γ -phase inclusions as common structural defects in alloyed β -(Al x Ga 1−x ) 2 O 3 and doped β -Ga 2 O 3 films

Chang, Celesta S.; Tanen, Nicholas; Protasenko, Vladimir; Asel, Thaddeus J.; Mou, Shin; Xing, Huili Grace; Jena, Debdeep; Muller, David A.

doi:10.1063/5.0038861

Ultrawide bandgap β-(Al x Ga 1 −x ) 2 O 3 vertical Schottky barrier diodes on (010) β-Ga 2 O 3 substrates are demonstrated. The β-(Al x Ga 1 −x ) 2 O 3 epilayer has an Al composition of 21% and a nominal Si doping of 2 × 10 17 cm −3 grown by molecular beam epitaxy. Pt/Ti/Au has been employed as the top Schottky contact, whereas Ti/Au has been utilized as the bottom Ohmic contact. The fabricated devices show excellent rectification with a high on/off ratio of ∼10 9 , a turn-on voltage of 1.5 V, and an on-resistance of 3.4 mΩ cm 2 . Temperature-dependent forward current-voltage characteristics show effective Schottky barrier height varied from 0.91 to 1.18 eV while the ideality factor from 1.8 to 1.1 with increasing temperatures, which is ascribed to the inhomogeneity of the metal/semiconductor interface. The Schottky barrier height was considered a Gaussian distribution of potential, where the extracted mean barrier height and a standard deviation at zero bias were 1.81 and 0.18 eV, respectively. A comprehensive analysis of the device leakage was performed to identify possible leakage mechanisms by studying temperature-dependent reverse current-voltage characteristics. At reverse bias, due to the large Schottky barrier height, the contributions from thermionic emission and thermionic field emission are negligible. By fitting reverse leakage currents at different temperatures, it was identified that Poole–Frenkel emission and trap-assisted tunneling are the main leakage mechanisms at high- and low-temperature regimes, respectively. Electrons can tunnel through the Schottky barrier assisted by traps at low temperatures, while they can escape these traps at high temperatures and be transported under high electric fields. This work can serve as an important reference for the future development of ultrawide bandgap β-(Al x Ga 1 −x ) 2 O 3 power electronics, RF electronics, and ultraviolet photonics.

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