Gallium-oxide trench-type devices

Gallium oxide (β-Ga₂O₃) is a suitable material for next generation high power devices because of its huge critical electric field strength. However, most current device structures are not enough to take advantage of the full potential of Ga₂O₃ because these structures are optimized for material properties of silicon. To bring out the potential of Ga₂O₃, we propose a trench structure. First, we made Ga₂O₃ metal-oxide-semiconductor Schottky barrier diodes (MOSSBDs). The HfO₂ film was deposited on the trench bottom and sidewall. Ga₂O₃ MOSSBD had a small leakage current level, and had about a 40% lower forward voltage than that of the commercially available SiC SBDs. We thus successfully demonstrated that the performance of Ga₂O₃ devices can exceed that of SiC devices. Next, we made Ga₂O₃ junction barrier Schottky (JBS) diodes. p-type region was made by p-type NiO. The Ga₂O₃ JBS diode had several orders of magnitude smaller leakage current than that of the normal SBD. This result indicates that the electric field at the Schottky junction decreased as a result of using the JBS structure. Finally, we fabricated Ga₂O₃ trench MOS field effect transistors. We used a static induction transistor-type structure that can be made only with n-type semiconductors. Si-doped Ga₂O₃ n⁺ contact and n^-drift layers were grown on Sn-doped (001) Ga₂O₃ substrate with HVPE. The gate dielectric was HfO₂. The device showed clear current modulation characteristics and a maximum current density of 1.36 kA/cm². The device had a high on-off ratio of over 10⁷.