Electrically active oxide defects in Ni/Al2O3/4H-SiC diodes mimicking CAV-related defect levels

Accurate identification of electrically active defects is essential for understanding and controlling the electronic and optical properties of semiconductors. In this work, we investigate electrically active defect levels in Ni/Al2O3/4H-SiC vertical Schottky diodes, where Al2O3 passivation is employed to suppress surface-related defects. The devices exhibit highly uniform Schottky behavior over a 0.07 cm2 contact area, extremely low reverse-bias leakage governed by Poole–Frenkel–type defect-assisted transport, and a low interface trap density on the order of 109 cm−2eV−1. Capacitance-mode deep-level transient spectroscopy reveals the presence of Z1/2 centers as well as a broad high-energy feature. While the Z1/2 center is readily identified, the high-energy feature cannot be adequately deconvoluted using physics-based fitting alone and is subsequently resolved by isothermal transient spectroscopy into two distinct defect levels at EC− 1.05 eV and EC− 1.1 eV. These levels are identified as oxidation-induced ON2a and ON2b defects, which closely overlap in energy with the carbon-antisite–carbon-vacancy pair related EH4 and EH5 defects that are of interest for qubit applications. In contrast, defects such as ON2a/b have been reported as electrically active oxide-related states that are regarded as non-qubit or “dark” defect states. These results highlight the importance of careful defect identification when interpreting electrical spectroscopy in oxidized SiC structures, particularly in studies where electrically detected defect levels are used to infer the presence of candidate quantum defects.