Influence of growth temperature and thickness of AlGaN caps on electron transport in AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

The influence of Al0.05Ga0.95N cap thickness and growth temperature on the electrical properties of the Al0.05Ga0.95/GaN two-dimensional electron gas (2DEG) was investigated. Varying the thickness of the Al0.05Ga0.95N barrier led to regions in which the dominant 2DEG scattering mechanisms were eithe r Coulombic or interface roughness/alloy disorder scattering. The 2DEG shee t carrier concentration was found to increase with Al0.05Ga0.95N cap thickn ess and saturated at similar to 25 nm. By increasing the growth temperature from 650 degreesC to 750 degreesC. the measured low temperature 2DEG sheet carrier concentration was found to decrease and the measured low temperatu re mobility was found to increase while the Al composition remained constan t. Temperature dependent Hall measurements revealed that by increasing the growth temperature, the incorporation of impurities is decreased. A maximum 77 K mobility of similar to 19,000 cm(2)/Vs was observed for films grown a t 750 degreesC with 20 nm thick Al0.05Ga0.95N caps.