Preparation of n-type Copper Gallium Selenide thin films by tin doping and analysis of its structural, electrical, optical and transport properties

This paper reports doping with tin as a successful technique to induce n-type conductivity in Copper gallium selenide, which is established as an inflexibly p-type material, thus opening up new avenues in its optoelectronic applications. The conductivity type has been confirmed by multiple characterizations employing hot probe, Hall and thermopower measurements. The structure, composition and morphology of the films are well characterized by X-Ray Diffraction, Raman Spectra, Energy Dispersive Analysis by X-Rays, X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy. Optical analysis gives the fundamental bandgap as 1.55 +/- 0.03eV which is lower than that of undoped CGS. The conductivity mechanisms prevailing in the low temperature range of 100-170 K is the Seto's grain boundary model with the barrier height estimated as 80 +/- 4 meV and Arrhenius thermal activation in the range of 185-300 K with activation energy of 120 +/- 6 meV attributed to Se vacancies. The activation energy calculated in the temperature range 350-473 K is 470 +/- 28 meV which is due to tin on gallium site donor level formation. Thus achievement of n-type conductivity is attributed to the uncompensated donor level formations when Sn4+ takes the position of Ga3+ and to Se vacancies.