Recessed gate Pt-AlGaN/GaN HEMT H2 sensor

This work reports on the fabrication and characterization of recessed gate Pt-AlGaN/GaN HEMT H2 sensor. The device with partially etched AlGaN layer was obtained by cyclic plasma oxidation and selective chemical oxide etching. The recess depth of 12.3 nm and low RMS roughness were measured by AFM and the Pt/AlGaN interface was examined by STEM. The gate recess resulted in a ~1 V positive threshold voltage shift and in the reduction of the drain current due to lower 2DEG density in the gate region, as compared to non-recessed sensors. After the gate recess the sensing response increased from 0.4 % to 2.1 % and from 13.2 % to 42.2 % for 5 ppm and 300 ppm H2 concentration, respectively. A comparison of transient characteristics revealed a 1.7x faster response and 2x faster recovery time of the recessed-gate Pt-HEMT sensor at 250 ppm H2 concentration as well as low hysteresis.