Effects of post-deposition processing on microstructural properties of cadmium selenide thin films grown from solution

Laboratoire des Semiconducteurs et d'Énergie Solaire, Département de Physique, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar, Dakar-Fann, Senegal

Corresponding author: iyoum@ucad.sn

Received: 28 September 2001
Revised: 8 October 2002
Accepted: 2 April 2003
Published online: 20 June 2003

Abstract

Thin films of cadmium selenide (CdSe) were grown by the chemical bath deposition (CBD) technique. The effects of the common grain growth promoter, cadmium chloride (CdCl₂) and annealing on the films were investigated. X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS) measurement techniques are used to determine the crystalline structure, surface morphology and composition of the as-deposited and annealed films. Noticeable changes in XRD patterns were observed on the annealed films. The as-deposited films of poor crystalline quality are transformed into crystalline hexagonal phase of CdSe. The annealing and CdCl₂ treatment affects the grain growth, which is stronger for the CdCl₂ treated samples. The optical properties of the films were investigated by optical transmittance and photoluminescence (PL) spectroscopy. The optical band gaps of the films are estimated using the optical transmittance measurements. A decrease in the band gap is observed for the annealed films with or without CdCl₂ addition. Photoluminescence peak intensity due to the near band edge luminescence is found to increase with annealing and it increases pronouncedly by annealing with CdCl₂ treatment. This effect can be attributed to the enhancement of the crystallinity of the films. Nevertheless, films annealing after CdCl₂ treatment resulted in selenium vacancies, which display a band emission centred at 1.4 eV.