CN104332532A - Method for manufacturing high-luminous-efficiency light-emitting diode - Google Patents

Abstract

The purpose of the present invention is to provide a method for manufacturing a high-efficiency light-emitting diode. ITO is used as a transparent conductive film for LEDs. In order to reduce the light absorption of ITO to the LED quantum well, the thickness of the ITO film is reduced to 1200 The ITO film is prepared in two steps: the first step is to evaporate the first layer of ITO with a thickness of 500 Next, high temperature annealing in the annealing furnace forms a good ohmic contact with P-GaN; the second step is to continue evaporating the second layer of ITO with a thickness of 700 The film layer is not annealed. Compared with the ITO film prepared by the conventional process, the transmittance of the ITO film prepared by the method of the present invention is not reduced, but due to the reduced light absorption of the quantum well, the light power of the prepared LED high-power chip is increased by more than 5% compared with the conventional process, and the operating voltage is not significantly increased. Therefore, the light efficiency of the LED high-power chip is finally improved by more than 3%.

Description

A method of manufacturing a high-efficiency light-emitting diode

technical field

The invention relates to the field of photoelectric devices, in particular to a method for manufacturing a high-efficiency light-emitting diode.

Background technique

A light emitting diode (LED) is a junction electroluminescent semiconductor device that converts electrical signals into optical signals. Compared with other traditional light sources, high-performance LEDs have significant advantages such as high photoelectric conversion efficiency, long life, low loss, and no pollution. Therefore, it is energy-saving, A very important option to reduce carbon emissions.

Usually, indium tin oxide (ITO) is used as the P-side transparent electrode in the process of preparing LED chips. ITO has a low sheet resistance and has good current spreading effect. After ITO is annealed, it can form a good ohmic contact with P-GaN, which can reduce the working voltage of 45mil high-power LED chip to below 3.5v (350mA). In addition, the ITO conductive film itself has a high transmittance and a refractive index (n=1.9) between GaN (n=2.5) and air (n=1), which can extract most of the light inside the GaN material.

ITO transparent conductive film is usually prepared by electron beam evaporation in a single cycle thickness, the transmittance before annealing is about 90%, and the square resistance is 30-40Ω/□. Usually, the ITO film needs to be annealed at high temperature (500 degrees) to form a good ohmic contact with P-GaN. However, high-temperature annealing increases the crystallization degree of ITO, and the more stable the peripheral electrons are, the higher the square resistance of the film is. In addition, the ITO is usually annealed in a furnace tube under a nitrogen atmosphere, and the residual oxygen in the chamber will further supplement the ITO with oxygen, which will also increase the square resistance of the ITO. Therefore, although the transmittance of ITO increases by about 5% after annealing, the square resistance can increase to 40-60Ω/□.

If you want to obtain high-efficiency LED chips, it is required that the ITO transparent conductive film has higher transmittance, smaller square resistance, and smaller absorption of light emitted by LED quantum wells. Therefore, the brightness of LED chips will be further improved and the operating voltage will be further reduced. If the thickness of the ITO film is reduced, the brightness of the LED chip will increase due to the reduction of the light absorption of the ITO film to the LED quantum well, but the reduction in the thickness of the ITO will greatly increase the square resistance, and the annealing will increase the square resistance of the ITO. In the end, the voltage of the LED chip will also increase, and the light efficiency will not be significantly improved.

Contents of the invention

The object of the present invention is to provide a method for manufacturing a high-efficiency light-emitting diode. ITO is used as the LED transparent conductive film. In order to reduce the light absorption of ITO to the LED quantum well and improve the brightness of the LED, the thickness of the ITO film is reduced to the following. Due to the reduction of the thickness of the ITO film and the increase of the square resistance of the ITO due to the annealing process, the voltage of the LED will eventually increase. In order to alleviate this effect, the present invention proposes that the ITO film is prepared in two steps: the first step is to evaporate the first layer of ITO, thickness Next, high-temperature annealing in the annealing furnace forms a good ohmic contact with P-GaN. In the second step, continue to vapor-deposit the second layer of ITO on the first layer of ITO after annealing, with a thickness of Left and right, this film layer is not annealed to prevent the increase of LED square resistance and operating voltage due to annealing crystallization and oxygen supplementation.

Compared with the ITO film prepared by the conventional process, the transmittance of the ITO film prepared by the method of the present invention is not significantly reduced, but due to the reduced light absorption of the quantum well, the optical power of the prepared LED high-power chip is increased by 5% compared with the conventional process. above. Compared with the ITO film prepared by the conventional process, the square resistance of the ITO film prepared by the method of the present invention is not significantly increased, the ohmic contact is good, and the working voltage of the prepared LED high-power chip is not significantly increased compared with the conventional process. Therefore, the light efficiency of the final LED high-power chip is increased by more than 3%.

Description of drawings

In order to further illustrate the specific technical content of the present invention, below in conjunction with embodiment and accompanying drawing detailed description as follows, wherein:

Fig. 1 is a schematic structural diagram of a conventional process LED.

Fig. 2 is a schematic diagram of the LED structure of the process of the present invention.

Fig. 3 is conventional process and process 1V curve comparison figure of the present invention. The conventional process ITO thickness is Annealed at a high temperature of 500 degrees. The total thickness of ITO in the process of the present invention forward After annealing at a high temperature of 500 degrees, after Not annealed. The operating voltage of the LED45mil high-power chip adopting the technology of the invention is only 0.06V higher than that of the conventional technology LED under the working current of 350mA.

Fig. 4 is a comparison chart of the PI curves of the conventional process and the process of the present invention. The conventional process ITO thickness is Annealed at a high temperature of 500 degrees. The total thickness of ITO in the process of the present invention forward After annealing at a high temperature of 500 degrees, after Not annealed. The optical power of the LED45mil high-power chip adopting the technology of the invention is 6% higher than that of the conventional technology LED under the working current of 350mA.

Detailed ways

Please refer to Fig. 2 (schematic diagram of LED structure of the present invention), the present invention provides a method for manufacturing a high-efficiency light-emitting diode, comprising the following steps:

Step 1: Using metal-organic chemical vapor deposition (MOCVD), sequentially grow a 1 μm low-temperature GaN buffer layer 2, a 1 μm undoped GaN layer 3, a 3 μm N-GaN layer 4, and a 150 nm multi-quantum well light-emitting layer on a sapphire substrate 1 5 and 300nm P-GaN layer 6 to form a GaN epitaxial wafer;

Step 2: Prepare the GaN epitaxial wafer by photolithographic patterning, use AZ4620 photoresist as a mask, and perform ICP etching on one side of the GaN epitaxial wafer to remove P-GaN, quantum wells and part of N-GaN on one side, A mesa 41 is formed, and the etching depth of the mesa 41 is 700nm˜1500nm. Use Cl ₂ , BCl ₃ , Ar ₂ as etching gas, wherein the flow rate of Cl ₂ is 30-100 sccm, the flow rate of BCl ₃ is 10-20 sccm, the flow rate of Ar ₂ is 15-25 sccm, the etching power is 400-700W, and the RF power is 100-200W; etching time is 10-15min.

Step 3: Evaporate the first layer of ITO film 7 on the upper surface of the GaN epitaxial wafer by electron beam evaporation, with a thickness of The chamber temperature is 210 degrees, and the oxygen flow rate is 8 sccm. Take out the substrate from the electron beam evaporation station, put the substrate into the annealing furnace for annealing. The annealing atmosphere is nitrogen, the temperature is 500 degrees, and the time is 20 minutes. The first layer of ITO film 7 forms a good ohmic contact with P-GaN through high temperature annealing, which reduces the contact voltage;

Step 4: put the annealed substrate into the electron beam evaporation table to evaporate the second layer of ITO film 8, the thickness The chamber temperature is 210 degrees, and the oxygen flow rate is 8 sccm. The second layer of ITO thin film 8 does not need to be annealed, avoiding the crystallization caused by high-temperature annealing and the increase of LED square resistance caused by oxygen supplementation, which will eventually increase the LED operating voltage;

Step 5: Select AZ6130 photoresist and aqua regia (3HCl: HNO ₃ ) to etch out the ITO pattern by photolithography, remove the ITO films 7 and 8 on the side walls of the P-GaN6 and the multiple quantum wells 5, and remove the ITO on the mesa 41 Thin films 7 and 8 form ITO transparent electrodes on the P-type mesa.

Step 6: On the P-GaN layer 6, the ITO layer 8 and the N-GaN layer 41, select the negative photoresist L-300 to photoetch the P and N electrodes, and use the electron beam evaporation method to evaporate metal CrPtAu The P electrode 9 and the N electrode 10 are formed after peeling. The thickness of the P and N electrode metals is relatively thick, which is convenient for wiring testing when packaging chips;

Step 7: Thin the sapphire substrate of the chip to 150um, split it into individual chips, and conduct the V-I characteristic test and P-I characteristic test of the device.

Claims (4)

1. A method for making a high-efficiency light-emitting diode, comprising the steps of: Step 1: Using the metal organic chemical vapor deposition (MOCVD) method, the low-temperature GaN buffer layer 2, the undoped GaN layer 3, the N-GaN layer 4, the multi-quantum well light-emitting layer 5 and the P -GaN layer 6, forming a GaN epitaxial wafer; Step 2: Etching one side of the GaN epitaxial wafer to form a mesa 41; Step 3: Evaporate the first layer of ITO film 7 on the upper surface of the GaN epitaxial wafer, and anneal the first layer of ITO film 7 in an annealing furnace; Step 4: Evaporate a second layer of ITO film 8 on the first layer of ITO film 7 after annealing, without annealing; Step 5: Perform photolithography and etching processes on the first layer of ITO film 7 and the second layer of ITO film 8, and form ITO transparent electrodes on the P-type mesa; Step 6: making a P electrode on the second layer of ITO thin film 8 and making an N electrode on the mesa 41 to complete the device preparation. the 2. The manufacturing method of a high-efficiency light-emitting diode according to claim 1, wherein the semiconductor substrate 1 is sapphire, silicon, silicon carbide or metal. the 3. the manufacture method of a kind of high light-efficiency light-emitting diode according to claim 1, wherein the thickness of first layer ITO thin film 7 is The thickness of the second layer of ITO film 8 is . 4 . The method for manufacturing a high-efficiency light-emitting diode according to claim 1 , wherein the etching depth of the mesa 41 reaches into the N-GaN layer 4 . the