The AlInN/GaN high-electron-mobility-transistor (HEMT) indicates better performances compared with the traditional AlGaN/GaN HEMTs. The present work investigated the pH sensor functionality of an analogous HEMT AlInN/GaN device with an open gate. It was shown that the Al0.83In0.17N/GaN device demonstrates excellent pH sense functionality in aqueous solutions, exhibiting higher sensitivity (−30.83 μA/pH for AlInN/GaN and −4.6 μA/pH for AlGaN/GaN) and a faster response time, lower degradation and good stability with respect to the AlGaN/GaN device, which is attributed to higher two-dimensional electron gas (2DEG) density and a thinner barrier layer in Al0.83In0.17N/GaN owning to lattice matching. On the other hand, the open gate geometry was found to affect the pH sensitivity obviously. Properly increasing the width and shortening the length of the open gate area could enhance the sensitivity. However, when the open gate width is too larger or too small, the pH sensitivity would be suppressed conversely. Designing an optimal ratio of the width to the length is important for achieving high sensitivity. This work suggests that the AlInN/GaN-based 2DEG carrier modulated devices would be good candidates for high-performance pH sensors and other related applications.
AlGaN/GaN metal-insulator-semiconductor field-effect transistors with fin structures (AlGaN/GaN MIS-FinFETs) were fabricated and characterized by changing fin width and using different dielectric layers. The FinFET with 20 nm-thick SiO2 dielectric layer exhibits a very small subthreshold swing (SS) of 56 mV/decade. However, the threshold voltage of the device is too low to ensure low off-state leakage current (at the gate voltage of 0 V), even though the fin width of the device is reduced to 30 nm, which would not meet the requirement for low standby power consumption. On the other hand, the FinFET with a 10 nm-thick Al2O3 dielectric layer and a much wider fin width of 100 nm shows normally-off operation with a threshold voltage of 0.8 V, SS of 63 mV/dec, and very low off-state current of 1 nA/mm. When the fin width is reduced to 40 nm, the threshold voltage of the FinFET is increased to 2.3 V and the SS is decreased to 52 mV/decade. These excellent switching performances convince us that the FinFETs might be promising either for low voltage logic or for efficient power switching applications. The observed SS values, which are smaller than the theoretical Boltzmann limit (60 mV/decade), can be explained by the concept of the voltage-dependent effective channel width.
The effects of interface charges on the performances of gate-all-around (GAA) GaN vertical nanowire MOSFETs with different geometries have been studied. Geometrical effect on the gate current of vertical GAA GaN nanowire MOSFET has also been analysed for the first time. In the ideal condition, the circular geometry nanowire (CGN) MOSFET exhibits the best performance with subthreshold swing (SS) of 62 mV/dec, drain-induced barrier lowering (DIBL) of 14 mV/V, and ON/OFF current ratio (I ON /I OFF ) of ∼10 8 . The triangular or hexagonal geometry nanowire (TGN or HGN) MOSFET suffer from large gate leakage current due to the field enhancement at sidewall corners. It is also known that interface traps at the sidewall surface of vertical nanowires deteriorate the overall device performance. The HGN MOSFET with m-plane sidewall demonstrates the best performance with SS of 69 mV/dec and DIBL of 13 mV/V, while the TGN MOSFET with a-plane sidewall exhibits the worst performance with SS of 112 mV/dec and DIBL of 101 mV/V.
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