Gallium-oxide trench-type devices

Abstract

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.