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Enhancement-mode transistors with uniform turn-on threshold voltage (V th ) can be achieved using low damage and low rate gate recess etching techniques. In this work, dry etching conditions for a AlGaN/GaN heterostructure with an ultra-low etching rate of 1.5 nm/min were demonstrated and we succeeded the possibility to achieve a low etch rate of an AlGaN/GaN heterostructure in a Cl 2 /BCl 3 plasma using inductively coupled plasma (ICP). The etching development was successfully implemented in the achievement of a normally-off GaN/AlGaN based transistor. The optimal recess depth was determined after fabrication of various devices with different recess depth values and with various dry etching conditions and after examining the performances of fabricated devices various conditions, and determining the dependence of recess time. The optimized etching condition resulted in low damage and smooth morphology of the etched AlGaN/GaN surfaces. Fine control of the depth of the gate region recess was achieved for the AlGaN/GaN heterostructure without any etch-stop layer, and validated for the fabrication of field effect transistors (FETs) using conventional processes. The fabricated normally-off Al 2 O 3 /AlGaN/GaN MOSFETs delivered a high positive V th of +5.64 V with a low off-state leakage current of ∼10 −7  A/mm and lower current collapse. [ABSTRACT FROM AUTHOR]

This experimental study focuses on the positive bias temperature instability (PBTI) in a fully recessed-gate AlGaN/GaN MOS-HEMT. A positive stress voltage to the gate results in positive threshold voltage shift (ΔV th ), which is attributed to the trapping of electrons from the GaN layer into the pre-existing oxide traps. The trapping rate exhibits a universal decreasing behavior as a function of the number of filled traps, independently of stress time, stress voltage, stress temperature, and device-to-device variability. The stress-induced ΔV th can be fully recovered by applying a small negative voltage, which causes the electron de-trapping. In the explored time window (between 1 s and thousands of s), the recovery dynamics is well described by the superimposition of two exponential functions associated with two different traps. Both trap time constants are independent of the stress voltage, decrease with temperature and increase with the recovery voltage. The activation energy of the slower trap is 0.93 eV, while the faster trap exhibits an activation energy with a large spread in the range between 0.45 eV and 0.82 eV. [ABSTRACT FROM AUTHOR]

A novel SOI MESFET with the modified depletion region using a Triple Recessed Gate (TRG-SOI MESFET) is presented for RF applications. The proposed gate consists of lower and upper gate to control the channel thickness and the depletion layer will change by omitting part of total charge due to locating gate in the channel. The key idea of this shaped gate is to modify the depletion region and the charge distribution of the channel in order to lower the electric field of the device and improving the breakdown voltage. In addition the maximum power density, the maximum oscillation frequency, the cutoff frequency, and the minimum noise figure for the proposed structure are improved due to increasing the drain-source resistance and the transconductance and decreasing the gate resistance. Therefore, the TRG-SOI MESFET can be used for high-power and high frequency applications. [ABSTRACT FROM AUTHOR]

This article critically reviews the materials, processing and reliability of InP high electron mobility transistors (InP HEMTs) for future terahertz wave applications. The factors such as drain current (I D) over 1200 mA/mm, transconductance (g m) over 3000 mS/mm, cut off frequency (f T) over 700 GHz and maximum oscillation frequency (f max) over 1300 GHz makes InP HEMTs suitable for Terahertz wave applications. Furthermore, low DC power consumption and outstanding low noise performance makes InP HEMT most appropriate transistor technology for the development of space based receivers. This review article critically assesses the challenges in miniaturization of InP HEMTs, doping strategies in InP HEMTs, buried platinum technology, impact of annealing process and temperature, influence of electron and proton irradiation, thermal and bias stress on the reliability of InP HEMTs, cavity and gating effects and influence of trapping effects. InP HEMTs are very much preferable in applications like radio astronomy, terahertz optical and wireless communication systems, atmospheric imaging and sensing, automotive radar, ground based receivers in deep space networks, terahertz imaging and sensing, biomedical applications, security screening, video conferencing & real time multimedia file transfer, high speed and ultra low power digital integrated circuits. [ABSTRACT FROM AUTHOR]