Effect of Mg Doping on the Photoluminescence of GaN:Mg Films by Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy

We investigate undoped GaN and Mg-doped GaN grown by rf plasma-assisted molecular beam epitaxy(MBE)with different Mg concentrations by photoluminescence(PL)at low temperature,Hall-effect and XRD measurements.In the PL spectra of lightly Mg-doped GaN films,a low intensity near band edge(NBE)emission and strong donor-acceptor pair(DAP)emission with its phonon replicas are observed.As the Mg concentration is increased,the DAP and NBE bands become weaker and a red shift of these bands is observed in the PL spectra.Yellow luminescence(YL)is observed in heavily Mg-doped GaN.The x-ray diffraction is employed to study the structure of the films.Hall measurement shows that there is a maximum value(3.9×10^(18) cm^(−3))of hole concentration with increasing Mg source temperature for compensation effect.PL spectra of undoped GaN are also studied under N-rich and Ga-rich growth conditions.Yellow luminescences of undoped Ga-rich GaN and heavily Mg-doped GaN are compared,indicating the different origins of the YL bands.