Monoclinic β-Ga₂O₃ has attracted significant attention as a high power electronics material based on its ultra-wide energy gap (4.9 eV), high theoretical critical field (8 MV/cm), as well as the commercially availability of inexpensive substrates grown from the melt. In order to achieve breakdown field consistent with the theoretical expectations, however, very high quality epitaxial films with very low doping and defect density will be required. Wong et al. have reported a β-Ga₂O₃ MOSFET with carrier concentration below 4x10¹⁴ cm^-3, which is the lowest reported value for epitaxial β-Ga₂O₃ to date [1]. This talk will discuss the structural and electronic properties for thick homoepitaxial β-Ga₂O₃ with doping as low as 8x10¹² cm^-3, corresponding to breakdown voltage in excess of 2.38 kV (3.18 MV/cm), measured without field termination for vertical measurements or edge effects correction in the case of lateral devices. Our results show that current β-Ga₂O₃ halide vapor phase epitaxial technology can produce epilayers with breakdown field approaching the theoretical value of GaN. In addition, we will discuss the annealing of bulk and epitaxial β-Ga₂O₃ films in O₂ atmosphere as a potential pathway to reduce carrier concentration and possibly improve the breakdown voltage of Ga₂O₃ Schottky diodes. We show that annealing Ga₂O₃ in O₂ will reduce N_D-N_A by about an order of magnitude, similar to earlier observations by Kuramata et al. [2]. Furthermore, we will present our approach for overcoming the polaron-induced suppression of room-temperature p-type conductivity in Ga₂O₃, causing holes to preferentially self-trap instead of being available as free carriers [3]. We show that natural p-type semiconducting oxides such as NiO can be integrated with β-Ga₂O₃ to form a rectifying heterojunction as a fundamental building block for any viable Ga₂O₃ power device. Finally, we will discuss the low thermal conductivity of Ga₂O₃ and present our preliminary thermal management simulations and experimental results.

[1] A. Kuramata, et al., Jpn. Jour. Appl. Phys. 55, 1202A2 (2016).

[2] M.H. Wong, et al., Appl. Phys. Express 10, 041101 (2017).

[3] J.B. Varley, et al., Phys. Rev. B 85, 081109(R) (2012).