High-selectivity NOx sensors based on an Au/InGaP Schottky diode functionalized with self-assembled monolayer of alkanedithiols

This work was devoted to fabricating high-selectivity NOx gas sensors based on an Au/InGaP Schottky diode. In order to enhance the sensing selectivity and sensing response, a self-assembled monolayer (SAM) of alkanedithiol was used to modify the Schottky contact with an S-Au covalent bond based on the self-assembled property and terminal functional group. The studied SAM/Au/InGaP Schottky diodes were fabricated by semiconductor processes and immersion treatment. The effects of the carbon number (CN) of SAM, the SAM immersion time, and immersion dithiol concentrations were comprehensively studied in this work. In addition, the selectivity and sensing performance of dithiol functionalized Au/InGaP Schottky diodes under different temperatures and NOx concentrations were studied for comparison. In order to obtain the optimal NOx sensing performance, cyclic voltammetry (CV) was employed to study the self-assembled performance of the dithiol monolayer on the Au surface. The sensing responses of 16.5 and 7.2 were obtained under 100 ppm NO2/N-2 and NO/N-2 at 30 degrees C, respectively, for the studied 1,10-decanedithiol (DDT)/Au/InGaP device. Moreover, compared to other sensing gases, the DDT/Au/InGaP sensing device showed high selectivity toward NOx gas. Furthermore, the theoretical first-order kinetic and thermodynamic theoretical analysis were consistent with the experimental transient and steady-state sensing results. Therefore, the studied SAM/Au/InGaP Schottky diode demonstrated promising results for NOx sensing applications.