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.