Gaussian distribution of inhomogeneous barrier height in Al/SiO2/p-Si Schottky diodes

The forward and reverse bias current-voltage (I-V) characteristics of Al/SiO2/p-Si (metal-insulator-semiconductor) type Schottky diodes (SDs) were measured in the temperature range of 200-400 K. Evaluation of the experimental I-V data reveals a decrease in Phi(B0) and R-s but an increase in n, with a decrease in temperature. To explain this behavior of Phi(B0) with temperature, we have reported a modification which included n and the tunneling parameter alpha chi(1/2)delta in the expression of reverse saturation current I-0. Thus, a corrected effective barrier height Phi(B eff)(I-V) vs T has a negative temperature coefficient (alpha approximate to-5x10(-4) eV/K), and it is in good agreement with alpha=-4.73x10(-4) eV/K of Si band gap. Such behavior of R-s estimated from Cheung's method could be expected for semiconductors in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures. Also, there is a linear correlation between Phi(B0)(I-V) and n due to the inhomogeneities of the barrier heights (BHs). The conventional activation energy (E-a) plot exhibits nonlinearity below 320 K with the linear portion corresponding to E-a of 0.275 eV. An A(*) value of 1.45x10(-5) A cm(-2) K-2,which is much lower than the known value of 32 A cm(-2) K-2 for p-type Si, is determined from the intercept at the ordinate of this experimental plot. Such behavior is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of BHs due to BH inhomogeneities that prevail at the interface. We attempted to draw a Phi(B0) vs q/2kT plot to obtain evidence of a GD of the BHs, and the values of (Phi) over bar (B0)=1.136 eV and sigma(0)=0.159 V for the mean BH and standard deviation at zero bias have been obtained from this plot. Therefore, the modified ln (I-0/T-2)-q(2)sigma(2)(0)/2k(2)T(2) vs q/kT plot gives (Phi) over bar (B0) and A(*) values of 1.138 eV and 37.23 A cm(-2) K-2, respectively, without using the temperature coefficient of the BH. This A(*) value of 37.23 A cm(-2) K-2 is very close to the theoretical value of 32 A K-2 cm(-2) for p-type Si. Therefore, it has been concluded that the temperature dependence of the forward bias I-V characteristics of the Al/SiO2/p-Si SDs can be successfully explained based on the thermionic emission mechanism with a GD of the BHs. (C) 2008 American Institute of Physics.