Effect of NH3 flow on incorporation efficiency of Al composition and reduction of surface donor states in AlGaN grown by MOVPE

We have studied the effect of various ammonia (NH3) flow rates on AlGaN film grown on GaN using c-plane sapphire as substrate by metal organic chemical vapour deposition. The influences of NH3 flow on the species diffusion anisotropy of thick AlGaN films were investigated by scanning electron microscopy, atomic force microscopy and high-resolution X-ray diffraction measurements. It is demonstrated that, in addition to the larger NH3 flow, growth of the AlGaN epilayer under the same trimethylaluminum (TMAl) flow condition as others is a critical factor for less micro-cracks. The results of X-ray double crystal diffraction showed that the AlGaN films with larger ammonia flow exhibited lower Al content and smaller (0002) rocking curve width, and while NH3 flow rate reached 23 liter per minute, a (0002) rocking curve width of 295 arcsecond was reached. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)