Experimental Demonstration of in Situ Stress-Driven Optical Modulations in Flexible Semiconducting Thin Films with Enhanced Photodetecting Capability

Flexible semiconducting thin films have a broad coverage of future competitive electronic and optoelectronic devices. Although the stress present in thin films has been long known to affect optical properties, the experimental verification of the optical modulations in flexible systems has not been available so far. Here, we propose an in situ deposition process of inducing intentional compressive or tensile stress in the flexible thin films, ultimately to define the actual level of optical bandgap and photosensitivity modulations using an example of narrow bandgap p-type semiconductor of PbS thin films. We experimentally and theoretically prove the stress dependency of bandgap changes from 1.43 to 1.73 eV in the strain range of -0.88 to +0.88%. A metal-semiconductor-metal device with compressive strain-induced PbS thin film exhibited a higher photoresponse compared to the unstrained ones, because of combined effects of favorable band edge positions as well as generation of a higher number of electron-hole pairs due to absorption of a wider range of photon energies owing to its lower bandgap.