Growth of High-Resistivity Wurtzite and Zincblende Structure Single Crystal Gan by Reactive-Ion Molecular Beam Epitaxy

ABSTRACTEpitaxial GaN films have been grown at temperatures between 600 and 900 °C by reactive-ion molecular-beam epitaxy. Ga was provided by evaporation from an effusion cell while nitrogen was supplied from a low-energy, single-grid, ion source. The average energy per accelerated N incident at the growing film surface was ≈ 19 eV. Films deposited on Al2O3(0112) and MgO(100)l×l substrates had wurtzite (a-GaN) and metastable zincblende (α-GaN) structures, respectively. The lattice constants were a = 0.3192 nm and c = 0.5196 nm for α;-GaN and a = 0.4531 nm for β -GaN. The room-temperature optical bandgap Eg of zincblende GaN, 3.30 eV, was found to be 0.11 eV lower than that of the hexagonal polymorph α-GaN. All films were n-type with electron carrier concentrations which decreased from 4×1018 to 8×1013 cm−3 with increasing incident N2+/Ga flux ratios between 0.63 and 3.9. Resistivities <106Ω-cm were achieved.