Incorporation of tin in nanocrystalline CdSe thin films: a detailed study of optoelectronic and microstructural properties

Abstract

Tin-doped nanocrystalline CdSe thin films were deposited onto glass substrate by simple chemical bath deposition technique. The films obtained were uniform and had good adherence to the substrate. The influence of Sn (0–5%) doping on the optical, photoluminescence, electrical, morphological, compositional and structural properties of the films was investigated. The optical absorption studies revealed that the optical band gap of the films varied from 2.62 eV for nano CdSe to 2.50 eV for 5% Sn:CdSe. These films are appropriate for application in different optoelectronics devices due to band gap tunability property. To analyze photoluminescence properties, the films were excited by UV (235 nm) and almost green spectrum was emitted by the films. It is observed that the low temperature resistivity of the thin films was in the range 107–104 Ω cm and also found to decrease with Sn concentration, as resulted from the dc two probe measurements. Activation energy was also calculated. Noticeable changes were observed in the optical and electrical properties of CdSe thin films due to the presence of Sn dopant. Surface morphology study using TEM/SEM showed almost uniform distribution of spherical grains. The elemental composition study using energy dispersive spectroscopy (EDAX) confirms the existence of the desired elements. X-ray diffraction pattern indicated that the formed structure is cubic with most prominent peak at (111). Some important structural parameters such as lattice constant, crystallite size, strain, dislocation density and number of crystallites per unit area were calculated and presented.