Effects of sputtering pressure and annealing temperature on the characteristics of indium selenide thin films

Indium selenide is a significant two-dimensional lamellar semiconductor with excellent physical properties whose enormous potential utilization in optoelectronic devices has been practically hindered by the lack of suitable thin film deposition techniques. Herein, gamma-In2Se3 thin films were successfully fabricated from an InSe-target via magnetron sputtering combined with subsequent annealing process. The effects of sputtering pressure and annealing temperature on the characteristics of as-deposited thin films were investigated. The x-ray diffraction (XRD) patterns reveal that the pristine thin films are amorphous in nature, whereas transform into polycrystalline and are identified as gamma-In2Se3 phase after annealing treatment. The growth mechanism of as-deposited layers combines a two-dimensional lateral growth and a three-dimensional island growth. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images indicate that all the samples show uniform and compact structures with no evident holes and crevices. The UV-vis-NIR spectrophotometer was employed to measure the optical transmittance and band gap of the synthesized thin films. The results show an obvious decrease in the band gap from 2.56 eV to 1.88 eV with annealing temperature increased from 400 degrees C to 600 degrees C, respectively. In addition, the difficult reasons for preparing monophase InSe thin films by magnetron sputtering method were discussed. These intriguing findings in this study may shed light on the growth of indium selenide thin films with well-crystallized and high quality.