Surface electronic property of SiC correlated with NO2 adsorption

Abstract

Correlations between surface electronic properties of SiC and NO2 adsorption were investigated using electrostatic force potentiometry. It was observed that surface work function (SWF) of both 6H and 3C–SiC changes significantly with NO2 adsorption. Measurements on semi-insulating 6H–SiC revealed that the Si face has higher sensitivity toward NO2 molecules than C face producing more change in SWF due to NO2 adsorption, which can be related with the difference in their surface free energies. For an n+-doped 6H–SiC, the SWF of the C face was found to increase much more than the Si face, showing correspondingly higher NO2 sensitivity. Upon exposure to superbandgap ultraviolet (UV) illumination, the surface band bending of both the faces was found to increase for undoped 6H–SiC, which resulted in enhanced sensitivity to NO2 adsorption. Measurements on doped SiC also supported similar correlations, although the surface band bending initially decreased under UV illumination. Our results indicate that adsorption of NO2 on 6H–SiC surfaces strongly depends on the surface band bending, with lower band bending resulting in decreased sensitivity, and vice versa. Faster desorption of NO2 molecules through UV exposure was observed for undoped 6H–SiC but not for the doped one. An adsorption model for NO2 has been proposed to explain the experimental observations.