The double Gaussian distribution of barrier heights in Al/TiO2/p-Si (metal-insulator-semiconductor) structures at low temperatures

Abstract

The current-voltage (I-V) characteristics of Al/TiO2/p-Si metal-insulator-semiconductor (MIS) structures have been investigated in the temperature range of 80-300 K. An abnormal decrease in the zero bias barrier height (BH) (phi(b0)) and an increase in the ideality factor (n) with decreasing temperature have been explained on the basis of the thermionic emission (TE) theory with Gaussian distribution (GD) of the BHs due to the BH inhomogeneities. The temperature dependence of the experimental I-V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double GD with mean BH values ((phi) over bar (b0)) of 1.089 and 0.622 eV and standard deviations sigma(s) of 0.137 and 0.075 V, respectively. Thus, the modified ln(I-0/T-2)-q(2)sigma(2)(0)/2(kT)(2) versus q/kT plot gives (phi) over bar (b0) values and Richardson constants (A*) as 1.108 and 0.634 eV and 31.42 and 23.83 A/cm(2) K-2, respectively, without using the temperature coefficient of the BH. The value of the effective Richardson constant of 31.42 A/cm(2) K-2 is very close to the theoretical value of 32 A/cm(2) K-2 for p-Si. As a result, the temperature dependence of the forward bias I-V characteristics of the Al/TiO2/p-Si (MIS) structure can be successfully explained on the basis of the TE mechanism with a double GD of the BHs. (C) 2008 American Institute of Physics.