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 H
₂
response at high temperature. With increasing recess depth, the threshold voltage (
${V}_{\textit {TH}}$
) shifted from −1.57 to 1.49 V. A shallow recess (5 nm) resulted in a 1.03 mA increase in signal variation (
$\Delta {I}_{\textit {DS}}$
), while a deep recess (15 nm) resulted in the highest sensing response (
${S}$
) of 145.8% towards 300 ppm H
₂
as compared to reference sensors without gate recess. Transient measurements demonstrated reversible H
₂
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.