P- and N-type doping of non-polar A-plane GaN grown by molecular-beam epitaxy on R-plane sapphire

Non-polar a-plane GaN films doped with Si or Mg were grown by plasma-assisted molecular-beam epitaxy on r-plane sapphire substrates. The (11 (2) over bar0) orientation of the GaN epilayers was confirmed by x-ray diffraction. The layers were further characterized by atomic force microscopy, Hall effect, and photoluminescence measurements. The Mg-doped layers showed p-type conductivity, with a maximum hole concentration of 6 x 10(17) cm(-3) (mu = 2 cm(2)/Vs). Comparison with Mg-doping of N-polar c-plane GaN suggests the Mg sticking coefficient may be higher on the GaN (11 (2) over bar0) surface compared to the GaN ( 0001) surface. The electron mobility obtained for a-plane GaN: Si (18 cm(2)/ Vs for n = 1 x 10(18) cm(-3)) was low compared to that of typical c-plane epilayers. The lower electron mobility is attributed to the higher density of structural defects in a-plane GaN.