High-Performance GeS Thin Film Photodetectors Obtained via Sulfurization and Boron Doping

The next-generation photodetectors require materials that offer high performance in terms of responsivity and detectivity, especially in the visible spectrum. The two-dimensional semiconductors have recently emerged as promising materials for use in these devices due to their tunable optoelectronic properties. However, it is still a challenge to achieve a competitive performance with conventional semiconductors. In this study, we investigate the effects of sulfurization and doping on the performance of GeS thin-film photodetectors. We synthesized the pristine GeS, sulfurized GeS (GeS(S)), and boron-doped sulfurized GeS (GeS:B(S)) films using a rapid thermal evaporation method, which allowed us to obtain films exhibiting a pure GeS phase with a dominant hkl (100) orientation, characteristic of the layered structure. The structural, optical, and electrical properties of the films were characterized as functions of sulfurization and doping. The results show that sulfurization significantly enhanced the photocurrent, while boron doping provides additional improvements in responsivity and detectivity but at the expense of slower response times, reflecting the responsivity and speed trade-off typical for photoconductors. A lateral photoconductor device was fabricated using interdigitated array (IDA) platinum electrodes operating on the photoconductive effect. The device based on sulfurized and boron-doped GeS demonstrated a high responsivity of 22.68 A/W and a detectivity of 1.38·1013 Jones under 532 nm illumination, with switching times around 500 μs. These findings indicate that sulfurization and boron doping are promising strategies to improve the performance of GeS thin-film visible-light photodetectors, making them reasonable candidates for high-performance optoelectronic applications. To the best of our knowledge, this work also shows one of the first experimental studies investigating boron doping in GeS thin films, opening perspectives for the further tuning of their optoelectronic properties.