Naser Qamhieh
United Arab Emirates University, UAE
Title: Optical and electrical characterization of Co doped Ge-Sb-S films
Biography
Biography: Naser Qamhieh
Abstract
Thin films of amorphous Germanium antimony sulfide (Ge30Sb10S60) doped with cobalt (Co) have been deposited on glass substrates by thermal evaporation technique. The composition and amorphous structure of the deposited films have been characterized by X-ray diffraction and energy dispersive X-ray analysis (EDX) techniques. Optical transmission spectra measured by UV-VIS spectrophotometer showed that Co-doped Ge30Sb10S60 have 2.0 eV optical band gap. Raman spectroscopy was used to characterize the composition and phase structure of the prepared film and shows a wide band spectrum from 300 to 410 cm-1 centered at 355 cm-1. The Raman shift peaks at 325 cm-1 and 350 cm-1 are assigned to the bond stretching mode Sb-S and Ge-S, respectively. The capacitance and conductance versus voltage measurements were performed at different temperatures. The results show a slight increase in the capacitance with temperature and it reaches a maximum value around 150 oC and eventually it becomes negative. This behavior is interpreted in terms of the nucleation-growth process and the thermally activated conduction process with measured activation energy of 0.79 eV. This value of activation energy together with the measured optical gap indicates that the Fermi level is unpinned in the gap which could be attributed to gap states induced by cobalt doping.