Vertical r-GeO2 Schottky barrier diodes on single-crystal r-GeO2 substrates

Abstract

In this work, we report on the electrical characterization of vertical r-GeO2 Schottky barrier diodes (SBDs) fabricated on low-doped single-crystal r-GeO2 substrates using Ni-based Schottky contacts. Capacitance–voltage analysis reveals a donor concentration of 2.1 × 1017 cm−3 as well as a built-in potential of 1.7 V. The devices exhibit excellent rectification with an on/off current ratio exceeding 1010 at ±3 V, a turn-on voltage of ∼1 V, and a high forward current density of 376 A/cm2 at 3 V. A low differential specific on-resistance of 4.4 mΩ cm2 demonstrates efficient carrier transport and effective backside Ohmic contact formation. Furthermore, an apparent Schottky barrier height of 1.17 eV and an ideality factor of 1.21 are extracted. Temperature-dependent J–V measurements from 25 to 200 °C reveal thermally activated forward conduction transitioning toward thermionic-field emission at elevated temperatures, consistent with barrier inhomogeneity. Moreover, reverse leakage currents remain nearly temperature-independent, emphasizing the high thermal stability of the SBDs. Finally, a median breakdown voltage of 132 V is achieved, corresponding to an estimated electric field of 2.8 MV/cm. These results highlight the potential of r-GeO2 as a promising ultra-wide bandgap semiconductor for next-generation power electronic devices and applications.