The effects of doping and temperature on properties of electrochemically deposited Er3+ doped ZnSe thin films

Abstract

Zinc Selenide (ZnSe) is a binary chalcogenide with band gap (Eg) of about 2.70 eV. Doping is used to tune band gap in order to optimize electrical and optical properties of thin films. The aim of this work was to determine the effects of doping and deposition temperature on the properties of erbium doped zinc selenide (Er3+;ZnSe). Undoped ZnSe and Er3+;ZnSe (1–4%)] were deposited at room temperature and at deposition temperatures between 40 °C and 100 °C on fluorine doped tin oxide (FTO) glass by electrochemical technique. The effects of doping and deposition temperature on the crystal structure, morphology, optical and electrical properties of the deposited ZnSe were investigated. XRD results showed that both undoped and Er3+;ZnSe were crystalline in nature with strong orientation along (111) and (311) directions. Peak intensity of Er3+;ZnSe decreased from Er1% to Er3% as doping concentration increased and then increased as concentration increased to 4%. The peaks were indexed to the cubic structure of ZnSe thin film with Er2% showing the highest purity. The UV–vis result revealed that the samples deposited at higher deposition temperatures [Er4%(80 °C) and Er4%(100 °C)] showed lower transmittance. Undoped ZnSe had band gap of 2.75 eV which approximated the bulk value. The band gap was observed to decrease as deposition temperature increased. The films deposited at room temperature had wider band gap (2.9 eV–2.61 eV) than those deposited above room temperature (2.21 eV–1.69 eV). The SEM micrograph revealed that low doping concentration (Er1%) had no effect on morphology. Er2% had the highest resistivity of about 8.41 × 103 Ωcm and lowest conductivity of 1.19 × 10−4 Ωcm−1. Doping and deposition temperature thus affected most of the investigated properties. Er3+;ZnSe (Er1% - Er4%) and Er4% (40 °C) – Er4% (100 °C) find applications as solar cell buffer layers and absorbers respectively.