Epitaxial Growth and Semiconductor Properties of NiGa ₂ O ₄ Spinel and its Interfaces with Ga ₂ O

ABSTRACT

Unintentionally formed interfacial layers are ubiquitous in semiconductor devices that operate at extreme conditions, but their structure and properties remain unknown due to the layer thinness. Here, we present epitaxial growth and semiconductor properties of NiGa ₂ O ₄ spinel and its interfaces with Ga ₂ O ₃ in high‐power and high‐temperature electronic devices. Cubic spinel NiGa ₂ O ₄ films of 2–200 nm thicknesses and low surface roughness (∼2 nm) were grown on (0001) α ‐Al ₂ O ₃ using pulsed laser deposition at substrate temperatures in the 300–900°C range. The NiGa ₂ O ₄ optical absorption onset (3.6–3.9 eV) and thermal conductivity (4–9 W m ⁻¹ K ⁻¹ ) vary systematically with substrate temperature, consistent with theoretical predictions of varying Ni and Ga cation ordering on the spinel lattice. The valence band offset at the epitaxial NiGa ₂ O ₄ /Ga ₂ O ₃ interfaces of (100) orientation is determined to be 1.8 eV using a new method that addresses limitations of traditional Kraut analysis. The NiGa ₂ O ₄ /Ga ₂ O ₃ heterojunction devices with (001) HVPE drift layers exhibit a rectification ratio of 10 ⁸ (for ± 2V) and a turn‐on voltage of 1.4 V, maintaining diode behavior up to 600°C. These results highlight the potential of NiGa ₂ O ₄ as a heterojunction partner in β ‐Ga ₂ O ₃ ‐based devices and show a new approach to investigate such interfacial layers.