Enhanced detection of NO2 with recessed AlGaN/GaN open gate structures

Recessing of the open gate region of AlGaN/GaN heterostructures is shown to dramatically enhance the sensitivity of these devices to surface interactions. This is demonstrated by NO2 exposure under humid conditions. NO2 adsorption at the open gate region leads to a decrease in two-dimensional electron gas conductivity, which we attribute to the interaction of NO2 with surface donor states. We find that the recessing enhances the sensitivity to NO2 by almost three orders of magnitude. This may also be used to improve the sensitivity of other (bio)chemical sensors based on AlGaN/GaN. Furthermore, the effect of humidity on the NO2 response is investigated.