Optical and Structural Properties of Chemical Bath Deposited Cadmium Sulphur Selenide (CdS1–xSex (0 ≤ x ≤ 1)) Thin Films

Isaac Nkrumah,David U Ngbiche,Robert K Nkum,Mark Paal,Francis K Boakye,Francis K Ampong

doi:10.4236/ojapps.2019.911064

Abstract

The tuneable band gap property of Cadmium-sulphur-selenide (CdS1–xSex) thin film makes it an appropriate material for a wide range of optoelec-tronic applications and this has aroused a lot of interest. In this paper, we report the study of Cadmium-sulphur-selenide (CdS1–xSex) thin films, successfully grown on commercial glass slide substrate by the chemical bath deposition technique. The effect of selenium content (x value) on the structural, and some optical properties have been studied. The bath solution contained cadmium acetate dehydrate [Cd(CH3COO)2·2H2O], so-dium selenosulphate [Na2SeSO3] and thiourea [CS(NH2)2] were used as the sources of Cd2+, Se2﹣ and S2+, respectively. Tartaric acid (C4H6O6) was used as a complexing agent. The pH of the solution was adjusted to 12 by drop-wise addition of ammonia. The bath temperature was kept at 90°C for a deposition time of 1 hour. Post deposition annealing processes of the thin films were performed in a furnace at a temperature of 400°C for two hours. Both as-deposited and annealed films were characterised by Powder X-Ray Diffraction, Scanning Electron Microscopy, UV-Visible Optical Absorption Spectroscopy and Energy Dispersive X-Ray Analysis. Optical absorption data analysis indicates that direct allowed transitions occur in the films. The band gap of the as-deposited CdS1–xSex decreased linearly from 2.34 eV to 1.48 eV, with increasing selenium content, and in the annealed samples, decreased from 1.84 eV to 1.36 eV. X-ray diffrac-tion measurements revealed, that pure CdS, and CdSe had mixed hexago-nal and cubic phases. All the remaining ternary compounds were com-posed of cubic CdS and hexagonal CdSe phases. The annealed samples showed well defined and more intense peaks, suggesting an improvement in crystallinity. The average grain size increased slightly with increasing selenium content. SEM micrographs showed that the films were compact with a smooth texture and good coverage across the entire area of the substrate.

Highlights

Extensive studies have been carried out on CdS and CdSe semiconducting compounds, either as thin films or nanoparticles
We report the study of Cadmium-sulphur-selenide (CdS1–xSex) thin films, successfully grown on commercial glass slide substrate by the chemical bath deposition technique
SEM micrographs showed that the films were compact with a smooth texture and good coverage across the entire area of the substrate

Summary

Introduction

Extensive studies have been carried out on CdS and CdSe semiconducting compounds, either as thin films or nanoparticles This is due to the interesting properties they exhibit such as, high absorption coefficients in the visible and infrared part of the electromagnetic spectrum, good electrical properties (e.g. carrier mobility and lifetime) and the possibility of obtaining adjustable n- or p-type conductivity by doping [1]. The formation of a homogeneous solid solution over the entire compositional range (0 ≤ x ≤ 1), by the combination of these two compounds allow the production of very interesting ternary CdS1–xSex systems [2] Such mixed compositions are of interest mainly because they allow tuning of the semiconductor properties (most commonly bandgap and, spectral sensitivity). These are considered very important for a wide range of optoelectronic applications

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