Response Enhancement of Pt–AlGaN/GaN HEMT Gas Sensors by Thin AlGaN Barrier with the Source-Connected Gate Configuration at High Temperature

Abstract

AlGaN/GaN HEMT hydrogen gas sensors were optimized by AlGaN barrier thickness in the gate-source connected configuration demonstrated high response and robust stability up to 500 °C. First, we found that the hydrogen sensing performance of a conventional normally-on HEMT-based sensor was enhanced when zero voltage was applied on the gate in comparison with a floating-gate condition due to a reduced level of the base current. In the next step, to take advantage of the response increase by VGS = 0 V, a new type of sensor with a source-connected gate (SCG) was fabricated to utilize the normally-on operation of the GaN HEMT sensor as a two-terminal device. AlGaN barrier thickness was thinned by the dry-etching process to gain higher transconductance at a zero-gate bias with the reduction of the distance from the 2DEG channel to the AlGaN surface, thereby significantly improve the hydrogen response. The SCG GaN sensor with an ultra-thin AlGaN barrier (9 nm) exhibited responses of 85% and 20% at 200 and 500 °C, respectively, onto 4%-hydrogen gas, which demonstrates a promising ability for harsh environment applications.

Recent progress on group III nitride nanostructure-based gas sensors

“…When the measurement was done on the as-fabricated sensor and 6 months later, no significant change in transfer characteristics was observed. 151 In another work, Vuong et al 152 reported the enhancement in the response of Pt-AlGaN/GaN HEMT hydrogen gas sensors by employing a thin AlGaN barrier with the source-connected gate configuration. The Pt-gate-based AlGaN/GaN HEMT gas sensors were processed on an Si substrate, where the arrangement of the structural layers contained a GaN buffer layer, followed by 23 nm thick AlGaN barrier layer, 4 nm-thick GaN capping layer, and finalized with a 10 nm in situ-deposited SiN x passivation layer.…”

“…25(a-f) demonstrate the important device characteristics of the gas sensor. 152 5. Group III nitride gas sensors with functionalized gate electrode Recently, metal, metal oxide, carbon nanotube, and graphene nanostructures have been extensively investigated for chemiresistive sensing applications.…”

Ten Years Progress of Electrical Detection of Heavy Metal Ions (HMIs) Using Various Field-Effect Transistor (FET) Nanosensors: A Review

“…To date, the AlGaN/GaN high electron mobility transistor (HEMT) devices have been intensively studied for ion and biomolecule sensing applications such as gas sensors, chemical sensors and biosensors [ 175 , 176 , 177 ]. A typical HEMT epitaxial sensor device structure consists of a substrate (usually Si or sapphire), GaN buffer layer, AlGaN barrier layer, and GaN cap layer.…”

“…( b ) Top view image of an AlGaN/GaN HEMT sensor with floating gate. Reproduced with permission from [ 175 ]. Copyright 2021 MDPI.…”

High Selectivity Hydrogen Gas Sensor Based on WO3/Pd-AlGaN/GaN HEMTs

“…In recent decades, semiconductor hydrogen gas sensors based on AlGaN/GaN ] developed rapidly because of their many advantages, such as physical and chemical stability, low cost in mass production, and ability to integrate into the circuit [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. GaN-based gas sensors especially demonstrated excellent capability for extreme environments such as high temperatures and high radiation [ 25 , 26 , 27 , 28 ]. Compared with the AlGaN/GaN diode type, the HEMT-type sensors exhibited several outstanding advantages, including lower theoretical detection limits, the separation of the current-carrying and the sensing mechanism, and the optimization of the sensor’s performance by gate bias modulation [ 29 ].…”