Strain engineering has been extensively explored for tailoring the material properties and, in turn, improving the device performance of semiconducting thin films. In particular, the effects of strain on the optical properties of these films have attracted considerable research interest, but experimental demonstrations in flexible systems have rarely been reported. Here, we exploited the variable optical properties of flexible ZnS thin films by imposing a controllable external compressive stress during a stretching-driven deposition process. This stress induced crystal anisotropy with an increase in tetragonality, which differs from that of the unstrained cubic ZnS thin films. The refractive index of the films was estimated by means of an envelope method using interference fringes. As a result, the reductions in the refractive index and optical band gap were observed by applying the stretching-driven strains with the resultant compressive stress. The modulated refractive index and its dispersion behavior were further investigated by employing a single-oscillator model to drive subsequent correlative parameters such as dispersion energy, oscillating strength, and high-frequency permittivity. As a proof of concept, an optical lens of ZnS was designed to confirm the effect of in situ stress-mediated optical modulation by detecting the variable focal length with stress.
Bibliographical noteFunding Information:
This work was financially supported by grants from the National Research Foundation of Korea (NRF-2016M3A7B4910151), Industrial Strategic Technology Development Program (#10079981), Korea Institute of Energy Technology Evaluation and Planning (no. 20173010013340) funded by the Ministry of Trade, Industry, & Energy (MOTIE) of Korea, and the Creative Materials Discovery Program by the Ministry of Science and ICT (2018M3D1A1058536).
All Science Journal Classification (ASJC) codes
- Materials Science(all)