Iii-n Materials, Rf, The Plasma Mbe, Growth And Physical Research

This dissertation mainly focused on 111-N materials and physics. The work commenced from building the RF plasma MBE system and aimed at AIGaN/GaN heterostructure high temperature, high electron mobility transistor. Up to now, we have achieved such results as follows: 1. As a main member, I participated in setting up the RE plasma MBE system and UV-visible monochrometer spectra system. Using one year, we successfully transformed the homemade IV MBE into the RE Plasma MBE. 2. GaN was grown on sapphire substrate by RF plasma MBE. In order to suppress the large lattice mismatch and thermal coefficient mismatch, Ga polish, high temperature nitridation and low temperature buffer layer were necessary. Growth parameters were optimized one by one and an ideal growth condition was got finally. The properties of GaN were characterized by X-ray diffraction and PL spectrum. The best FWHM of x-ray rocking curve is 244arcsec and the typical value is about 300arcsec. Combined with AFM result, the dislocation density in GaN was estimated to be 3 .9x 1 09cm2. The intensity of near-band-edge transition is much stronger compared with the yellowluminescence intensity, indicating perfect optical quality. The FWHM of near-band-gap transition is 22meV. Using HVPE thick GaN as template, GaN was regrown by MBE. Both the structural and optical properties can be further improved through this method. 3. The behavior of Si in GaN was investigated systematically. Varying the Si source temperature, we got n-type GaN with carrier concentration covering the range from lx 101 7cm3 to 1 xl 020cm3. Si doping can strengthen the intensity and broaden the FWHM of near-band-gap transition, however, it has little influence on YL. The broadening is modeled by taking into account potential fluctuations caused by the random distribution of donor impurities. Meanwhile, Si induced GaN bandgap renormalization has been found. We also offer experimental results to support the theoretical predication that Si can act as acceptor in GaN. Based on all experimental data, a model was proposed to illustrate the Si behavior in GaN. 4. p-type GaN was attempted using Mg and Be as dopant. 5. A1GaN/GaN heterostructure polariztion effect and modulation effect were investigated theoretically: The elastic strain and critical thickness of A1GaN on GaN were calculated. Taking the strain relax in A1GaN into consideration, the dependence of spontaneous and piezoelectric polarization induced 2DEG sheet density and sheet resistivity on A1GaN/GaN structural parameters was provided. Unlike the most conventionally used method, in which the Schrodinger and Poisson equations are solved self-consistently, we calculate the relationship between modulation doping induced 2DEG properties and AIGaN/GaN structural parameters by analysing the total energy balance in the AIGaN/GaN interface. 6. Based on the theoritical result, we design the AIGaN/GaN HFET structure, grow the HFET structure material and begin the investigation on device process: A1GaN/GaN HFET structural material was grown. X-ray results show that the material has good crystal quality. Ion etch method was employed to investigate the etch of GaN. Etch rate of 350?00 A/mm was achieved. Using Ti/Al and Pt as ohmic and schotty contact respectively, rectifying behavior has been obser...