Two diodes model and illumination effect on the forward and reverse bias I–V and C–V characteristics of Au/PVA (Bi-doped)/n-Si photodiode at room temperature

Abstract

The forward and reverse bias current–voltage (I–V), capacitance/conductance–voltage (C/G–V) characteristics of the fabricated Au/PVA (Bi-doped)/n-Si photodiode have been investigated both in dark and under 250 W illumination intensity at room temperature. The energy density distribution profile of Nss was extracted from the forward bias I–V measurements by taking the voltage dependence of effective barrier height (Φe) and Rs for photodiode both in dark and under 250 W illumination cases. The exponential growth of the Nss from midgap toward the bottom of the conductance band is very apparent for two cases. The obtained high value of n and Rs were attributed to the particular distribution of Nss at metal/PVA interface, surface and fabrication processes, barrier inhomogeneity of interfacial polymer layer and the form of barrier height at M/S interface. While the values of C and G/w increase Rs and Rsh decrease under illumination, due to the illumination induced electron–hole pairs in depletion region. The voltage dependent Nss profile was also obtained from the dark and illumination capacitance at 1 MHz and these values of Nss are in good agreement. In addition, the fill factor (FF) under 250 W illumination level was found as 28.5% and this value of FF may be accepted sufficiently high. Thus, the fabricated Au/PVA (Bi-doped)/n-Si structures are more sensitive to light, proposing them as a good candidate as a photodiode or capacitance sensor for optoelectronic applications in modern electronic industry.