Growth of ultrathin barrier InAlGaN/GaN heterostructures with superior properties using sputtered AlN/sapphire templates and optimized group-III injection rate by metalorganic chemical vapor phase deposition

•High-quality thin GaN can be grown on sputtered AlN/sapphire templates.•TrimethylIndium promotes Ga into InAlGaN resulting in smoother surface and higher mobility.•Higher Trimethylaluminim deteriorated surface leading to the degraded electrical properties.•High mobility with high crystallinity of ultrathin InAlGaN barrier is achieved.