Density impact of doped ZnO discs on the structural, electrical and optical properties in the ohmic region

Abstract

The influence of different densities of doped ZnO discs on their structural, electrical and optical properties has been studied in this work by measuring the average grain size, resistivity, critical frequency, critical capacitance and energy band gap as functions of density. The microstructure of ZnO material has been investigated by a combination of X-ray diffractometry (XRD) and analytical electron microscopy (SEM, EDX). Doped ZnO has a large number of grains and grain boundaries, which are observed to be very disordered. Every sample has a different densities depending on the different grain size, which had a major effect on the properties of ZnO. There are also a considerable number of pores which depend on the size and the shape of grains. The voltage (V) against the current (I) curves, revealed a high linear (ohmic) relationship, mainly in sample B4, which represented the highest density value (5.486 g/cm3), highest resistivity value (0.46 GΩ.cm), and maximum capacitive critical frequency (48.23 MHz). However, the critical capacitance value (1.21 nF) decreased at a higher density, which could be due to the high traps. The photoluminescent measurements showed that the doped ZnO had a strong ultraviolet emission at around 381nm and a weak red emission around 650 nm. The results from PL spectroscopy revealed the band gap energy of ZnO (ranged from 3.25 eV to 3.29 eV), which increased gradually with density, depending on the grain boundaries barrier.