Hyperdoping-regulated room-temperature NO2 gas sensing performances of black silicon based on lateral photovoltaic effect

Black silicon co-hyperdoped with sulfur and nitrogen in different ratios is prepared by femtosecond laser-assisted chemical etching in the mixed atmosphere of SF6 and NF3 with varying gas pressure ratios. Their room-temperature NO2 gas sensing capability is studied systematically, in which the photocurrent as a readout signal is generated by the lateral photovoltaic effect of black silicon under an asymmetrical light illumination. These co-hyperdoped black silicon exhibits high response, fast response/recovery, ultrawide detection range from 29 ppb to 2000 ppm, excellent selectivity and acceptable long-term durability over 3 months. Moreover, NO2 gas sensing performances are effectively tuned or optimized by deliberately changing the co-doping ratio of sulfur and nitrogen, as different photovoltaic characteristics are induced by changes in morphology and structural defects resulting from different hyperdoping. Specifically, ultra-high relative gas response (~3955%@20 ppm NO2) and superior selectivity are obtained at the SF6/NF3 pressure ratio of 56/14, while faster response/recovery time (17 s/ 47 s@20 ppm NO2) and response photocurrent with a weaker disturbance by humidity are given by the samples with SF6/NF3 of 7/63 and 63/7, respectively. Therefore, such black silicon material has good potential to meet different application needs.