Effect of AlN/GaN supercycle ratio on properties of AlxGa1_xN films using super-cycle plasma enhanced atomic layer deposition

In this study, aluminum gallium nitride (AlGaN) films are prepared by supercycle plasma enhanced vapor deposition (PEALD) with trimethylgallium, trimethylaluminum, and NH3 plasma. The ratio of aluminum nitride (AlN) to gallium nitride (GaN) PEALD cycle number is varied to investigated its effect on film properties. The experimental results show that the growth per cycle is lower than that of the mixing rule prediction, and the Ga content dramatically drops with increasing the AlN cycle ratio. It is implied that AlN surface partly hinders the growth of GaN during supercycle deposition. The Ga:Al elemental ratio is found to be 1:1 at the AlN cycle ratio of 20%, beyond which the film transforms from Ga-rich to Ga-poor and is accompanied with increased Al -Al metallic bonds. The film with the 20% AlN cycle ratio also exhibits the least aggregated surface morphology. The elemental depth profile investigated using secondary ion mass spectroscopy indicates an uniform distribution of Ga, Al and N. The bandgap of supercycle PEALD AlGaN films can be tuned when the AlN cycle ratio is less than 20%. Moreover, the AlGaN film with 20% AlN cycle ratio shows a photoluminescence peak centered at 277 nm, agreeing with the bandgap of the film.