A study on photo-induced crystallization in Ga₁₀Se₇₈Tl₁₂ thin films

This paper reports the photo-induced crystallization in glassy Ga₁₀Se₇₈Tl₁₂ thin films. The glassy nature of the bulk material was confirmed by non-isothermal differential scanning calorimetry measurements. The photo-induced crystallization in Ga₁₀Se₇₈Tl₁₂ films was done by exposing to light (using 2000 W tungsten lamp) at various illumination times under the fixed ambient temperature at 358 K. Virgin and photo-induced Ga₁₀Se₇₈Tl₁ thin films were characterized by X-rays diffraction, scanning electron microscopy, optical and electrical measurements. The photo-induced crystallization is associated to the change in structure of Ga₁₀Se₇₈Tl₁₂ thin films which initiated the significant change in the optical constants. The detailed examination of the optical absorption results indicated that the optical transition was indirect. The optical band gap of Ga₁₀Se₇₈Tl₁₂ thin films were decreased while the absorption and the extinction coefficients increased with the increase of illumination time. From dark conductivity results, the dark conductivities of thin films continuously heightened and the activation energy turned to be lower as increasing the illumination time. The lowering in optical band gap and activation energy might be due to the occurrence of photo crystallization with the increment of illumination time.