Al composition dependent properties of quaternary AlInGaN Schottky diodes

Pd Schottky barrier diodes were fabricated on undoped AlxIn0.02Ga0.98−xN∕GaN with x less than 20%. The material properties, which were characterized by photoluminescence, x-ray diffraction, and atomic force microscopy, indicated that the quaternary samples were coherently grown on GaN template with high crystalline quality. The flatband barrier height obtained by capacitance-voltage (C-V) measurement increased with increasing Al mole fraction (increasing the band gap of the quaternary) up to 2.06eV, in agreement with the predictions of the Schottky-Mott theory. However, current-voltage (I-V) measurements revealed that the barrier height decreased from 1.32to1.12eV, which was accompanied by an increase in ideality factor from 1.04 to 1.73. The large difference of barrier height between I-V and C-V measurements could not be quantitatively explained by the traditional electron transport mechanisms of Schottky diode, such as tunneling effect, image force effect, and barrier inhomogeneity theory. Strong polari...