Optical and Sensing Properties of Cu Doped ZnO Nanocrystalline Thin Films

R K Shukla,Nishant Kumar,Mamta Pandey,Akhilesh Pandey,Anchal Srivastava

doi:10.1155/2015/172864

Abstract

Undoped and Cu doped ZnO films of two different molarities deposited by spray pyrolysis using zinc nitrate and cupric chloride as precursors show polycrystalline nature and hexagonal wurtzite structure of ZnO. The crystallite size varies between 10 and 21 nm. Doping increases the transmittance of the films whereas the optical band gap of ZnO is reduced from 3.28 to 3.18 eV. With increment in doping the surface morphology changes from irregular shaped grains to netted structure with holes and then to net making needle-like structures which lends gas sensing characteristics to the films. Undoped ZnO shows maximum sensitivity at 400°C for higher concentration of CO2. The sensitivity of Cu doped sample is maximum at 200°C for all CO2concentrations from 500 to 4000 ppm.

Highlights

Zinc oxide, an environmentally safe and economic material, with wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) at room temperature [1,2,3] finds application in fabrication of various devices including ultraviolet (UV)light-emitters, varistors, transparent high power electronics, piezoelectric transducers, gas sensors, smart windows, and solar cells [4,5,6]
Some metals can assume a valency depending on their chemical surrounding, for example, any copper salt when doped in ZnO using organometallic solution can lead to varied oxidation states of Cu [9]
Nanocrystalline Cu doped ZnO films have been successfully deposited on glass substrates by spray pyrolysis and their structural and optical properties have been investigated

Summary

Introduction

An environmentally safe and economic material, with wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) at room temperature [1,2,3] finds application in fabrication of various devices including ultraviolet (UV). Light-emitters, varistors, transparent high power electronics, piezoelectric transducers, gas sensors, smart windows, and solar cells [4,5,6]. It is one of the most important II-VI compound semiconductors and its application in optoelectronics can be expanded by altering its band gap energy. Wet chemical techniques offer easy way for homogeneous doping of virtually any element in any proportion by merely adding it in some form of cationic solution. These techniques do not require high quality targets and/or substrates which are unavoidable in sputtering and PLD. Structural, optical, and morphological property of undoped and Cu doped ZnO thin films prepared by spray pyrolysis along with CO2 sensing [20] has been presented

Experimental

Findings

Conclusions