Low Al-content n-type Al_xGa_1−xN layers with a high-electron-mobility grown by hot-wall metalorganic chemical vapor deposition

In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n-Al_xGa_1−xN (x = 0 – 0.12, [Si] = 1×10¹⁷ cm⁻³) epitaxial layers on 4H-SiC(0001). All layers are crack-free, with a very small root mean square roughness (0.13 – 0.25 nm), homogeneous distribution of Al over film thickness and a very low unintentional incorporation of oxygen at the detection limit of 5×10¹⁵ cm⁻³ and carbon of 2×10¹⁶ cm⁻³. Edge type dislocations in the layers gradually increase with increasing Al content while screw dislocations only raise for x above 0.077. The room temperature electron mobility of the n-Al_xGa_1−xN remain in the range of 400 – 470 cm²/(V.s) for Al contents between 0.05 and 0.077 resulting in comparable or higher Baliga figure of merit with respect to GaN, and hence demonstrating their suitability for implementation as drift layers in power device applications. Further increase in Al content is found to result in significant deterioration of the electrical properties.