Rapid-thermal-annealing-induced microstructural evolution of Au/Ni/β-Ga₂O₃ Schottky diodes correlated with their electrical properties

This study investigated the rapid thermal annealing (RTA)-induced phase and microstructural evolution of Au/Ni/β-Ga₂O₃ Schottky diodes to demonstrate their effect on the diodes’ electrical properties in the temperature range of 400–700 °C. Annealing at 500 °C led to a reaction between the Au and Ni films, forming Au-rich Au₃Ni and Ni-rich AuNi₃ phases along with a homogeneous AuNi alloy phase with a smooth surface and interface morphology. Only the Au₂Ni phase formed after RTA at temperatures above 600 °C. Reactions did not occur between the Ni/Au metal contacts and the Ga₂O₃ substrate, regardless of the RTA temperature. The Au/Ni/β-Ga₂O₃ Schottky diode annealed at 500 °C exhibited improved rectifying behavior with a large barrier height (1.22 eV) and large breakdown voltage (V_br) of 460 V, which may be associated with the formation of Au-Ni alloy films with a smooth surface morphology and abrupt interface with the Ga₂O₃ substrate. The Schottky diode behavior began to degrade upon RTA at 600 °C, which is attributed to the initiation of degradation of the surface and interface morphology of the Au₂Ni alloy film. The deterioration of the Schottky behavior with the drastic increase of the reverse leakage current and sharp drop of V_br upon RTA at 700 °C is attributed to the severe deterioration of the interface and surface morphologies, such as the roughened surfaces caused by agglomeration and void formation with the grain boundaries serving as high leakage current paths.