Thermal stability of Schottky contacts on strained AlGaN/GaN heterostructures

Abstract

The thermal stability of Ni Schottky contacts on strained Al0.3Ga0.7N/GaN heterostructures and on n-type bulk GaN was investigated after various thermal stressings using capacitance–voltage and current–voltage characterization techniques. The reverse leakage current decreases after thermal treatment at up to 800 and 600 °C for Schottky contacts on the strained Al0.3Ga0.7N/GaN heterostructures and bulk n-GaN, respectively. Ni Schottky contacts on the heterostructure with 30-min thermal stressing at 700 °C exhibit lower reverse leakage current by more than three orders of magnitude lower than the control sample. However, decrease in two-dimensional electron gas sheet carrier concentration at the Al0.3Ga0.7N and GaN interface possibly due to interactions between Ni and AlGaN surface was observed with increase of stressing temperature and time. Ni Schottky contacts on bulk n-GaN layers degrade at lower annealing temperature and their rectifying property practically disappears after 700 °C annealing, while Al0.3Ga0.7N/GaN heterostructures still exhibit nice Schottky behavior after 800 °C annealing. The better thermal stability of Ni Schottky contacts on the heterostructures than those on bulk n-GaN can be attributed to the presence of piezoelectric polarization.