Electrical characteristics and rectification performance of wet chemically synthesized vertically aligned n-ZnO nanowire/p-Si heterojunction

摘要

Vertically well-aligned n-ZnO nanowire (NW) thin films were deposited onto p-Si substrates by a two-step wet chemical technique to form a p-n heterojunction diode. The morphological and structural characteristics of the ZnO NW performed by scanning electron microscopy (SEM) and x-ray diffraction (XRD) revealed well-aligned h-ZnO NW with a wurtzite structure. A direct optical band gap of 3.30 eV was calculated from the transmittance trace obtained using a UV-VIS-NIR spectrophotometer. The electrical characteristics of the heterojunction diode were studied by capacitance-voltage (C-V) measurement at room temperature, and current-voltage-temperature (I-V-T) measurements performed in the 300-400 K range. The C-V measurements yield a carrier concentration of 1.3 x 10(16) c.c.(-1) for the ZnO NW thin film. The ideality factor (n) was found to decrease, while the barrier height (phi(b0)) increased with the increase in temperature, when calculated using a thermionic emission model from the non-linear I-V-T plots. The series resistance (R-s) calculated by the Cheung-Cheung method decreased with the increase in temperature. The mean barrier height (0.718 eV) and modified Richardson constant (28.4 A cm(-2) K-2) calculated using a Gaussian distribution of barrier heights (considering barrier height inhomogeneity) were closer to the theoretical value than those calculated from the linear approximation of the ln(I-s/T-2) versus 1000/T plot. The variation of the density of interface states with interface state energy was also studied. The n-ZnO NW/p-Si heterojunction diode performed very good half wave rectification in the frequency range 50 Hz-10 kHz, when a sinusoidal ac voltage of amplitude 4.5 V was applied across it.