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 (ϕb0) and the series resistance (Rs) increase with increasing temperature. Such temperature dependence of ϕb0 and Rs is in obvious disagreement with the reported negative temperature coefficient. An apparent increase in the ideality factor (n) and a decrease in the ϕb0 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 () of 1.108 eV and 0.649 eV, and standard deviations (σs) of 0.137 V and 0.077 V, respectively. Furthermore, the temperature dependence of the energy distribution of interface state density (Nss) profiles has been determined from forward bias I–V measurements by taking into account the bias dependence of the effective barrier height (ϕe) and n. The fact that the values of Nss increase with increasing temperature has been attributed to the molecular restructuring and reordering at the metal/semiconductor interface under the effect of temperature.