Thermodynamics of Ga<sub>2</sub>O<sub>3</sub> Heteroepitaxy and Material Growth Via Metal Organic Chemical Vapor Deposition
Indraneel Sanyal, Arpit Nandi, D. Cherns, Martin Kuball
Abstract
High Resolution Image Download MS PowerPoint Slide Heteroepitaxy of gallium oxide (Ga 2 O 3 ) is gaining popularity to address the absence of p-type doping, limited thermal conductivity of Ga 2 O 3 epilayers, and toward realizing high-quality p-n heterojunction. During the growth of β-Ga 2 O 3 on 4H-SiC (0001) substrates using metal–organic chemical vapor deposition, we observed formation of incomplete, misoriented particles when the layer was grown at a temperature between 650 °C and 750 °C. We propose a thermodynamic model for Ga 2 O 3 heteroepitaxy on foreign substrates which shows that the energy cost of growing β-Ga 2 O 3 on 4H-SiC is slightly lower as compared to sapphire substrates, suggesting similar high-temperature growth as sapphire, typically in the range of 850 °C–950 °C, that can be used for the growth of β-Ga 2 O 3 on SiC. A two-step modified growth method was developed where the nucleation layer was grown at 750 °C followed by a buffer layer grown at various temperatures from 920 °C to 950 °C. 2θ–ω scan of X-ray diffraction (XRD) and transmission electron microscope images confirm the β-polymorph of Ga 2 O 3 with dominant peaks in the (−201) direction. The buffer layer grown at 950 °C using a “ramp-growth” technique exhibits root-mean-square surface roughness of 3 nm and full width of half maxima of XRD rocking curve as low as 0.79°, comparable to the most mature β-Ga 2 O 3 heteroepitaxy on sapphire, as predicted by the thermodynamic model. Finally, the interface energy of an average Ga 2 O 3 island grown on 4H-SiC is calculated to be 0.2 J/m 2 from the cross-section scanning transmission electron microscope image, following the Wulff-Kaishew theorem of the equilibrium island shape.