On the temperature dependent profile of interface states and series resistance characteristics in (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures

The bias dependent series resistance (Rs) and density distribution profile of interface states (Nss) of (Ni/Au)/Al0.22Ga0.78N/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 Rs of heterostructure and Rs 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 Rs. Also, the value of Rs increases with increasing temperature. The density distribution profile of Nss was obtained from high–low frequency capacitance method. In addition, the temperature dependent ac conductivity (σac) data obtained between 275 and 400 K show a linear behavior and was fitted to the Arrhenius plot. The Ea 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.