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High work-function metals such as Ni, Pt, and Au in the form of multilayer structures, Ni/Au and Ni/Pt/Au, have been investigated as Schottky metallizations on AlGaN/GaN heterostructures under thermal annealing. As-deposited Ni/Pt/Au had slightly higher Schottky barrier height than its Ni/Au counterpart. Schottky barrier heights for Ni/Au diodes on AlGaN/GaN increased by about 20% from 1.02 eV for as-deposited to 1.21 eV after annealing at 500 °C for 2 min. Similar trends were observed for Ni/Pt/Au Schottky diodes. Thermal stability study for these devices showed that the interposition of Pt in Ni/Au systems improved the characteristics of the Schottky diodes after short-term anneal but cause significant degradation after long-term anneal at 500 °C. Ni/Au Schottky contacts exhibited excellent leakage response under thermal annealing for long periods. Microstructural studies were carried out on Ni/Pt/Au and Ni/Au Schottky contacts to elucidate the role of the Pt interlayer in the degradation of the Ni/Pt/Au metallization under long-term thermal anneal.
Ofuonye et al. (2014) studied this question.