n- and p-type doping of cubic GaN

N-type doping with Si and p-type doping with Mg and C of cubic GaN (c-GaN) epilayers are reported. The cubic GaN films were grown by rf-plasma assisted molecular beam epitaxy (MBE) on semi-insulating GaAs (001) substrates at a substrate temperature of 720degreesC. Elemental Mg and Si were evaporated from thermal effusions cells whereas C-doping of c-GaN was achieved by e-beam. evaporation off a graphite rod. Secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (PL) and temperature dependent Hall-effect measurements were used to study the incorporation and the optical and electrical properties. Si-doped c-GaN epilayers were n-type with electron concentrations up to 5x10(19) cm(-3) and the incorporation of Si followed exactly the vapor pressure curve of Si. Successful p-type doping was achieved with both Mg and C at room temperature with maximum hole concentrations of about 2x10(16)cm(-3) and 6x10(17)cm(-3), respectively. In both cases, however, at high dopant concentrations deep compensating defects limited the maximum free hole concentration. From optical measurements the acceptor binding energies of C (215 meV) was found to be less than for Mg (230 meV). Therefore, in cubic GaN p-type doping with C seems to be more suitable than with Mg.