Growth And Characterization Of GaN And AIGaN By RFP-MBE

This dissertation mainly focused on the growth and characterization of GaN based materials grown by radio frequency plasma assisted molecular beam epitaxy (RFP-MBE). Some of the devices related technics, such as etching and ohmic contact, were also discussed. Based on the experimental results, the growth conditions for GaN were optimized, and several key problems were investigated. All the work includes the reconstruction of MBE system, pre-treatment of sapphire substrate, growth of the buffer layer, optimizing of epi-layer growth, the characterizing of polarity, wet etching, ohmic contact, etc. The main results achieved in this work are listed as follows:1. Based on the original system, we reconstructed the growth chamber, and uniformed the auxiliary equipments. The growth rate of 0.5|_im/h was obtained.2. The growth conditions for GaN epi-layers were established and optimized on our RFP-MBE system. It was shown that the FWHM of oo/26 rocking curve for the GaN sample is 240 arcsec. The yellow peak in PL measurement is eliminated. The rms roughness of the epi-layer surface is <5 A, and the intrinsic carrier density is ~1016cm~3, the dislocation density is ~lx!09cm"2.3. The pre-treatments technics of sapphire surface were successfully established, including chemical cleaning, high temperature annealing, nitridation, and Ga-atom polishing. The technics of Ga-atom polishing was the first time to be used and the roughness of epi-layer surface was improved obviously.4. Started with nucleation growth, we examined the function of buffer layer, and established the double-buffer layer structure. As a result, the rms roughness of GaN epi-layer was controlled in a few angmstrom.5. The characterization of polarity was established by photo-assisted wet etching and the growth conditions to get controlled polar GaN epi-layer were studied. It was found that the nucleation temperature is one of the critical factors to influence the polarity of the epi-layer. The two kinds of polar GaN films can be achieved by suing different growth conditions.6. A new method was established to evaluate the dislocation density of n-polar GaN by photo-assisted wet etching.7. By cooperating with other researchers, the Ti/Al alloy technics was established and a contact resistivity of lxlO~5Q*cm2 was obtained.