The role of growth conditions on the p-doping of GaN by plasma-assisted molecular beam epitaxy

Mg-doped GaN layers were grown by plasma-assisted molecular beam epitaxy under a range of conditions. The growth temperatures and III/V ratio were altered and the resultant films were analyzed using atomic force microscopy, Hall effect measurements, and secondary ion mass spectroscopy (SIMS). The growth temperatures ranged from 600degreesC to 700degreesC. The III/V ratios were varied from N-rich (less than unity) to Ga-rich conditions (greater than unity). AFM showed that N-rich (III/V ratio<1) conditions yielded rough surface morphologies and room temperature Hall measurements show they were not measurably p-type. Ga-rich conditions (III/V ratio>1) yielded smoother morphologies and exhibited p-type conductivity. The trend in morphology with changing III/V ratio is consistent with previous studies of the MBE growth of unintentionally doped GaN. SIMS measurements show that Mg incorporation was negligibly affected by the III/V ratio but exponentially decreased with increasing growth temperature. (C) 2002 Published by Elsevier Science B.V.