Optical and electrical properties of MBE grown cubic GaN/GaAs epilayers doped by Si

Si-doping of cubic GaN epilayers grown by an rf plasma-assisted molecular b eam epitaxy on semi-insulating GaAs (001) substrates is investigated by sec ondary ion mass spectroscopy (SIMS), photoluminescence (PL) and by Hall-eff ect measurements. SIMS measurements show a homogeneous incorporation of Si in cubic GaN epilayers up to concentrations of 5*10(19) cm(-3). PL shows a clear shift of the donor-acceptor emission to higher energies with increasi ng Si-doping. Above a Si-flux of 1*10(11) cm(-2) s(-1) the near band edge l ines merge to one broad band due to band gap renormalization and conduction band filling effects. The influence of the high dislocation density (appro ximate to 10(11) cm(-2)) in c-GaN:Si on the electrical properties is reflec ted in the dependence of the electron mobility on the free carrier concentr ation. We find that dislocations in cubic GaN act as acceptors and are elec trically active.