| In recent years, Gallium Nitride as a wide band gap semiconductor has attracted more and more attention and advanced rapidly, mainly due to its promising applications in short-wave light-emitting devices, photodetectors, as well as anti-radiation, high frequency and high power electronic devices. However, it is difficult to grow large bulk single crystal of GaN, heteroepitaxy on various substrates is so far necessary for the growth of GaN films and the development of GaN-based devices. Almost all high quality GaN films are grown on sapphire, but sapphire itself is not conductive, hard to cleave and expensive. Accordingly, Si is regarded as one of the most promising substrate for growing the GaN film due to its large size, high quality and relatively low cost. Furthermore, the GaN epitaxy on Si will facilitate the integration of microelectronics and optoelectronics. Therefore, the investigation of GaN epitaxy on silicon is of extreme practical importance. However, there are several difficulties to grow single crystalline GaN films directly on the Si substrate 1) the high lattices mismatch (17%) and the differences in the thermal expansion coefficient (100%) between GaN (in wurtzite structure) and Si; 2) the poor wetting of GaN on Si; 3) the nitridation of the Si surface during growth of nitrides. To overcome these impediment, two-step method are used extensively: a buffer layer is firstly grown between the Si substrate and the GaN film, then GaN epilayer is grown on it. Results indicate that the quality of the film increased remarkably by using buffer layer, and some new phenomena will appear.phenomena will appear.In this paper, we chose a -Al2O3 material on Si to replace the sapphire substrates for growth of GaN because it can firstly overcome the above three impediments, and a -Al2O3 may serve as an insulator layer between the GaN and the Si. In particular, epitaxial growth of insulator layers on Si is of great importance in achieving Si on insulator (SOI) structures and for the long-range goal of three-dimensional integrated circuits. Furthermore, in this system the dosage of sapphire is very little so can reduce the cost. The detailed growth procedure of the film is presented. The effects of the process parameters on the properties of GaN films are discussed. The optimum thickness of the buffer layer and the optimum annealing temperature and time for the fabrication of GaN films by this method are investigated. In addition, we also studied the photoluminescence properties of GaN films and discussed the mechanism of it. In addition, it is another important side of our work to grow GaN film on Si by hot-wall Chemical Vapor Deposition and discuss the effects of the carrier and the growth time on the quality of the film(1) Two-step method is used to grow GaN films, i e, Al2O3 film which is used as buffer layer was firstly grown on Si(111) by, then Ga2O3 film was grown on it also by r.f magnetron sputtering. Secondly, the samples were annealed in a high purity ammonia ambience to fabricate GaN films by self-assembling.(2) The X-ray diffraction pattern of the target after annealing at 900 for 15 mins shows it still is Al2O3. This indicates that under this condition the Al2O3 do not reacted with the NH3, so we can confirm that the buffer layer in this method is Al2O3.(3)The structure of the films was characterized by Fourier transform infrared (FTIR) transmission spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the as-grown sampleswere hexagonal wurtzite structure GaN. The surface morphology of the samples was detected by Scanning electron microscopy (SEM). The optical properties of sample were analyzee by photoluminescence (PL).(4) The effects of the process parameters on the crystal properties the morphology of GaN films are discussed. The optimum thickness of the buffer layer and the optimum annealing temperature and time for the fabrication of GaN films by this method are investigated.The thickness of the buffer layer ha...
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