Investigations on the preparation and characterization of pure and rare earth doped ZnO nanorods and thin films

Abstract

Zinc oxide (ZnO) has attracted resurgent interest as an electronic material for numerous applications. With a direct gap of 3.4 eV at room temperature, ZnO is a wide band gap semiconductor that emits light in the near-UV region of the spectrum. ZnO is important for its multi-functional properties (semiconducting, magnetic, piezoelectric etc.) for electronic and optoelectronic applications. One of the key requirements for many of these applications is the doping of ZnO with various elements for enhancing and controlling its electrical, optical and multifunctional properties. Rare earths (RE) doped semiconductors have long been the topic of research owing to their prominent and desirable optical and magnetic properties. Spectroscopic ellipsometry studies were carried out to accurately determine the thickness and the optical constants of Sm and Dy doped ZnO thin films. It was observed that the optical constants of Sm and Dy doped ZnO films are related to the film composition. From the absorption studies, the band edge position of Sm doped ZnO is observed to be shifted towards higher wavelength side. The observed decrease in band gap upon increasing Sm concentration is attributed to the formation of Sm impurity band into the ZnO energy bands. Photoluminescence spectra of Sm doped ZnO show that the intensity of the blue and green emission is enhanced with increasing Sm doping. Optical transmittance studies confirmed that the films are fully transparent in the visible region. The NBE emission shifts towards the lower wavelength side upon increasing dysprosium concentration. This behavior could be explained with the Burnstein-Moss effect (Fermi level gets lifted into the conduction band of the degenerated semiconductor when ZnO thin films were doped with Dy, which leads to blue shift. The present investigation reveals that the rare earth dopants have significant influence on the structural and optical properties of ZnO nanostructures.