Growth and defect characterization of doped and undoped beta-Ga2O3 crystals

Much excitement has surrounded the accelerating development of beta-Ga2O3 for electronics due to its ultrawide band gap, high breakdown voltage, compatibility with many dopants, and comparative ease of producing large substrates via melt-growth techniques. Our research has focused on growth and characterization of Czochralski (CZ) and vertical gradient freeze (VGF) single crystals of beta-Ga2O3 with various dopants, including donors (Zr, Hf, Cr), acceptors (Mg, Zn, Fe, Ni, Cu), and alloying elements (Al). We find in general that doping in CZ and VGF materials can be different and sometimes non-uniform due to the interaction with crucible material (Ir), selective evaporation, and thermal profile. We have also explored the creation and identification of gallium vacancies (V-Ga) through annealing, by using positron annihilation spectroscopy (PAS), hydrogenated Fourier Transform Infrared (FTIR) spectroscopy, and electrical measurements. Different analysis techniques probe different spatial and depth averages, and thus careful consideration must be given to correctly interpret results and significance of defect concentrations determined. Insights from our work to date are offered, in terms of their applicability to devices.