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

K. Tetzner¹, Z. Galazka², A. Thies¹, A. Külberg¹, and O. Hilt¹

Published in:

Appl Phys Lett, vol. 128, pp. 243307, doi:10.1063/5.0336434 (2026).

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 2.1x10¹⁷cm^-3 as well as a built-in potential of 1.7V. The devices exhibit excellent rectification with an on/off current ratio exceeding 10¹⁰ at 63V, a turn- on voltage of ~1V, and a high forward current density of 376A/cm² at 3V. A low differential specific on-resistance of 4.4 mΩcm² demonstrates efficient carrier transport and effective backside Ohmic contact formation. Furthermore, an apparent Schottky barrier height of 1.17eV 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 132V is achieved, corresponding to an estimated electric field of 2.8MV/cm. These results highlight the potential of r-GeO₂ as a promising ultra-wide bandgap semiconductor for next-generation power electronic devices and applications.

© 2026 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)
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