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Growth of GaN material

wallpapers News 2021-04-01
The growth of gallium nitride material is achieved by the chemical reaction between Ga and NH3 decomposed by TMGa at high temperatures. The reversible reaction equation is:
Ga+NH3=GaN+3/2H2
 
Growing GaN requires a certain growth temperature and a certain NH3 partial pressure. People usually use conventional MOCVD (including APMOCVD, LPMOCVD), plasma-enhanced MOCVD (PE-MOCVD) and electron cyclotron resonance assisted MBE. The required temperature and NH3 partial pressure decrease in order. The equipment used in this work is AP-MOCVD, the reactor is horizontal, and it has been specially designed and modified. Use domestically made high-purity TMGa and NH3 as the source program materials, DeZn as the P-type doping source, (0001) sapphire and (111) silicon as the substrate, high-frequency induction heating, and low-resistance silicon as the heating element. High-purity H2 is used as the carrier gas of the MO source. Use high-purity N2 as the regulation of the growth zone. HALL measurement, double crystal diffraction, and room temperature PL spectroscopy are used as the quality characterization of GaN. In order to grow a perfect GaN, there are two key issues. One is how to avoid the strong parasitic reaction of NH3 and TMGa so that the two reactants are more completely deposited on the sapphire and Si substrate, and the other is how to grow perfect. Single crystal. In order to achieve the first goal, a variety of airflow models and reactors of various forms were designed, and finally, a unique reactor structure was finally explored. Through the distance between the TMGa pipe of the regulator and the substrate, GaN was grown on the substrate. . At the same time, in order to ensure the quality and repeatability of GaN, a silicon base is used as a heating body to prevent the violent reaction of NH3 and graphite at high temperatures. Regarding the second question, using the conventional two-step growth method and high-temperature processed sapphire material, first grow a GaN buffer layer of about 250A0 at 550°C, and then grow a perfect GaN single crystal material at 1050°C. For the growth of GaN single crystals on Si substrates, the AlN buffer layer is first grown at 1150°C, and then GaN crystals are grown. The typical conditions for growing this material are as follows:
NH3: 3L/min
TMGa: 20μmol/minV/Ⅲ=6500
N2: 3~4L/min
H2: 2<1L/min
 
People generally use Mg as a dopant to grow P-type GaN. However, after the material is grown, high-temperature annealing at about 800° C. and in an N2 atmosphere is required to achieve P-type doping. In this experiment, Zn is used as the dopant, DeZ2n/TMGa=0.15, and the growth temperature is 950℃. The high-temperature grown GaN single crystal is cooled with the furnace. Zn has the ability of P-type doping, so when the intrinsic concentration is low, P-type doping is expected to be realized.
 
However, the Ga source used in MOCVD is TMGa, and side reactants are also generated, which are harmful to the growth of GaN films. Moreover, growth at high temperatures is good for film growth, but it is also easy to cause diffusion and phase separation of multiphase films. Nakamura and others improved the MOCVD device. They first used the TWO-FLOWMOCVD (dual beam MOCVD) technology and applied this method to do a lot of research work and achieved success. The schematic diagram of dual-beam MOCVD growth is shown in Figure 1. The reactor is composed of the main gas flow consisting of H2+NH3+TMGa, which passes through the quartz jet parallel to the substrate at a high speed, and the other route H2+N2 forms an auxiliary gas flow and sprays vertically to the surface of the substrate. The purpose is to change the main gas flow. Orientation, so that the reactant is in good contact with the surface of the substrate. The GaN film grown directly on the α-Al2O3 substrate (C side) in this way has an electron carrier concentration of 1×1018/cm3 and mobility of 200cm2/v·s, which is the best method for direct growth of gallium nitride film. 

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