Application of AlGaN/GaN Heterostructures for Ultra-Low Power Nitrogen Dioxide Sensing

Abstract

Ultra-low power room temperature NO 2 sensors are demonstrated using AlGaN/GaN. The chemically stable semiconductor was sensitized to increase the sensitivity to enable ultra-low power, low ppb level detection without additional heaters. Sensors were sensitized by two methods, ultra-thin ALD SnO 2 and surface enhancement by ICP-RIE in BCl 3 gas. Both sensitization techniques demonstrate room temperature response, while the unsensitized sensors did not respond. At room temperature, surface enhanced sensors show a significant increase in sensitivity compared to SnO 2 sensitized sensors. The Environmental Protection Agency has identified Nitrogen Oxides (NO x ) as one of 6 major air pollutants for health concern.1 This means people with existing respiratory conditions may have severe reactions requiring hospitalization. Even more concerning is the variability in concentrations of these pollutants. NO x varies quite heavily outdoors due to combustion sources, such as near highways and high traffic cities.2,3 These effects create the need for wearable, low power, continuous environmental monitoring systems for correlating health effects. Current state of the art NO 2 sensors are not suited for wearable platforms due to high power, slow response, and maintenance constraints.4 Gallium Nitride (GaN) has been identified as a promising sensing material due to its chemically stable surface.5 AlGaN/GaN heterojunctions have been shown to have good sensitivity to H 2 gas due to the exploitation of surface state defects that allow for modulation of the high mobility 2-Dimensional Election Gas (2DEG), but generally require sensor heating to obtain high sensitivity. [5][6][7] In this paper, AlGaN/GaN heterostructures were studied to evaluate low power NO 2 sensors will be explored and optimized to obtain ultra-low power, low noise, room temperature (RT = 20• C) sensing response by surface sensitization. ExperimentalAlGaN/GaN substrates were first patterned for device to device isolation using conventional photolithography and dry ICP-RIE etching in BCl 3 gas. Following isolation, interdigitated electrodes were defined using photolithography and lift off with a metal stack Ti/Al/Ni/Ti/Au (20 nm/100 nm/20 nm/5 nm/100 nm). The sensors received a rapid thermal anneal at 850• C for 30s in Nitrogen environment to obtain Ohmic contact to the 2DEG. Finally, the surface was sensitized by two approaches. The first approach utilizes ultra-thin SnO 2 (7 nm) by Atomic Layer Deposition (ALD) at 200• C, whereas the second approach is enhancement of adsorption sites at the surface of the GaN layer by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) in BCl 3 . The optical image and cross-sectional schematic of interdigitated electrodes are shown in Fig. 1.Sensor testing was performed in a custom-built stainless steel chamber equipped with a borosilicate chuck for high temperature testing, as well as ultra-violet (UV) LEDs for sensor recovery. Using the NIST-certified Teledyne T700U gas calibrator, NO 2 concentrations of 50-500 ppb were ...

Recent Advances in Electrochemical Sensors for Detecting Toxic Gases: NO2, SO2 and H2S

“…The fabricated heterostructure sensor exhibited robustness under severe environmental conditions with a very quick response time of 1 s. When sensors are integrated in chips, low power sensor operation is required. Lim et al [ 96 ] made SnO 2 sensitized AlGaN/GaN sensor operating at ultra-low power without using any heater. The fabricated sensor exhibited ppb level detection as well as fast response times.…”

Adsorption performance of M-doped (M = Ti and Cr) gallium nitride nanosheets towards SO2 and NO2: a DFT-D calculation

“…36 There are some experimental studies focusing on the GaN based NO 2 and SO 2 sensors. [37][38][39][40] Bishop et al 41 suggested a double Schottky junction NO 2 gas sensor based on BGaN/GaN. Triet et al synthesized Al 0.27 Ga 0.73 N/GaN-based Schottky diode sensors for SO 2 gas detection.…”

Boronate probe-based hydrogen peroxide detection with AlGaN/GaN HEMT sensor

“…The detected signal in the gate region is amplified and measured as a change in the 2DEG conductivity, which makes the HEMT a good sensing device. Based on this principle, HEMT sensors have demonstrated promising results in the detection of pH changes, 18 , 19 gas molecules, 20–22 DNA, 23 , 24 and cancer-associated antigens, 25 , 26 as well as in monitoring living cells. 27 , 28 Due to their unique electrical and chemical properties, the AlGaN/GaN HEMTs show great potential for the detection of reactive and transient biological components, such as reactive oxygen species (ROS).…”