Electronic and surface properties of H-terminated diamond surface affected by NO2 gas

Hydrogen-terminated diamond surface exhibits p-type conductivity during its exposure to air. To investigate this phenomenon, we examined the influence of different gases on the surface conductivity. Exposure to NO₂ gas resulted in the biggest increase in conductivity, while H₂O vapor decreased the surface conductivity. Moreover, even very low concentrations of NO₂ molecules in air increased the hole sheet concentration, and with increasing NO₂ concentration, the hole sheet concentration increased up to 2.3 × 10¹⁴ cm^? 2 (at 300 ppm NO₂). This increase of hole sheet concentration was observed during exposure to NO₂ gas and simultaneous adsorption of NO₂ molecules on the diamond surface, while it decreased when the exposure stopped and NO₂ molecules desorbed from the surface. X-ray photoelectron spectroscopy investigation showed upward band bending and partial oxidation of the hydrogen-terminated surface after exposure to air and NO₂. FETs exposed to NO₂ gas exhibited lower source and drain resistances, which led to a 1.8-fold increase of maximum drain current, transconductance increased 1.5-fold and maximum frequency of oscillation increased 1.6-fold.