| As a Ⅲ-Ⅴ group direct band-gap semiconductor material, GaN has a wide band-gap (3.39eV) at room temperature. In the1990s, the first double heterostructure InGaN/AlGaN blue LED was developed by a Japanese company Nichia Corporation, which marked GaN had bec ame a third generation of semiconductor materials after Si and GaAs and boarded the commer cialization stage. Because of the excellent characteristics, GaN has been applied to many field s, such as light emitting diode (LED), laser diode (LD), UV detectors, solar cells, large-scale i ntegrated circuits and so on. Also, it will have a wide application prospect in the fields of high frequency, high temperature, anti-radiation and high-power semiconductor device. For the fa brication of GaN thin film materials, substrate materials such as sapphire (α-Al2O3), Si, SiC, a nd quartzs are commonly used, and it already has a relatively mature preparation technique. A11kinds of substrate materials has its unique advantages, but there are still many shortcomings, like there is a large crystal lattice distortions between sapphire/Si and GaN, the price of SiC i s expensive.In order to weaken the substrate material impact on the development of GaN and make the best use of material characteristic, in recent years, people began to try to deposit GaN film on metal substrate. First of all, metal has a good thermal conductivity which can effectively solve the problem of heat dissipation in the LED devices; secondly, conductive metal can be directly used as a device electrode; finally, cheap metal substrate can save the cost. However, to deposit GaN films on metal substrate, several problems must overcome. First, metal can be different degrees melted in a higher growth temperature, second, harmful interfacial reaction between metal and GaN will happen in high temperature, or exacerbates the diffusion of the metal impurities to the GaN film which will affect the quality of the film; third, there is a high thermal expansion coefficient difference between GaN and metal material which will cause the interface stress increases in high-temperature growth process and can easily cause film cracking.To solve the above-mentioned problems, in this article, silver-plated silicon which has high reflectance is used as substrate to reduce the light absorption of metal substrate. Electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) is used to avoid melting the substrate at high temperature, in the meantime, before deposition, buffer layer was deposited in order to reduce the lattice mismatch between the substrate and GaN films, and finally high-quality GaN film was successfully prepared. In the Experiment, TMGa and nitrogen are used as the sources of Ga and N respectively, and ultra-pure hydrogen is used as a carrier gas. The effect of TMGa flux and deposition temperature on the as-grown GaN films is systematically investigated by in-situ reflection high energy electron diffraction(RHEED), X-ray diffraction(XRD), atomic force microscopy (AFM), scanning electron microscope(SEM) and semiconductor tester. The results showed that:that high-quality GaN films with high preferred orientation and smooth surface were successfully achieved on Ag at the proper deposition temperature of485℃and TMGa flux of1.2seem. |
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