We have successfully grown AlGaN/GaN high electron mobility transistor (HEMT) structure on the high-quality undoped thick AlN buffer layer with large band offset to replace the conventional high-resistivity GaN buffer layer. The AlGaN/GaN HEMT fabricated on this AlN buffer layer exhibits low OFF-state leakage current with high I _{\scriptscriptstyle ON} /I _{\scriptscriptstyle OFF} of ~ 10 ⁶ due to enhanced confinement of the electrons in the 2-D electron gas (2-DEG) channel. The undoped AlN buffer layer is responsible for suppressing the trapping effects to greatly reduce the current dispersion in pulsed I _{\text D} - V _{\text D} characteristics, which is hardly avoided in conventional deep acceptor-doped GaN buffer layer. The device also demonstrates high breakdown voltage of 2154 V with very high figure of merit (FOM) of ~1.8 GV $^{2-1}$ cm $^{-{2}}$ , one of the highest ever reported, suggesting that the AlGaN/GaN-based Hemts WITH AlN buffer layer are promising for high-performance RF and power applications.

AlGaN/GaN-based fin-shaped field-effect transistors with very steep side-wall have been fabricated by utilizing electron-beam lithography and subsequent anisotropic side-wall wet etch in tetramethyl ammonium hydroxide solution. The investigate device demonstrated extremely broad transconductance (g _m ) ranging from ~0 to ~8 V at V _D = 10 V, which is essential for high linearity device performance. Pulse measurement showed that the device exhibits negligible gate lag, but still suffers from drain lag. The device with L _GD of 17 μm exhibited excellent OFF-state characteristic with subthreshold swing of ~58 mV/decade, low OFF-state leakage current of ~10 ^-12 A, and breakdown voltage of ~400 V at V _G = -9 V.

In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT)-based biosensor for the detection of C-reactive protein (CRP) using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region.

In this paper, we investigated characteristics of AlGaN/GaN high-electron mobility transistors (HEMTs) with high resistive buffer structure consisted of periodically carbon-doped (PCD) GaN buffer layer and AlGaN back barrier layer. The PCD structure was proposed for reducing undesirable trapping effects, which resulted in effective suppression of the current collapse compared to that in conventional carbon buffer structure. To further improve the dynamic performances of the device and to increase the electron confinement of the 2-D electron gas (2-DEG) channel, AlGaN back barrier was inserted between the GaN channel and the PCD buffer layer, which results in greatly improved current collapse with slightly improved 2-DEG mobility compared to those of the device without back barrier. The OFF-state leakage current of the device with back-barrier is about 2 orders lower in magnitude than that of device without back barrier, which leads to the breakdown voltage of 2 kV and figure of merit of 2.27 GV ² Ω ^-1 cm ^-2 for the device with LGD of 10 μm, one of the highest values ever reported for the GaN-based HEMTs.