阅读说明：本技术 一种复合窗口层结构AlGaInP基红光LED (AlGaInP-based red LED with composite window layer structure ) 是由 裴艳丽 费泽元 张露 王钢 于 2019-04-04 设计创作，主要内容包括：本发明提供了一种低成本、低电压和光强可靠性高的倒装AlGaInP基LED芯片及其制备方法。该LED芯片由上至下依次设置n-PAD金属电极,氧化锌基透明电极,n-AlGaInP限制层,AlGaInP多层量子阱发光层,p-AlGaInP限制层,p-GaP窗口层,p-GaP重掺接触层,氧化锌电流拓展层,键合层,衬底层,p-PAD金属电极。本发明通过氧化锌基透明电极来代替部分GaP窗口层,实现导电和出光作用,从而减少GaP窗口层的厚度。在既不破坏外延片基本结构,不影响内外量子效率的基础上,比起常规的管芯GaP窗口层MOCVD高温工艺来说,氧化锌基透明电极的MOCVD低温生长工艺不仅节省了生长成本,并减少了高温对产品的不良影响。极大地提高了芯粒的电压稳定性、芯片成品的质量良率和芯片长期使用的可靠性。(The invention provides a flip AlGaInP-based LED chip with low cost, low voltage and high light intensity reliability and a preparation method thereof. The LED chip is sequentially provided with an n-PAD metal electrode, a zinc oxide base transparent electrode, an n-AlGaInP limiting layer, an AlGaInP multi-layer quantum well light-emitting layer, a p-AlGaInP limiting layer, a p-GaP window layer, a p-GaP heavily-doped contact layer, a zinc oxide current expanding layer, a bonding layer, a substrate layer and a p-PAD metal electrode from top to bottom. The invention replaces partial GaP window layer with zinc oxide base transparent electrode to realize the functions of electric conduction and light extraction, thereby reducing the thickness of GaP window layer. Compared with the conventional tube core GaP window layer MOCVD high-temperature process, the MOCVD low-temperature growth process of the zinc oxide-based transparent electrode not only saves the growth cost, but also reduces the adverse effect of high temperature on products on the basis of not damaging the basic structure of the epitaxial wafer and not influencing the internal and external quantum efficiency. The voltage stability of the core particles, the quality yield of the finished chip products and the reliability of the long-term use of the chips are greatly improved.)

1. An AlGaInP-based red LED with a composite window layer structure is characterized in that an n-PAD metal electrode, a zinc oxide-based transparent electrode, an n-GaAs ohmic contact layer, an n-AlGaInP limiting layer, an AlGaInP multi-layer quantum well light-emitting layer, a p-AlGaInP limiting layer, a p-GaP window layer, a p-GaP remixed contact layer, a zinc oxide current expanding layer, a bonding layer, a substrate layer and a p-PAD metal electrode are sequentially arranged from top to bottom;

the AlGaInP-based red LED with the composite window layer structure is prepared by utilizing an LED epitaxial structure, wherein the LED epitaxial structure sequentially comprises a GaAs substrate layer, an n-GaAs buffer layer, an n-GaInP corrosion stop layer, an n-GaAs ohmic contact layer, an n-AlGaInP limiting layer, an AlGaInP multi-layer quantum well light-emitting layer, a p-AlGaInP limiting layer, a p-GaP window layer and a p-GaP heavily-doped contact layer.

2. The AlGaInP-based red LED of claim 1, wherein the thickness of the p-GaP window layer is 0.2um to 3 um.

3. The AlGaInP-based red LED of claim 1, wherein the zinc oxide-based transparent electrode and the zinc oxide current spreading layer are epitaxially grown by an MOCVD method at a temperature of 400-450 ℃.

4. The AlGaInP-based red LED with the composite window layer structure as recited in claim 1, wherein the zinc oxide-based transparent electrode and the zinc oxide current spreading layer are both a zinc oxide-based polycrystalline composite film with a c-axis preferred orientation structure, the refractive index is 2.0-2.5, and the zinc oxide current spreading layer has a transmittance of 95% or more for light with a wavelength of 600-640 nm.

5. The AlGaInP-based red LED as recited in claim 1, wherein the p-GaP window layer is formed by MOCVD at 650-830 ℃, the thickness of the p-GaP window layer is 0.2-5um, and the carrier concentration of the p-GaP heavily doped contact layer is 1 x 10¹⁹cm^-3～1×10²⁰cm^-3。

6. The method for preparing AlGaInP-based red LED with the composite window layer structure as recited in any one of claims 1 to 5, comprising the following steps:

s1, preparing a zinc oxide current expanding layer on a p-GaP heavily-doped contact layer of the LED epitaxial structure;

s2, sputtering metal 1 on the zinc oxide current expansion layer to serve as a bonding material, simultaneously sputtering metal 2 on a heavily doped Si substrate to serve as the bonding material, and then bonding the metal 1 and the metal 2 together by using a vacuum bonding instrument to obtain a bonding layer;

and S3, mixing hydrogen peroxide and ammonia water to form a corrosive liquid to remove the GaAs substrate layer and the n-GaAs buffer layer, and rinsing with a hydrochloric acid solution to remove the GaInP corrosion retention layer to expose the n-GaAs ohmic contact layer. Growing a zinc oxide base transparent electrode on the n-GaAs ohmic contact layer, photoetching a pattern on the zinc oxide base transparent electrode, evaporating an n-PAD metal electrode, and then performing a metal electrode stripping process;

s4, thinning the Si substrate, evaporating a p-PAD metal electrode, and cutting a corresponding tube core after alloying.

7. The method of claim 6, wherein the metal 1 and the metal 2 are both Au, or the metal 1 and the metal 2 are Au and In.

8. The method of claim 6, wherein the step of forming a zinc oxide current spreading layer on the p-GaP heavily doped contact layer of the LED epitaxial structure comprises: placing the LED epitaxial structure into an MOCVD cavity for epitaxial growth, wherein the reaction temperature is 400-; the reaction source takes diethyl zinc as a zinc source, deionized water as an oxygen source, and at least one of trimethyl aluminum, trimethyl indium and triethyl gallium as a doping source.

9. The method for fabricating AlGaInP-based red LED with composite window layer structure as claimed in claim 6, wherein the p-PAD metal electrode is AuGeNi/Ag/Au, the alloy temperature is 350-450 ℃, and the alloy time is 30-45 min.

10. The method of fabricating the AlGaInP-based red LED with composite window layer structure as claimed in claim 6, wherein the n-PAD metal electrode is Cr/Al/Ni/Au.

Technical Field

The invention belongs to the field of semiconductor light emitting diodes, and mainly relates to an AlGaInP-based red light LED with a composite window layer structure.

Background

The LED chip is currently mainly developed by a small-sized LED product with high power, high brightness and high integration, which requires that the light extraction efficiency of the LED chip is very high, so that the development of a transparent electrode (TCL) with a large critical light-emitting angle, high visible light transmittance and high reliability becomes a development trend of improving the light extraction efficiency of the LED in the future. Generally, there are three requirements for the choice of transparent electrodes: good electrical conductivity, excellent visible light transmittance and high material stability. In the production of LEDs, there are three materials that can meet the three requirements: the first is a first-generation transparent electrode represented by Ni/Au (japanese patent No. 5,686,738), which has good conductivity and material stability, but is significantly insufficient in that the maximum transmittance of visible light is less than 75%; the second generation of transparent electrode represented by Indium Tin Oxide (ITO) (patent of taiwan institute of technology, TW Pat. 102019) has good conductivity and high visible light transmittance, but has the main defects of poor reliability of the material, especially poor resistance to water vapor and hydrogen ions in the environment, and in addition, because the material contains rare metal tellurium, the electrode is toxic, not friendly to the environment and poor in sustainable development; the third one is a new generation transparent electrode represented by ZnO, which has good conductivity, extremely high visible light transmittance and extremely high material stability, is environmentally friendly and can be developed continuously, and represents the development trend of the transparent electrode of the LED chip in the future.

The light emitting layer of the conventional GaAs-based AlGaInP light emitting diode is a GaP layer, and the GaP layer also plays an important role in ohmic contact layer and current spreading. However, the low-resistance and high-transmittance GaP window layer needs to be prepared at high temperature, and the current spreading effect of the GaP window layer is poor. Foreign research reports prove that the GaP window layer needs to obtain an ideal current spreading effect, the thickness of the GaP window layer can reach 9um, the MOCVD equipment is adopted to grow the material with the thickness, the process difficulty exists, the production cost is improved, and meanwhile, the excessively thick GaP window layer brings adverse effects on the reliability of the device. Compared with a GaP layer, the zinc oxide-based transparent electrode has good lateral current expansibility, and has the advantages of high transmittance, good conductivity, wear resistance and the like, and good ohmic contact with the GaP layer. Therefore, the zinc oxide based transparent electrode can be used for replacing partial GaP layer to be used as a window layer of an LED chip, thereby reducing the thickness of the window layer and being used as a transparent electrode material for improving the brightness of the AlGaInP based chip.

Disclosure of Invention

Aiming at the defects that the cost of the chip is increased due to the fact that the thickness of a GaP window layer of the existing AlGaInP-based LED chip is too thick, photons can be absorbed due to the fact that the GaP window layer is too thick in a flip-chip structure, the light emitting efficiency of the LED chip is reduced and the like, the invention aims to provide the flip-chip AlGaInP-based LED chip with low cost, low voltage and high light intensity reliability and the preparation method thereof.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

an AlGaInP-based red LED with a composite window layer structure comprises an n-PAD metal electrode, a zinc oxide-based transparent electrode, an n-GaAs ohmic contact layer, an n-AlGaInP limiting layer, an AlGaInP multi-layer quantum well light-emitting layer, a p-AlGaInP limiting layer, a p-GaP window layer, a p-GaP heavily-doped contact layer, a zinc oxide current expanding layer, a bonding layer, a substrate layer and a p-PAD metal electrode from top to bottom in sequence;

the AlGaInP-based red LED with the composite window layer structure is prepared by utilizing an LED epitaxial structure, wherein the LED epitaxial structure sequentially comprises a GaAs substrate layer, an n-GaAs buffer layer, an n-GaInP corrosion stop layer, an n-GaAs ohmic contact layer, an n-AlGaInP limiting layer, an AlGaInP multi-layer quantum well light-emitting layer, a p-AlGaInP limiting layer, a p-GaP window layer and a p-GaP heavily-doped contact layer.

The LED epitaxial structure is prepared by a conventional preparation method in the field.

According to the invention, the zinc oxide-based transparent electrode replaces part of the p-GaP window layer to realize the conduction effect according to the properties of high transmittance and low resistivity of the zinc oxide-based transparent electrode, so that the thickness of the p-GaP window layer is reduced. Compared with the conventional tube core GaP window layer MOCVD high-temperature process, the MOCVD low-temperature growth process of the zinc oxide-based transparent electrode not only saves the growth cost, but also reduces the adverse effect of high temperature on products on the basis of not damaging the basic structure of the epitaxial wafer and not influencing the internal and external quantum efficiency. The invention greatly improves the voltage stability of the core particles, the quality yield of the finished chip products and the reliability of the long-term use of the chip.

Preferably, the thickness of the p-GaP window layer is 0.2um-5 um.

Preferably, the zinc oxide-based transparent electrode and the zinc oxide current expansion layer are epitaxially grown by an MOCVD method at the growth temperature of 400-450 ℃.

Preferably, the zinc oxide-based transparent electrode and the zinc oxide current spreading layer are polycrystalline composite films with a sphalerite structure with c-axis preferred orientation, the refractive index is between 2.0 and 2.5, and the zinc oxide-based transparent electrode and the zinc oxide current spreading layer have a transmittance of more than 95% for light with a wavelength of 600-640 nm.

Preferably, the p-GaP window layer is prepared by MOCVD method at 830 deg.C and 650-¹⁹cm^-3～1×10²⁰cm^-3。

The preparation method of the AlGaInP-based red LED with the composite window layer structure comprises the following steps:

s1, preparing a zinc oxide current expanding layer on a p-GaP heavily-doped contact layer of the LED epitaxial structure;

s2, sputtering metal 1 on the zinc oxide current expansion layer to serve as a bonding material, simultaneously sputtering metal 2 on a heavily doped Si substrate to serve as the bonding material, and then bonding the metal 1 and the metal 2 together by using a vacuum bonding instrument to obtain a bonding layer;

s3, mixing hydrogen peroxide and ammonia water to form a corrosive liquid to remove the GaAs substrate layer and the n-GaAs buffer layer, rinsing the corrosive liquid by using a hydrochloric acid solution to remove the GaInP corrosion retention layer to expose the n-GaAs ohmic contact layer, growing a zinc oxide-based transparent electrode on the n-GaAs ohmic contact layer, photoetching patterns on the zinc oxide-based transparent electrode, evaporating an n-PAD metal electrode, and then performing a metal electrode stripping process;

s4, thinning the Si substrate, evaporating a p-PAD metal electrode, and cutting a corresponding tube core after alloying.

Preferably, the metal 1 and the metal 2 are both Au, or the metal 1 and the metal 2 are Au and In.

The method for preparing the zinc oxide current expanding layer on the p-GaP heavily-doped contact layer of the LED epitaxial structure comprises the following steps: placing the LED epitaxial structure into an MOCVD cavity for epitaxial growth, wherein the reaction temperature is 400-; the reaction source takes diethyl zinc as a zinc source, deionized water as an oxygen source, and at least one of trimethyl aluminum, trimethyl indium and triethyl gallium as a doping source.

Preferably, the p-PAD metal electrode is AuGeNi/Ag/Au, the alloy temperature is 350-450 ℃, and the alloy time is 30-45 min.

Preferably, the n-PAD metal electrode is Cr/Al/Ni/Au.

The invention has the beneficial effects that:

1) a zinc oxide-based transparent electrode with high transmission and low resistance is epitaxially grown on the surface of the p-GaP window layer by adopting the MOCVD technology to serve as a current extension layer to replace part of the function of the p-GaP window layer, so that the whole thickness of the window layer is reduced. The thickness of the p-GaP window layer is reduced, so that the number of absorbed photons in the p-GaP window layer can be reduced when photons are reflected to the light emitting layer from the bonding layer, and the light emitting efficiency is improved.

2) The MOCVD epitaxial temperature of the zinc oxide transparent electrode is low, the temperature range is 400-450 ℃, and the growth cost is greatly reduced compared with that of an AlGaInP-based LED with a single-layer p-GaP window layer structure.

3) MOCVD epitaxial growth of zinc oxide transparent electrodes with inexpensive water (H)₂O) is taken as an oxygen source, diethyl zinc (DEZn) is taken as a Zn source material, and at least one of trimethyl aluminum (TMAl), trimethyl indium (TMIn) and triethyl gallium (TEGa) is taken as a doping source, so that the preparation method is suitable for low-cost and large-area production and popularization.

4) The AlGaInP-based red LED chip with the flip-chip structure has high reliability, low forward working voltage and high light extraction efficiency, and provides an effective method and a way for realizing the high-efficiency and low-cost AlGaInP-based LED chip.

Drawings

FIG. 1 is a schematic diagram of an AlGaInP-based red LED chip structure with a composite window layer structure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of the present invention is not limited to the embodiments.