₁ layer made of (Al _x Ga _{1 -x} ) _y In _{1 -y} P (0 ≦ x ≦ 1, 0 <y ≦ 1) are formed on a substrate. _-x As (0 ≦ x <1) or (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 <y ≦ 1) laminated double hetero structure In an epitaxial wafer for light emitting diodes having
For light-emitting diodes, wherein the outermost current spreading layer is intentionally provided with irregularities by turning on or off the supply of group V gas at regular intervals during the growth of the outermost current spreading layer Epitaxial wafer. In the epitaxial wafer for light emitting diodes of Claim 1,
The unevenness provided intentionally in the current distribution layer on the outermost surface is formed by setting the on / off interval of the V group gas supply during the growth of the current distribution layer to be 5 seconds or more and 20 seconds or less. Epitaxial wafer for light emitting diode.

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