Improvement of opto-electro-structural properties of nanocrystalline CdS thin films induced by Au9 + ion irradiation

Abstract

CdS based thin film solar cells are potential for achieving high conversion efficiencies. In the present study, CdS thin films are prepared using chemical bath deposition technique and their structural, optical and electrical properties are improved under the effect of 120MeV Au9+ ions irradiation at room temperature (RT) and liquid nitrogen temperature (LNT). The films are characterized by glancing angle X-ray diffraction (GAXRD), Field emission scanning electron microscopy (FESEM), Rutherford backscattering spectrometry (RBS), Hall measurements, UV–vis and Raman spectroscopy techniques. GAXRD study confirms that the pristine and irradiated films at lower fluences (1×1012ionscm−2) at RT belong to the cubic crystal system with preferential growth along (111) plane and the cubic system of pristine film is transformed to the hexagonal structure at higher fluences irradiation (5×1012 to 1×1013ionscm−2). The FESEM image of pristine sample reveals that the surface of CdS thin films contains nano flakes structures. The modification of the surface morphology of the film due to the ion irradiation with different fluences is studied. The thickness and chemical composition of films are analyzed by RBS which detects the presence of oxygen in the irradiated samples at RT and LNT. Optical band gap of pristine film is decreased from 2.95eV to 2.56eV due to irradiation of Au9+ ions with the fluence of 1×1013ionscm−2 (RT). The Raman peak position (1LO) is shifted to higher wave number upon increase of irradiation fluence at RT and LNT. The resistivity (ρ) of 7.89 Ω cm and charge carrier concentration (n) of 1.640×1015cm−3 have been achieved in the CdS film irradiated with the fluence of 1×1013ionscm−2 at RT.