Carrier transport mechanism of AlGaN/GaN Schottky barrier diodes with various Al mole fractions



The evolution of the dominant carrier transport mechanism of Alx Ga1-xN/GaN Schottky barrier diodes with increasing Al mole fraction x (x = 0.2, 0.3, 0.4, and 0.5) is investigated. The Schottky barrier height (SBH) linearly increases with the work function of Schottky metal with the slope factor of ∼0.5 irrespective of x. The SBH, the ideality factor, and the reverse leakage current, however, show an increasing deviation from the predicted values given by the thermionic-emission theory as x increases. The XPS analysis reveals enhanced predominant incorporation of oxygen donors and an increase in the energy band bending at the surface of AlGaN with increasing x, indicating that the carrier transport by tunnelling through the thin, heavily doped Schottky barrier becomes dominant. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)