Search

The effect of ambient temperature on the detection sensitivity of carbon monoxide (CO) using ZnO nanorod-gated AlGaN/GaN high electron mobility transistor (HEMT) sensors was studied over a range of temperatures from 25 to 400 °C. An increase of the HEMT drain current was observed for exposure to the CO-containing ambients, due to chemisorbed oxygen on the ZnO surface reacting with CO to form CO2 and releasing electrons to the oxide surface, increasing the counter charges in the two-dimensional electron gas channel of the HEMT. By increasing the detection temperature from 25 °C to 150 °C, the CO detection sensitivity, ΔI/I, and detection limit were significantly improved from 0.23% to 7.5% and from 100 ppm to ∼30 ppm, respectively. However, the sensitivity of the CO detection was degraded by the decrease of mobility and saturation drain current of HEMT at temperatures higher than 200 °C. [ABSTRACT FROM AUTHOR]

The use of AlGaN/GaN high electron mobility transistor (HEMT) differential sensing diodes is shown to provide robust detection of 1% H2 in air at 25 °C. The active device in the differential pair is coated with 10 nm of Pt to enhance catalytic dissociation of molecular hydrogen, while the reference diode is coated with Ti/Au. The active diode in the pair shows an increase in forward current of several milliamperes at a bias voltage of 2.5 V when exposed to 1% H2 in air. The HEMT diodes show a response approximately twice that of GaN Schottky diodes, due to the presence of piezoelectric and spontaneous polarization in the heterostructure. The use of the differential pair removes false alarms due to ambient temperature variations. [ABSTRACT FROM AUTHOR]

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) functionalized with ZnO nanorods were used for sensing CO in the concentration range of 50–500ppm balanced with air at ambient and temperatures from 25 to 250°C. An increase of the HEMT drain current was observed for exposure to the CO-containing ambient. The sensing limitation was improved from 100ppm to 50ppm by increasing the sensor temperature from room temperature to 250°C. The sensing response was also enhanced from 0.09% to 0.34% by increasing the sensor temperature. Reliable and repeatable current changes with the introduction of a low CO concentration of 50ppm and also rapid response times of ∼40s and recovery times ∼15s were demonstrated. [Copyright &y& Elsevier]

Abstract: In this study, we report on a demonstration of hydrogen sensing at low temperature using SnO2 functionalized AlGaN/GaN high electron mobility transistors (HEMT). The SnO2 dispersion was synthesized via a hydrothermal method and selectively deposited on the gate region of a HEMT device through a photolithography process. The high electron sheet carrier concentration of nitride HEMTs provides an increased sensitivity relative to simple Schottky diodes fabricated on GaN layers. The morphology and crystalline properties of the SnO2-gate, together with the texture of the multilayer films on the device were investigated by SEM, HRTEM, EDS and XRD. The effects of annealing treatment on the crystalline properties of the SnO2-gate, and gas sensing properties of SnO2-gated HEMT sensors were studied. The SnO2-gated HEMT sensor showed fast and reversible hydrogen gas sensing response at low temperature. [Copyright &y& Elsevier]

Abstract: The effect of bias voltage polarity on the hydrogen sensing characteristics of AlGaN/GaN heterostructure Schottky diodes is reported. Under forward bias, there was a maximum observed in the sensitivity for hydrogen detection. For reverse bias, the hydrogen detection sensitivity increased proportionally to the bias voltage. A detection limit of 10ppm of H2 in N2 was achieved under reverse bias with a current increase of 14% as compared to a detection limit of 100ppm of H2 for a similar current change under forward bias. [Copyright &y& Elsevier]