Current transport mechanism in Al/Si 3N 4/p-Si (MIS) Schottky barrier diodes at low temperatures

Abstract

The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–insulator–semiconductor (Al/Si 3N 4/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 Φ B0 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 Φ B0 versus q/2 kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ Bo = 0.826 eV and α o = 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( I o/ T 2) − q 2 σ o 2/2( kT) 2 versus q/ kT plot gives Φ B0 and Richardson constant A * as 0.820 eV and 30.273 A/cm 2 K 2, respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm 2 K 2 is very close to the theoretical value of 32 A/cm 2 K 2 for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/Si 3N 4/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 ( N SS) profiles was determined from the forward I– V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.