Impact of Al₂O₃ stress liner on two-dimensional SnS₂ nanosheet for photodetector application

Layered tin disulfide (SnS₂) nanosheets are gradually coming into people's vision as an emerging two-dimensional material for the potential application majority in optoelectronic field. We investigate a sample of ultra-thin SnS₂ nanosheets (∼5 nm) on SiO₂/Si substrates and the photodetectors performance based on it with and without high-k ALD-Al₂O₃ stress liner. By means of temperature-dependent Raman spectroscopy, both a red-shift of Raman frequency from 313.1 cm⁻¹ to 311.2 cm⁻¹ as well as a reduction of the first order temperature coefficient from −0.01232 cm⁻¹/K to −0.00895 cm⁻¹/K are measured. For device, compared to SnS₂ photodetector, Al₂O₃/SnS₂ photodetector shows enhancement with 7-times light current, 10-times responsivity, 25%-off rising time and 70%-off falling time under 365 nm illumination. The phenomena can be rationalized by factors that the SnS₂ sample suffers a tensile strain and passivation effect exerted by capped Al₂O₃ layer. Meanwhile, the first principle calculations assist the study from an angle of verification. The analogue stress treatment operated in this work improves the properties of SnS₂ and enhances the performances of SnS₂-based photodetectors, aiming at expanding the thin-film materials applications in optoelectronic devices.