JP2008078493A - EPITAXIAL WAFER FOR AlGaInP-BASED LIGHT EMITTING DIODE AND PRODUCING METHOD THEREOF - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce surface defects of the epitaxial wafer for an AlGaInP-based light emitting diode without deteriorating light emitting diode characteristics. <P>SOLUTION: The producing method of the epitaxial wafer for the AlGaInP-based light emitting diode laminate-forms at least an n-type (Al<SB>x1</SB>Ga<SB>1-x1</SB>)<SB>y1</SB>In<SB>1-y1</SB>P clad layer (3), (Al<SB>x2</SB>Ga<SB>1-x2</SB>)<SB>y2</SB>In<SB>1-y2</SB>P active layer (4), p-type (Al<SB>x3</SB>Ga<SB>1-x3</SB>)<SB>y3</SB>In<SB>1-y3</SB>P clad layer (5) and current diffusion layer (6) composed of GaP on a conductive substrate (1) using a metal organic vapor phase epitaxy. When the current diffusion layer (6) composed of GaP is grown, the current diffusion layer (6) is grown where the growing temperature of a GaP layer (6a) at the primary stage of the growth is higher than that of the p-type (Al<SB>x3</SB>Ga<SB>1-x3</SB>)<SB>y3</SB>In<SB>1-y3</SB>P clad layer (5) and thereafter, the remaining GaP layer (6b) is grown at a low temperature equal to or lower than the growing temperature of the p-type (Al<SB>x3</SB>Ga<SB>1-x3</SB>)<SB>y3</SB>In<SB>1-y3</SB>P clad layer (5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an AlGaInP-based epitaxial wafer for light-emitting diodes using GaP as a current spreading layer and a method for producing the same.

Conventionally, an epitaxial wafer for an AlGaInP-based light emitting diode (LED) is often manufactured using a metal organic vapor phase epitaxy (MOVPE method). In the MOVPE method, a crystal substrate is heated with a heater, and hydrogen or nitrogen is used as a carrier gas, and group III materials such as TMG (trimethylgallium), TMA (trimethylaluminum), TMI (trimethylindium), etc. In this method, AsH ₃ (arsine), PH ₃ (phosphine), or the like, which is a raw material, is supplied, and crystals are grown on the crystal substrate with good alignment by a thermal decomposition reaction.

  In the conventional method of manufacturing an AlGaInP-based double heterostructure light-emitting diode using the MOVPE method, an n-type AlGaInP cladding layer, an undoped AlGaInP active layer serving as a light-emitting portion, and a p-type on an n-type GaAs substrate heated to 650 ° C. An AlGaInP clad layer is grown by lamination, and then the growth temperature is raised to 700 ° C. to grow GaP as a current dispersion layer. The epitaxial wafer thus grown is subjected to a chip formation process. After forming an n-type electrode on the substrate side and a p-type electrode on the current distribution layer, the wafer is cut to produce an LED chip.

As a related technique, in an AlGaInP-based LED element using AlGaInP as a current diffusion layer (current dispersion layer), the AlGaInP current diffusion layer has two layers (or more), and the carrier of the first current diffusion layer close to the active layer The concentration is set to 1 to 3 × 10 ¹⁸ cm ⁻³ , the carrier concentration of the second current diffusion layer far from the active layer is set to 1 to 2 × 10 ¹⁹ cm ^−3, and the growth rate is set to 0 at least at the initial growth stage of the current diffusion layer. .5-2 μm / h, and the growth temperature of the first and second current diffusion layers is 750 ° C. or higher with respect to the growth temperature of the active layer and the cladding layer of 740 ° C. or lower. There is a proposal to manufacture a small number of LED elements (see Patent Document 1).
Japanese Patent Laid-Open No. 2002-280606

However, as described above, the surface of the epitaxial wafer produced by the conventional method, that is, the surface of the GaP current dispersion layer is a mirror surface by visual observation, but there are many surface defects (structures) when measured by microscopic observation or surf scanning. Yes. For this reason, they cause cracks and electrode peeling in the chip forming process, and the yield is greatly reduced.
In the conventional method, the growth temperature of the GaP current dispersion layer is often higher than the growth temperature of the AlGaInP quaternary layer. This is because when the growth temperature is increased, defects (structures) on the surface of the GaP layer are reduced. However, since the growth thickness of the GaP layer is thick, the growth time is very long. During this time, the quaternary layer below the p-type cladding layer is exposed to a high temperature. When the time during which the quaternary layer is exposed to a high temperature becomes longer, Zn (zinc) and Mg (magnesium), which are dopants used in the p-type cladding layer, move to the active layer by thermal diffusion. When the dopant diffuses into the active layer, problems occur in LED characteristics such as a decrease in light emission output and deterioration in long-term reliability.
In other words, in order to suppress surface defects (structures), the GaP growth temperature may be increased, but there is a trade-off relationship that when the GaP growth temperature is increased, LED characteristics deteriorate due to dopant diffusion.

  In addition, when the method of Patent Document 1 is applied to an AlGaInP-based LED using GaP as a current spreading layer, the surface of the GaP layer is exposed to much higher temperatures while the Gap layer is grown even if the surface defects of the GaP layer can be reduced. Therefore, dopant diffusion from the p-type cladding layer to the active layer occurs, causing a problem in that the light emission output is lowered and the reliability is deteriorated.

  The present invention provides an AlGaInP-based epitaxial wafer for light-emitting diodes and a method for manufacturing the same that can reduce the surface defects (structures) of the epitaxial wafer for light-emitting diodes without deteriorating the characteristics of the light-emitting diodes. It is in.

In order to solve the above problems, the present invention is configured as follows.
According to a first aspect of the present invention, at least an n-type (Al _x1 Ga _1-x1 ) _y1 In _1-y1 P clad layer and (Al _x2 ) are formed on a conductive substrate using metal organic vapor phase epitaxy. A Ga1 _-x2 ) _{y2In1 -y2P} active layer, a p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer, and a current-spreading layer made of GaP are stacked. In the method for producing an AlGaInP-based epitaxial wafer for light emitting diodes, the growth temperature of the GaP layer at the initial stage of growth is set to the p-type (Al _x3 Ga _1-x3 ) _y3 In _1-y3 P when the current spreading layer made of GaP is grown. The growth is performed at a temperature higher than the growth temperature of the cladding layer, and then the remaining GaP layer is the same as the growth temperature of the p-type (Al _x3 Ga _1-x3 ) _y3 In _1-y3 P cladding layer. It is a method for producing an epitaxial wafer for an AlGaInP-based light-emitting diode, characterized by growing at an equal temperature or lower temperature.

A second aspect of the present invention, in a first aspect, wherein the growth temperature of the p-type _{(Al x3 Ga 1-x3)} y3 In 1-y3 P cladding layer is in the range of 600 to 650 ° C. This is a method for manufacturing an AlGaInP-based light-emitting diode epitaxial wafer.

  According to a third aspect of the present invention, in the first aspect or the second aspect, the growth temperature of the GaP layer in the initial stage of growth is 750 to 900 ° C. An AlGaInP-based epitaxial wafer for light-emitting diodes This is a manufacturing method.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the thickness of the GaP layer in the initial stage of growth is 100 to 500 nm. It is a manufacturing method of an epitaxial wafer.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the growth temperature of the remaining GaP layer is 550 to 650 ° C. This is a method for producing an AlGaInP-based light-emitting diode epitaxial wafer according to any one of the above.

In a sixth aspect of the present invention, at least an n-type (Al _x1 Ga _1-x1 ) _y1 In _1-y1 P cladding layer and (Al _x2 Ga _1-x2 ) _y2 In _1-y2 are formed on a conductive substrate. In an epitaxial wafer for an AlGaInP light emitting diode comprising a P active layer, a light emitting layer made of a p-type (Al _x3 Ga _1-x3 ) _y3 In _1-y3 P cladding layer, and a current spreading layer made of GaP, A current spreading layer made of GaP having a thickness of 100 to 500 nm and grown at a temperature higher than the growth temperature of the p-type (Al _x3 Ga _1-x3 ) _y3 In _1-y3 P cladding layer; AlGa, characterized in that it consists of a p-type _{(Al x3 Ga 1-x3)} y3 in 1-y3 P cladding layer GaP layer grown at a temperature lower than the growth temperature and or equivalent It is an epitaxial wafer for an InP-based light emitting diode.

  According to the present invention, since the GaP current distribution layer is grown in two stages of initial high-temperature growth and low-temperature growth, defects on the surface of the GaP current distribution layer can be greatly reduced, and the light emitting diode with good surface flatness An epitaxial wafer is obtained. Since the GaP surface defects are greatly reduced, cracks and electrode peeling due to surface defects can be prevented during the chip forming process, and the yield can be improved. Further, since the initial high-temperature growth is GaP growth at a low temperature, dopant diffusion into the active layer is suppressed, and long-term reliability is improved.

Embodiments of an AlGaInP-based light-emitting diode epitaxial wafer and a method for manufacturing the same according to the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic layer structure of an AlGaInP-based light emitting diode epitaxial wafer of this embodiment. As shown in FIG. 1, this epitaxial wafer for light-emitting diodes includes a buffer layer 2, an n-type ( _{Alx1Ga1 -x1} ) _{y1In1 -y1P} cladding layer 3, and an (Al _{x2Ga1 -x2} ) _{y2In1 -y2P} active layer 4, p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer 5, light-emitting layer, and p-type GaP layer current distribution Layer 6. The current spreading layer 6 includes a high-temperature grown GaP underlayer 6a having a thickness of 100 to 500 nm and a low-temperature grown GaP layer 6b.

This light-emitting diode epitaxial wafer is manufactured using the MOVPE method. The conductive substrate 1 is installed in the MOVPE apparatus, and the necessary III source gas, group V source gas, carrier gas and dopant source gas are supplied onto the conductive substrate 1 heated by the heater, and the buffer layer 2 N-type (Al _x1 Ga _1-x1 ) _y1 In _{1 -y1} P cladding layer 3, (Al _x2 Ga _1-x2 ) _y2 In _{1 -y2} P active layer 4, and p-type (Al _x3 Ga _{1 -1} ) _x3 ) _y3 In _1-y3 P cladding layer 5, high-temperature grown GaP underlayer 6 a, and low-temperature grown GaP layer 6 b are sequentially epitaxially grown. Zn, Mg, C, etc. are used for the p-type dopant, and Se, Si, Te, etc. are used for the n-type dopant.

In the growth of the current spreading layer 6 made of GaP, the growth temperature of the high temperature growth GaP underlayer 6a at the initial _stage of growth is higher than the growth temperature of the p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer 5. Then, the remaining low-temperature grown GaP layer 6b is grown at a temperature equal to or lower than the growth temperature of the p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer 5. More specifically, the growth temperature in the MOVPE growth includes n-type (Al _x1 Ga _1-x1 ) _y1 In _{1 -y1} P cladding layer 3, (Al _x2 Ga _{1 -x2} ) _y2 In _{1 -y2} P active layer. 4 and p-type (Al _x3 Ga _1-x3 ) _y3 In _1-y3 P cladding layer 5 is set to 600 to 650 ° C., high temperature growth GaP underlayer 6 a is 750 to 900 ° C., and low temperature growth GaP layer 6 b is 550 to 650 ° C. It is preferable to grow at.

In this embodiment, after the growth of the n-type cladding layer 3, the active layer 4, and the p-type cladding layer 5 which are AlGaInP quaternary layers, the initial GaP layer (thickness: 100 to 500 nm) when performing GaP growth is started from 750 ° C. The GaP layer is grown at a high temperature of 900 ° C. and then changed to a low growth temperature equal to or lower than the growth temperature of the AlGaInP quaternary layer. The intention of growing the GaP layer growth temperature in two stages of high temperature and low temperature is that the surface defects can be reduced by growing the GaP layer at a high temperature. A base layer 6a) is grown, and then a GaP layer (low temperature growth GaP layer 6b) is grown at a temperature equal to or lower than the growth temperature of the AlGaInP quaternary layer in order to suppress dopant diffusion into the active layer 4. Since the surface defects of the GaP layer are generated due to lattice mismatch between the AlGaInP quaternary layer and the GaP layer, it is considered that the surface defects are generated from the initial growth stage of the GaP layer. Therefore, if a clean GaP layer (high temperature growth GaP underlayer 6a) with few defects can be grown at the initial growth stage of the GaP layer, the clean GaP layer is succeeded even if the growth temperature is lowered thereafter. If growth is possible at a low temperature, the diffusion of the dopant into the active layer 4 can be suppressed, and the deterioration of the LED characteristics can also be suppressed.
In this way, by growing in the two-stage temperature profile of high temperature at the initial stage of growth and then low temperature, surface defects of the current spreading layer 6 made of GaP are reduced, and diffusion of the dopant can be suppressed, so that the LED characteristics are deteriorated. Is also suppressed.

The reason why the growth temperature of the high-temperature growth GaP underlayer 6a at the initial stage of growth is 750 ° C. to 900 ° C. is that the amount of surface defects (structures) generated is large at 750 ° C. This is because the surface defects are reduced as described above, but conversely, GaP re-evaporation occurs and the flatness of the surface is impaired (the surface becomes cloudy).
The reason why the thickness of the high-temperature grown GaP underlayer 6a grown at a high temperature is 100 to 500 nm is that the thickness of 100 nm or less is not sufficient to take over a beautiful crystal with few surface defects. This is because if the thickness is 500 nm or more, the time during which the AlGaInP quaternary layer is exposed to a high temperature becomes long, so that diffusion of the dopant into the active layer occurs.
Furthermore, the reason why the growth temperature of the low-temperature grown GaP layer 6b is set to 550 to 650 ° C. is that the surface state of the GaP layer is deteriorated when the growth temperature is lower than 550 ° C., and the substrate is a GaP layer (high temperature grown GaP layer) at 550 to 650 ° C. This is because the underlying layer 6a) does not cause surface defects due to lattice mismatch, and the dopant diffusion does not proceed because it is lower than the growth temperature of the AlGaInP quaternary layer. Therefore, when the growth temperature of the low-temperature grown GaP layer 6b is 550 to 650 ° C., the diffusion of the dopant into the active layer 4 can be prevented while maintaining the flatness of the GaP surface.

  In the above embodiment, for example, a light reflection layer such as a distributed Bragg reflection film is provided between the buffer layer 2 and the n-type cladding layer 3 or in place of the buffer layer 2, or the p-type cladding layer 5 is provided. For example, a p-type intervening layer made of AlGaInP is provided to reduce the potential barrier at the heterointerface having a smaller band gap than the p-type cladding layer 5 and between the high-temperature grown GaP underlayer 6a. It can be changed.

  Next, examples of the present invention will be described. The AlGaInP-based LED epitaxial wafer of this example has the same layer structure as the LED epitaxial wafer of the above-described embodiment shown in FIG. 1, and this example will be described with reference to FIG.

  As shown in FIG. 1, the AlGaInP-based LED epitaxial wafer of this example is composed of an n-type GaAs buffer layer 2, an n-type AlGaInP cladding layer 3 and an undoped AlGaInP on a Si-doped n-type GaAs substrate 1. It has an active layer 4, a p-type AlGaInP cladding layer 5, and a current spreading layer 6 comprising a high-temperature grown GaP underlayer 6a and a low-temperature grown GaP layer 6b.

This epitaxial wafer for LED was produced using the MOVPE method. The n-type GaAs substrate 1 is heated with a heater, and hydrogen is used as a carrier gas therefor, so that the group III source materials TMG, TMA, TMI, the group V source material AsH ₃ , PH ₃ , and the dopant H ₂ Se ( Hydrogen selenide) and DEZ (diethyl zinc) were supplied as needed for growth.

On an n-type GaAs substrate 1 heated to 650 ° C., an Se-doped n-type GaAs buffer layer (thickness 200 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 2, an Se-doped n-type AlGaInP cladding layer (thickness 400 nm). , Carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 3, undoped AlGaInP active layer (thickness 500 nm) 4, Zn-doped p-type AlGaInP cladding layer (thickness 500 nm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) 5 The layers were grown in order. Next, the growth temperature is raised to 750 ° C. to grow a Zn-doped high-temperature growth GaP underlayer (thickness 200 nm, carrier concentration 5 × 10 ¹⁸ cm ⁻³ ) 6a, and then the growth temperature is lowered to 650 ° C. Then, the remaining Zn-doped low-temperature grown GaP layer (thickness 9.8 μm, carrier concentration 5 × 10 ¹⁸ cm ⁻³ ) 6b was grown.

Further, as a comparative example for comparison with the example, an LED epitaxial wafer having a structure shown in FIG. 2 was produced. In the fabrication of the epitaxial wafer for LED of the comparative example, the growth from the n-type GaAs buffer layer 2 to the p-type AlGaInP clad layer 5 was grown on the n-type GaAs substrate 1 in the same manner as the growth method of the above embodiment. For the growth of a certain GaP layer, a Zn-doped GaP current dispersion layer (thickness 10 μm, carrier concentration 5 × 10 ¹⁸ cm ⁻³ ) 7 was grown at a growth temperature of 700 ° C.

The surface of the grown epitaxial wafer for LED was a mirror surface visually in both Examples and Comparative Examples. However, when observed under a microscope, there are many surface defects (structures) in the LED epitaxial wafer of the comparative example, and the surface defects (structures) are significantly larger in the LED epitaxial wafer of the example than in the comparative example. There were few. Further, when the surf scan was measured, the number of surface defects (structures) having a diameter of 5 to 50 μm was 251 / cm ² in the comparative example, but 7 / cm ² in the example.

  A chip-forming process was performed on the LED epitaxial wafers of the above examples and comparative examples to produce LED chips having a chip size of 300 μm square, and the reliability of the light emission output was evaluated. In the reliability evaluation test, 50 mA continuous energization was performed at room temperature. In the evaluation, the light emission output was measured every 24 hours, and the output change rate (relative output) with the initial characteristics was measured. FIG. 3 shows the result of the reliability evaluation test. As shown in FIG. 3, the output of the LED chip manufactured from the comparative example decreases with time, but the LED chip manufactured from the example shows almost no decrease.

It is a cross-sectional schematic diagram of the epitaxial wafer for light emitting diodes which concerns on embodiment and Example of this invention. It is a cross-sectional schematic diagram of the epitaxial wafer for light emitting diodes of a comparative example. It is the graph which showed the relative output in the long-term reliability test of the LED chip produced using the epitaxial wafer for light emitting diodes of an Example and a comparative example.

Explanation of symbols

1 Conductive substrate (n-type GaAs substrate)
2 Buffer layer (n-type GaAs buffer layer)
3 n-type (Al _x1 Ga _1-x1 ) _y1 In _1-y1 P cladding layer 4 (Al _x2 Ga _1-x2 ) _y2 In _1-y2 P active layer 5 p-type (Al _x3 Ga _1-x3 ) _y3 In _{1 -Y3} P clad layer 6 current spreading layer (GaP current spreading layer)
6a High temperature growth GaP underlayer 6b Low temperature growth GaP layer 7 GaP current distribution layer

Claims (6)

By metal-organic vapor phase epitaxy on a conductive substrate, at least an n-type _{(Al x1 Ga 1-x1)} y1 In 1-y1 P cladding _{layer, (Al x2 Ga 1-x2} ) y2 In 1- _y2 and P active layer, p-type _{(Al x3 Ga 1-x3)} y3 in 1-y3 P and light emitting layer made of the cladding layer, an AlGaInP light emitting diode epitaxial wafer for laminating forming the current spreading layer made of GaP In the production method,
When growing the current spreading layer made of GaP, the growth temperature of the GaP layer in the initial _stage of growth is higher than the growth temperature of the p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer, and then The remaining GaP layer is grown at a temperature equal to or lower than the growth temperature of the p-type ( _{Alx3Ga1 -x3} ) _{y3In1 -y3P} cladding layer, and is epitaxially grown for an AlGaInP-based light emitting diode. Wafer fabrication method. The growth temperature of the p-type _{(Al x3 Ga 1-x3)} y3 In 1-y3 P cladding layer, the light emitting diode epitaxial of AlGaInP system according to claim 1, characterized in that in the range of 600 to 650 ° C. Wafer fabrication method.   3. The method for producing an epitaxial wafer for an AlGaInP-based light emitting diode according to claim 1, wherein a growth temperature of the GaP layer in the initial stage of growth is 750 to 900 ° C. 3.   The method for producing an epitaxial wafer for an AlGaInP-based light-emitting diode according to any one of claims 1 to 3, wherein a thickness of the GaP layer in the initial stage of growth is 100 to 500 nm.   The growth temperature of the remaining GaP layer is 550 to 650 ° C, The method for producing an AlGaInP-based epitaxial wafer for light-emitting diodes according to any one of claims 1 to 4. On the conductive substrate, at least an n-type ( _{Alx1Ga1 -x1} ) _{y1In1 -y1P} cladding layer, an ( _{Alx2Ga1 -x2} ) _{y2In1 -y2P} active layer, and a p-type (Al _x3 Ga _1-x3 ) _y3 In _{1- y3} In an epitaxial wafer for an AlGaInP-based light emitting diode comprising a light emitting layer made of a P cladding layer and a current spreading layer made of GaP,
Current spreading layer made of the GaP is a GaP base layer grown at a temperature higher than the growth temperature of a thickness 100~500nm the p-type _{(Al x3 Ga 1-x3)} y3 In 1-y3 P cladding layer, An epitaxial wafer for an AlGaInP-based light emitting diode, comprising a GaP layer grown at a temperature equal to or lower than a growth temperature of the p-type (Al _x3 Ga _1-x3 ) _y3 In _{1 -y3} P cladding layer.