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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 ND-NA 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). |
