GaN Based Ethanol Sensor

Abstract

Ethanol is one of most common aliphatic alcohol, which is used in chemical, biomedical, and food industry including alcoholic beverage. In recent, there are growing demands for the ethanol gas sensor to detect early spoilage of carbohydrate food, and this kind of sensors are to be employed in consumer electronics including refrigerators and mobile devices. Electrochemical, optical, potentiometric, polymer, and semiconductor sensors have been developed for fast and accurate detection of ethanol. Among the various detection methods, semiconductor based sensor can be operated at low power consumption in compact size. So far now, metal oxide semiconductors such as SnO2, Fe2O3, CuO, and ZnO are researched mostly.GaN based material is very suitable for gas sensors, and has many superior material properties to oxide semiconductors. Wide bandgap of GaN enable devices to be operated at high temperature and harsh radiative environment, and mechanical and chemical robustness of GaN ensures reliability and durability of the device. Many types of GaN based gas sensing devices including Schottky diodes, metal oxide semiconductor (MOS) diodes, GaN nanowires and AlGaN/GaN high electron mobility transistors (HEMTs) which employ specific sensing material as a catalytic active layer have been developed for prompt and sensitive detection of target gas. Specially, AlGaN/GaN HEMT structure with 2 dimensional electron gas (2-DEG) channel induced by piezoelectric and spontaneous polarization at the interface between the AlGaN and GaN layers shows highly sensitive current changes to surface charges created by catalytic reaction of target gas on the specific active sensing layer. Typically, field effect transistors with higher drain current exhibit better responsivity of gas detection. With 30 % Al concentration in AlGaN layer, 5~10 times higher channel sheet electron densities are obtained compared to GaAs or InP HEMTs.In this study, AlGaN/GaN HEMT based Schottky diode ethanol sensor using silver as a sensing material was fabricated, and the response of the device to ethanol gas was investigated. The diode showed current reduction in ethanol ambient due to the increase of Shottky barrier height at 250oC, and fast reliable repeatability to cyclic exposures of various concentrations of ethanol gas.