GAS-SOURCE MOLECULAR-BEAM EPITAXY OF III-V NITRIDES

Amorphous, hexagonal and cubic phases of BN were grown via ion beam as sisted deposition on Si(100) substrates. Gas-source molecular beam epi taxy of the III-V nitrides is reviewed. Sapphire(0001) is the most com monly employed substrate with 6H-SiC(0001), ZnO(111) and Si(111) also being used primarily for the growth of wurtzite GaN(0001) in tandem wi th previously deposited GaN(0001) or AlN(0001) buffer layers. Silicon( 001), GaAs(001), GaP(001) and 3C-SiC(001) have been employed for growt h of cubic (zincblende) beta-GaN(001). The precursor materials are eva porated metals and reactive N species produced either via ECR or RF pl asma decomposition of N-2 or from ammonia. However, point defect damag e from the plasma-derived species has resulted in a steady increase in the number of investigators now using ammonia. The growth temperature s for wurtzite GaN have increased from 650 +/- 50 degrees C to 800 +/- 50 degrees C to enhance the surface mobility of the reactants and, in turn, the efficiency of decomposition of ammonia and the microstructu re and the growth rate of the films. Doping has been achieved primaril y with Si (donor) and Mg (acceptor); the latter has been activated wit hout post-growth annealing. Simple heterostructures, a p-n junction LE D and a modulation-doped field-effect transistor have been achieved us ing GSMBE-grown material.