Electrical Properties of Vertical p‐NiO/n‐Ga₂O₃ and p‐ZnCo₂O₄/n‐Ga₂O₃ pn‐Heterodiodes

Abstract

Vertical β ‐Ga 2 O 3 ‐based pn‐heterostructures are investigated by current–voltage measurements and thermal admittance spectroscopy. The β ‐Ga 2 O 3 thin films are grown by pulsed laser deposition (PLD) on (00.1)ZnO:Ga/(11.0)Al 2 O 3 substrates at 670 °C. Two different p‐type oxides are used to fabricate pn‐heterodiodes which are investigated with respect to rectification, temperature stability, and breakdown behavior. For that, p‐NiO and p‐ZnCo 2 O 4 are grown by PLD at room temperature on top of a β ‐Ga 2 O 3 thin film, respectively. The rectification ratio at room temperature is about nine orders of magnitude, the ideality factor is about 2 and the on‐resistance is below 1 Ω cm 2 . Both diode types did not show degradation for temperatures up to 100 °C. Thermal admittance spectroscopy revealed defects in β ‐Ga 2 O 3 with thermal activation energy E a of about 200 meV for both diode types. Additionally, a level with E a ≈ 240 meV is detected for the NiO/Ga 2 O 3 diodes only. In general, both diode types are suited to realize pn‐heterodiodes with high rectification, but NiO is especially interesting for defect characterization by deep‐level optical spectroscopy due to its transparency up to about 3.7 eV.