Composition dependent structural phase transition and optical band gap tuning in InSe thin films

Bulk alloys of In(x)Se(100-x) (x = 5, 10, 20, 30, 40 and 50) are prepared using melt quenching technique. Thin films having thickness ~750 nm of these prepared bulk alloys are fabricated using thermal evaporation technique on glass substrate. The as-deposited In(x)Se(100-x) thin films with x ≤ 40 are amorphous and In(50)Se(50) thin film is crystalline in nature verified from X-ray diffraction (XRD). The change in morphology of deposited thin films with indium content also verifies structural phase transition and found that the phase transition started with x = 40 which is not detected in XRD pattern. The drastic change in transmission is found with 50% indium content. In(50)Se(50) thin film has less than 30% transmission whereas other films are highly transparent. Optical band gap is calculated using Tauc's plot and decrease in optical band gap is observed with indium content. The variation of optical band gap from 1.88 eV to 1.12 eV is achieved with indium content of 5%–50%. The structural transition and change in optical band gap depict that InSe thin films are potential candidates in various technological applications.