Improvement in performance of SnSe-based photodetectors via post deposition sulfur diffusion

Abstract

The work represents an enhancement in the photodetector properties of thermally evaporated SnSe thin films through both annealing and sulfurization processes. X-ray diffraction analysis showed the formation of SnSe1-xSx alloy with a graded composition that was more S-rich near the surface when the sulfurization process was applied at 350 °C. Scanning electron microscopy results indicated that increasing the annealing temperature from 300 ºC to 350 ºC changed the microstructure greatly. When the sulfurization temperature was increased from 300 ºC to 350 ºC, the direct band gap of SnSe thin films decreased from 1.38 eV to 1.30 eV while the indirect band gap reduced from 0.91 eV to 0.71 eV. Raman spectra also confirmed the development of phase of SnSe1-xSx for the sulfurized sample at 350 °C. Photocurrent-time curves of devices fabricated on all films demonstrated that sulfurization at high temperature increased the photocurrent values. It was further determined that devices made on sulfurized layers had smaller rise/fall times of 2.57/2.33 s compared to those fabricated on non-sulfurized films. The best responsivity and detectivity values were achieved as 2.07 × 10−1 A/W and 1.19 × 107 Jones, respectively, for photodetectors fabricated on layers sulfurized at 350 °C.