In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n-AlxGa1−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-AlxGa1−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.

Thick GaN layers with a low concentration of defects are the key to enable next-generation vertical power electronic devices. Here, we explore hot-wall metalorganic chemical vapor deposition (MOCVD) for the development of GaN homoepitaxy. We propose a new approach to grow high quality homoepitaxial GaN in N2-rich carrier gas and at a higher supersaturation as compared to heteroepitaxy. We develop a low temperature GaN as an optimum nucleation scheme based on the evolution and thermal stability of the GaN surface under different gas compositions and temperatures. Analysis in the framework of nucleation theory of homoepitaxial layers simultaneously grown on GaN templates on SiC and on hydride vapor phase epitaxy GaN substrates is presented. We show that residual strain and screw dislocation densities affect GaN nucleation and subsequent growth leading to distinctively different morphologies of GaN homoepitaxial layers grown on GaN templates and native substrates, respectively. The established comprehensive picture provides a guidance for designing strategies for growth conditions optimization in GaN homoepitaxy. GaN with atomically flat and smooth epilayer surfaces with a root-mean-square roughness value as low as 0.049 nm and low background carbon concentration of 5.3 x 1015 cm-3 has been achieved. It is also shown that there is no generation of additional dislocations during homoepitaxial growth. Thus, our results demonstrate the potential of the hot-wall MOCVD technique to deliver high-quality GaN material for vertical power devices.

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Thermal conductivity of AlxGa1-xN layers with 0 <= x <= 0.96 and variable thicknesses is systematically studied by combined thermoreflectance measurements and a modified Callaway model. We find a reduction in the thermal conductivity of AlxGa1-xN by more than one order of magnitude compared to that of GaN, which indicates a strong effect of phonon-alloy scattering. It is shown that the short-mean free path phonons are strongly scattered, which leads to a major contribution of the long-mean free path phonons to the thermal conductivity. In thin layers, the long-mean free path phonons become efficiently scattered by the boundaries, resulting in a further decrease in the thermal conductivity. Also, an asymmetry of thermal conductivity as a function of Al content is experimentally observed and attributed to the mass difference between Ga and Al host atoms.