Structural, optical and electrical properties of Sb doped and undoped AgIn_1 − xGa_xSe₂ and Ag(InGa)₅Se₈ thin films

Abstract

Antimony doped and undoped nanostructured thin films of AgIn1 − xGaxSe2 and Ag(InGa)5Se8 on optically flat soda lime glass substrates are prepared by a three stage co‐evaporation process. Energy dispersive analysis of X‐rays (EDAX) and X‐ray photoelectron spectroscopy in conjunction with atomic force microscopic technique and scanning electron microscopic technique are used, respectively, for compositional and surface morphological analysis of the films. X‐ray diffraction (XRD) data on the films are analysed to estimate the influence of antimony doping and indium replacement by gallium, on the structure of the films, by determining the anion–cation bond lengths and anion displacement in the thin films. The obvious dependence of band gap on the composition of the films establishes the possibility of band gap tailoring of the films. Low temperature optical absorbance measurements in the temperature regime 90–301 K are used for investigating the effect of doping on the temperature coefficient of band gaps of the films. Rutherford scattering spectra quantify the thickness of the films for conductivity (σ) measurements. The films exhibit n‐type conductivity with two linear regions in the ln(σ) versus temperature inverse graphs, which indicate a defect activated conduction and intrinsic conduction, respectively, in the near room temperature and high temperature regions.

Tin Incorporation in AgInSe2 Thin Films: Influence on Conductivity

“…The rate of decrease of temperature coefficient is 3.4 × 10 –5 eV/K and 7.2 × 10 –5 eV/K for n-type and p-type AIS:Sn films, respectively, and those values are slightly less than the reported value of 1.96 × 10 –4 eV/K for the undoped AgInSe 2 suggesting that Sn doping reduces the rate of gap shift with temperature. Our previous experiments also showed that Sb doping in Ag­(InGa)­Se 2 films reduced the temperature coefficient of band gap to 8.7 × 10 –5 eV/K . Here the parameters such as E F and γ could not be calculated for the present AIS films since the equations cannot be applied to very large values of Seebeck coefficient.…”

“…99.999% pure elements of Ag, In, Sn, and Se are thermally evaporated under vacuum ∼10 –5 mbar and deposited on heated glass substrates in a multisource vacuum coevaporation system by the modified Gunther’s three temperature technique; details are described elsewhere. − AIS thin films are prepared at a substrate temperature of about 598 ± 5 K while Sn is incorporated through a two-stage procedure in which Ag and In are evaporated at a substrate temperature of about 398 ± 5 K in the first stage and Ag and Sn are evaporated at 598 ± 5 K in Se atmosphere during the second stage. During the preparation of AIS and Sn incorporated AIS films, the Se flux is kept constant to avoid any unintentional variations in the Se pressure.…”