Current transport mechanism in Al/Si3N4/p-Si (MIS) Schottky barrier diodes at low temperatures

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-insulator-semiconductor (Al/Si3N4/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80-300 K. By using the thermionic emission (TE) theory, the zero-bias barrier height PhiB0 calculated from I-V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C-V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a PhiB0 versus q/2kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of PhiBo = 0.826 eV and alphao = 0.091 V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln(Io/T2) - q2sigmao2/2(kT)2 versus q/kT plot gives PhiB0 and Richardson constant A as 0.820 eV and 30.273 A/cm2 K2, respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm2 K2 is very close to the theoretical value of 32 A/cm2 K2 for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/Si3N4/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density (NSS) profiles was determined from the forward I-V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.