Highly transparent and luminescent nanostructured EU2O3 doped ZnO films

R Sreeja Sreedharan,C Sudarsanakumar,V Ganasan,Radhakrishna Prabhu,V P Mahadevan Pillai

doi:10.1088/1757-899x/64/1/012027

Abstract

Zinc oxide is a wide, direct band gap II-VI oxide semiconductor. Pure and Eu-doped ZnO films are prepared by RF Magnetron sputtering at different doping concentrations (0.5, 1, 3 and 5 wt %). The films are annealed at 500 0C in air for two hours. The structural, morphological and optical properties of the films are characterized using XRD, micro-Raman, AFM, UV-Visible and photoluminescence spectroscopy. The thickness of the films is measured using stylus profilometer. XRD analysis shows that all the films are highly c-axis oriented exhibiting a single peak corresponding to (002) lattice reflection plane of hexagonal wurtzite crystal phase of ZnO. The micro-Raman spectra analysis reveals the presence of E2 high mode in all the samples which is the intrinsic characteristic of hexagonal wurtzite structure of ZnO. The appearance of LO modes indicates the formation of defects such as oxygen vacancies in the films. AFM micrographs show uniform distribution of densely packed grains of size with well defined grain boundaries. All the films exhibit very high transmittance (above 80%) in the visible region with a sharp fundamental absorption edge around 380 nm corresponding to the intrinsic band edge of ZnO. All the films show PL emission in the UV and visible region.

Highlights

Zinc Oxide (ZnO) is a wide, direct band gap (Eg = 3.3 eV at room temperature) II-VI oxide semiconductor with a large excitonic binding energy of 60 meV at room temperature, making it suitable for exciton-related applications.1-2 It is highly transparent in the visible region with a sharp cut-off around 380 nm
The X-ray diffraction analysis shows that all the films present a single sharp intense peak corresponding to (002) lattice reflection plane of hexagonal wurtzite structure of ZnO (JCPDS card No-75-0576)11presenting a single crystalline like structure with c-axis orientation due to lowest surface free energy of (002) lattice reflection plane.12-There is a slight enhancement in intensity of (002) peak with moderate Eu2O3 doping concentrations
The stress introduced due to the mismatch of ionic radii of Zn (Zn2+ = 0.74Ao) and Eu (Eu3+ = 1.07Ao) can be the reason for enhanced FWHM of the (002) peak in Eu2O3 doped ZnO films compared to the undoped ZnO film

Summary

1.Introduction

The band structure and optical properties of ZnO are similar to GaN, which is commonly used for the fabrication of photonic devices in the UV range Owing to these characteristics, ZnO has attracted much attention for a variety of applications in the field of short wavelength optoelectronic devices such as blue and ultraviolet light emitters, laser diodes, phosphorescent display and photo detectors.. ZnO has attracted much attention for a variety of applications in the field of short wavelength optoelectronic devices such as blue and ultraviolet light emitters, laser diodes, phosphorescent display and photo detectors.3 It is widely used as transparent conducting electrodes, window material, flat panel displays, gas sensors etc.. This paper reports the preparation of Eu-doped ZnO films by RF magnetron sputtering and their structural, morphological and optical characterisation using various techniques such as XRD, microRaman, AFM, UV-Visible and photoluminescence spectroscopy. Photoluminescence spectra of the samples are recorded using Horiba Jobin Yvon Fluralog III modular spectro flourometer

XRD Analysis

Micro-Raman analysis

Conclusion