The electrical characteristics of a series of AlInN high-electron-mobility transistors (HEMTs) with a GaN cap layer ranging from 0 to 26 nm are investigated for power switching applications. The breakdown voltage (VB), mobility of two-dimensional electron gas, on-state resistance (Ron), and dynamic Ron of the HEMTs are improved by increasing the cap layer thickness. The improved electrical characteristics are attributed to the GaN cap layer, which not only reduces the surface E-field but also raises the conduction band of the barrier layer and effectively prevents electrons from being trapped in the AlInN barrier and above.
Pt/GaN Schottky diodes were fabricated for detecting hydrogen sulfide at 200 • C. Ga-face GaN was grown on c-plane sapphire substrate by a metal-organic chemical vapor deposition (MOCVD) system. Hydrogen sulfide was mixed with nitrogen and detected from 0.1∼10 ppm with the Pt/GaN Schottky diodes. Hydrogen sulfide caused the current increase in both forward and reversed bias of the Schottky diode. Real-time detection of the hydrogen sulfide was conducted at a forward bias 1.18 V in nitrogen ambient. The sensors show good linear dependence of the current change at forward bias versus the H 2 S gas concentration. The sensitivity in the two ranges from 0.1∼1 ppm and 1∼10 ppm of hydrogen sulfide, are 14.62 and 5.844 μA/ppm, respectively. The detection limit of the sensor is around 0. Hydrogen sulfide is a colorless and highly toxic gas, which is usually found in petroleum drilling, coal mining, or chemical industry. Hydrogen sulfide may cause severe damage to human body when people are exposed in more than 20 ppm. Early detection of hydrogen sulfide can protect people in workplace effectively. Hydrogen sulfide is also resulted from the bacterial degradation of protein, such as from seafood or meat. The concentration of hydrogen sulfide resulted from spoilage food is quite low. Therefore, microsensors for trace hydrogen sulfide detection are attractive for environmental monitoring in workplace and for inspection of the freshness of food as well. Conductive metal oxides, including ZnO, 1 CuO, 2 WO 3 , 3 SnO 2 , 4 and MoO 3 5 were investigated for hydrogen sulfide detection. Tungsten oxide with metal catalysts including Au, Pt and Ag, have showed response of hydrogen sulfide from 2∼30 ppm.6 Polythiophene/WO 3 hybrid structure showed hydrogen sulfide response as low as 5 ppm.
7Molybdenum oxide decorated with reduced graphene oxide showed 50 ppm hydrogen sulfide response.5 Pt/SiO 2 /Si MOS capacitor was also reported to detect more than 250 ppm hydrogen sulfide. 8 However, most of the solid-state microsensors can only detect hydrogen sulfide above 1∼10 ppm. On the other hand, GaN and AlGaN are attractive materials for the fabrication of various chemical and biochemical sensors. A number of sensors based on GaN or AlGaN/GaN Schottky diodes have been investigated as gas sensors. Many of them have been studied for hydrogen detection.9-11 Apart from the hydrogen detection, the Schottky diodes were also reported for detecting propane, 12 carbon monoxide, 13 acetylene (C 2 H 2 ), nitrous oxide (NO 2 ) 9 and ammonia (NH 3 ), 14 due to the good stability of GaN in high temperature and the high sensitivity of the GaN Schottky diodes. In this study, Pt/GaN Schottky is investigated for trace hydrogen sulfide detection in air as low as 0.1 ppm. The detection ranges from 0.1∼10 ppm of hydrogen sulfide. The results show that GaN Schottky diodes are suitable for portable devices, which can be used for instant and real-time hydrogen sulfide detection.
ExperimentalThe GaN layer was grown on c-plane sapphire substrate by a metalorganic che...
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