Investigation of the electronic properties of nitrogen vacancies in AlGaN

The effects of premetallization annealing on the electrical characteristics of GaN and AlxGa1-xN (x=0.25 and 0.5) Schottky diodes have been studied. Annealing above 800 degrees C in an Ar ambient led to a significant preferential N loss, and annealing at 1000 degrees C caused localized surface decomposition. The Pt/Au Schottky contacts on the annealed GaN became leakier, whereas those on the thermally damaged AlGaN exhibited more rectifying characteristics. Prolonged annealing produced more conductive AlGaN surfaces deficient in both N and Al, as revealed by x-ray photoelectron spectroscopy. These findings suggest that, as opposed to donorlike vacancies in GaN, N vacancies in AlGaN with an Al mole fraction >= 25% behave as deep-level states, compensating the near-surface region. Care must therefore be taken to prevent the loss of N during thermal processing of high-Al content AlGaN.