The influence of series resistance and interface states on intersecting behavior of I-V characteristics of Al/TiO2/p-Si (MIS) structures at low temperatures

Abstract

In this study, we have investigated the intersection behavior of the forward bias current-voltage (I-V) characteristics of the Al/TiO2/p-Si (MIS) structures in the temperature range of 100 300 K. The intersection behavior of the I-V curves appears as an abnormality when compared to the conventional behavior of ideal Schottky diodes and MIS structures. This behavior is attributed to the lack of free charge at a low temperature and in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures, in particular. The values calculated from the temperature-dependent forward bias I-V data exhibit unusual behavior, where the zero-bias barrier height (phi(b0)) and the series resistance (R-s) increase with increasing temperature. Such temperature dependence of phi(b0) and R-s is in obvious disagreement with the reported negative temperature coefficient. An apparent increase in the ideality factor (n) and a decrease in the phi(b0) at low temperatures can be attributed to the inhomogeneities of the barrier height, the thickness of the insulator layer and non-uniformity of the interfacial charges. The temperature dependence of the experimental I-V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double Gaussian distribution with mean barrier height values ((phi) over bar (b0)) of 1.108 eV and 0.649 eV, and standard deviations (sigma(s)) of 0.137 V and 0.077 V, respectively. Furthermore, the temperature dependence of the energy distribution of interface state density (N-ss) profiles has been determined from forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (phi(e)) and n. The fact that the values of N-ss increase with increasing temperature has been attributed to the molecular restructuring and reordering at the metal/semiconductor interface under the effect of temperature.