Study of Charge Carrier Transport in GaN Sensors
Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.
AlGaN/GaN heterostructure pH sensor with multi-sensing segments
Abstract pH sensor is very important in various fields, and has triggered many types of devices based on different materials and mechanisms. How to improve the performances of the sensors is one of major challenges now. In the present paper, we developed an idea to improve the sensitivity of pH sensors based on AlGaN/GaN high-electron-mobility transistors (HEMTs) by introducing multi-sensing segments, and experimentally fabricated prototype devicesand then investigated their responses to aqueous solutions under different pH values. The optimized sensor exhibits a very high linear sensitivity of 1.35 mA/pH at drain-source voltage of 1.5 V, which is much higher than those of conventional pH sensors with single open gate sensing area. This indicates that the multi-sensing segments is very effective in increasing the sensitivity of the pH sensor, rather than simply increasing the sensing area. The sensors degrade after measurement in solution for a long working time, but they can recover to their initial states in a certain duration after washing, typically ∼24 h. Our finding paves new strategy for the future design of high sensitive and stable pH sensors based on HEMTs.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.