Chemically gated AlGaN∕GaN heterostructure field effect transistors for polar liquid sensing

Al Ga N ∕ Ga N heterostructure field effect transistors are investigated to monitor the polarity of liquid molecules by exposing the unmetallized gate region between source and drain contacts to chemicals with dipole moments (μ) in the range of 1.6–3.96D. The results show that the channel current can be quantitatively modulated by the magnitude of μ of tested polar molecules. At room temperature, in comparison with the value in air, the channel current density drops from 13.9to7.15mA∕mm with chlorobenzene (μ=1.6D) or to 1.35mA∕mm with diemthyl sulfoxide (μ=3.96D) at a source-drain bias (VDS) of 10V. A linear fitting shows that the current slope is around −1.8mA∕(mmD). Dynamic response of the channel current indicates excellent reversibility of devices. The response time of devices is in the range of 0.1–16s for the chemicals tested in this work.