Effect of Dopant Concentration and Solution pH on the Structural and Optical Properties of Electrodeposited Manganese-Doped Zinc Selenide Thin Films

Abstract

The study has been carried out to investigate the influence of manganese concentration and solution pH on the structural and optical properties of electrodeposited Mn-doped ZnSe thin films. The study adopted an experimental research type using lab apparatus to grow and ZnSe/Mn thin films.Manganese doped ZnSe thin films have been deposited on well cleaned fluorine-doped tin oxide (FTO) coated conducting glass substrates at room temperature via two-electrode potentiostatically electrodeposition technique. All deposition was carried out at room temperature of 25oC. Prepared solutions of Mn(NO2)3.5H2O, ZnSO4.7H2O and hydrogen selenide as sources of  Mn2+, Zn2+and Se2-  ions respectively were used. The Mn concentrations have been varied by varying the molar concentration of Mn (NO2)3.5H2O in the solution as 0.0, 0.1, 0.2 and 0.3 mol %. Ammonia (NH3) solution has been used to adjust the pH of the solution (as pH 7.0, 7.5, 8.0 and 8.5). The samples thickness has been obtained electromechanically by a profilometer measurement. X-ray diffraction studies revealed eight (8) diffraction peaks oriented along (110), (101), (200), (211), (220), (310), (301) and (321) planes, indicating that all the deposited films were polycrystalline in nature with mixture of cubic zinc blende and hexagonal structures with the most preferred orientation along (211) plane. The average crystallite size calculated increases as the Mn concentration and solution temperature increases. Optical studies revealed a direct band gap transition with the energy value decreases (as 3.56, 3.43, 3.39 and 2.92 eV) as the Mn contents increases, and increases (as 3.39, 3.91, 3.96 and 3.88 eV) with increase in the solution pH. The optical conductivity of the grown thin films was in the range of 2.87 – 3.32 x1014 s-1. The synthesized thin films could find potential application in photo sensing, optoelectronic and hetero-junction solar cells devices.