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. @en

In this paper, a method to extend the detection range of hydrogen sulfide (H2S) gas sensor is demonstrated. The sensor is based on AlGaN/GaN high electron mobility transistors (HEMTs) with Pt gate. It is observed that the as-fabricated devices exhibited sensing signal saturation at 30 ppm H2S exposure in dry air. A pre-treatment using H2 pulses in dry air ambient at 250 °C was applied to extend the detection range of the sensor. The H2 treated H2S gas sensor was able to detect a higher H2S concentration up to 90 ppm at 250 °C without complete saturation.@en

A particulate matter micro-sensor for automotive exhaust systems based on a gateless wide-bandgap AlGaN/GaN high electron mobility transistor was developed and tested. Soot particles were generated by a laminar diesel flame and characterized with Raman spectroscopy, thermogravimetric analysis and scanning electron microscopy. Particle adsorption at the rate of 0.25 µg/min on the sensor surface resulted in 5.52% sensing response after 20 s and large signal variation of 4.44 mA, indicating fast response time. Saturated response of 34.72% (27.94 mA) was obtained after 10 min of deposition. The sensitivity towards soot is attributed to the modulation of the two-dimensional electron gas density by charged particles on the sensing surface. After soot deposition, the sensor was successfully regenerated by thermal oxidation of the carbonaceous particles at 600 °C. The sensing response remained unchanged post-regeneration indicating high temperature stability and harsh environment operation compatibility of the demonstrated GaN-based sensor. Nevertheless, interconnect metal optimization is still required to mitigate high-temperature interdiffusion.@en

Ohmic contacts to AlGaN/GaN with different metal stacks on Si or Sapphire substrate are fabricated and compared in this paper. For Au-capped ohmic contacts, the lowest contact resistances of 0.7 Ω·mm and 1.3 Ω·mm are achieved by Ti/Al/Ti/Au (20/110/40/50 nm) and Ti/Al/Ni/Au (20/110/40/50 nm) stacks, respectively. It also shows that the substrate material and epitaxial structure play an important role in ohmic contact engineering. For CMOS compatible Au-free structures, the Ti/Al/W (20/100/30 nm), Ti/Al/Ni/W (20/100/20/10 nm) and (20/100/10/20 nm) are demonstrated with the minimum contact resistance values of 0.45, 1.3, and 1.6 Ω·mm, respectively. The three metal stacks of Au-free ohmic contact are compared and obtained results are explained.@en

Ohmic contacts to AlGaN/GaN with different metal stacks on Si or Sapphire substrate are fabricated and compared in this paper. For Au-capped ohmic contacts, the lowest contact resistances of 0.7 Ω·mm and 1.3 Ω·mm are achieved by Ti/Al/Ti/Au (20/110/40/50 nm) and Ti/Al/Ni/Au (20/110/40/50 nm) stacks, respectively. It also shows that the substrate material and epitaxial structure play an important role in ohmic contact engineering. For CMOS compatible Au-free structures, the Ti/Al/W (20/100/30 nm), Ti/Al/Ni/W (20/100/20/10 nm) and (20/100/10/20 nm) are demonstrated with the minimum contact resistance values of 0.45, 1.3, and 1.6 Ω·mm, respectively. The three metal stacks of Au-free ohmic contact are compared and obtained results are explained.@en

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 (VTH) shifted from -1.57 to 1.49 V. A shallow recess (5 nm) resulted in a 1.03 mA increase in signal variation (AIDS), 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.@en