Effect of the trimethylgallium flow during nucleation layer growth on the properties of GaN grown on sapphire

We report on the effect of the trimethylgallium Bow during nucleation layer growth on the electrical; optical and structural properties of epitaxial GaN films grown on basal plane sapphire by atmospheric pressure metalorganic chemical vapor deposition. The 1.2 mu m thick GaN films grown on nucleation layers with the optimum trimethylgallium flow of 45 mu mol/min had a room temperature mobility of 644 cm(2)/s and minimum width of the (002) and the (102) X-ray diffraction peaks. The roughness of the as-grown nucleation layers decreased with increased trimethylgallium Bow. However, smooth, as-grown, nucleation layers showed a strong tendency for island coarsening and an increased surface roughness after heating to the bulk GaN growth temperature.