The effects of LT AlN buffer thickness on the properties of high Al composition AlGaN epilayers

To fabricate nitride-based ultraviolet optoelectronic devices, a deposition process for high-Al-composition AlGaN (Al content>50%) films with reduced dislocation densities must be developed. This paper describes the growth of high-Al-composition AlGaN film on (0001) sapphire via a LT AlN nucleation layer by low pressure metalorganic chemical vapor deposition (LPMOCVD). The influence of the low temperature AlN buffer layer thickness on the high-Al-content AlGaN epilayer is investigated by triple-axis X-ray diffraction (TAXRD), scanning electron microscopy (SEM), and optical transmittance. The results show that the buffer thickness is a key parameter that affects the quality of the AlGaN epilayer. An appropriate thickness results in the best structural properties and surface morphology.