On the temperature dependent profile of interface states and series resistance characteristics in (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructures

Abstract

The bias dependent series resistance ( R s ) and density distribution profile of interface states ( N ss ) of (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructure have been investigated by admittance measurements in a wide temperature range of 80–400 K. Experimental results show that both the values of capacitance ( C) and conductance ( G/ ω) were found to be strongly temperature and applied bias voltage dependent. The capacitance–voltage ( C– V) plots give a peak especially at high temperatures in the depletion region and disappear at low temperatures. When the temperature was increased both the values of C and G/ ω reduced. This decrease of capacitance can be understood if the dielectric constant of interfacial layer decreases with increasing temperature. Such temperature dependent behavior of C and G/ ω also can be attributed to the thermal restructuring and reordering of the interface states. The downward curvatures in C– V plots have been attributed to the R s of heterostructure and R s may cause a large deviation in C– V and G/ ω– V data. Therefore, the entire C– V and G/ ω– V measurements were corrected for the effect of R s . Also, the value of R s increases with increasing temperature. The density distribution profile of N ss was obtained from high–low frequency capacitance method. In addition, the temperature dependent ac conductivity ( σ ac ) data obtained between 275 and 400 K show a linear behavior and was fitted to the Arrhenius plot. The E a values were obtained from the slope of ln σ vs 1/ T plots to be −58.5, −59.7, −60.4 and −60.6 meV for the applied biases of −4, −3, −2 and −1 V, respectively.