The Impact of Gate Recess on the H₂ Detection Properties of Pt-AlGaN/GaN HEMT Sensors

The present work reports on the hydrogen gas detection properties of Pt-AlGaN/GaN high electron mobility transistor (HEMT) sensors with recessed gate structure. Devices with gate recess depths from 5 to 15 nm were fabricated using a precision cyclic etching method, examined with AFM, STEM and EDS, and tested towards H2 response at high temperature. With increasing recess depth, the threshold voltage ( VTH ) shifted from -1.57 to 1.49 V. A shallow recess (5 nm) resulted in a 1.03 mA increase in signal variation ( Δ IDS ), while a deep recess (15 nm) resulted in the highest sensing response ( S ) of 145.8% towards 300 ppm H2 as compared to reference sensors without gate recess. Transient measurements demonstrated reversible H2 response for all tested devices. The response and recovery time towards 250 ppm gradually decreased from 7.3 to 2.5 min and from 29.2 to 8.85 min going from 0 nm to 15 nm recess depth. The power consumption of the sensors reduced with increasing recess depth from 146.6 to 2.95 mW.