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

Abstract

Abstract 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 × 10 16 c.c. −1 for the ZnO NW thin film. The ideality factor ( n ) was found to decrease, while the barrier height ( φ 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.