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 FB0 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 FB0 versus q/2kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of FBo = 0.826 eV and ao = 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) q2so 2/2(kT)2 versus q/kT plot gives FB0 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