Influence of magnesium doping on the structural properties of GaN layers

We investigate the incorporation of magnesium in gallium nitride (GaN) films deposited on (0001) sapphire (c-Al2O3) substrates by low-pressure metalorganic chemical vapor-phase deposition (MOCVD). The growth, structure and optical properties of GaN samples with a dopant concentration ranging from 10(17) to 10(21) cm(-3) have been studied using transmission electron microscopy and micro-Raman spectroscopy. The growth rate and sample quality are strongly influenced by the amount of magnesium incorporated in the sample, with the inclusion of cubic GaN on the otherwise hexagonal material and a disruption of the two-dimensional growth for the highest dopant concentrations. The presence of the cubic phase is accompanied by the formation of large triangular islands due to a local increase of growth rate for a dopant concentration exceeding 10(20) cm(-3).