The physical mechanism of threshold voltage (V_TH) instability in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) was identified via capacitance-mode deep-level transient spectroscopy characterization. MIS-HEMTs with low-pressure chemical vapor deposited (LPCVD) SiN_x as the gate insulator feature two distinctive trap-emission transients. The initial transient corresponds to emission of states at the SiN_x/AlGaN interface, and the extracted density of state exhibits an exponential decay distribution. The subsequent transient is revealed due to hybrid emission of the interface and bulk states from the LPCVD-SiN_x gate insulator, which features an activation energy higher than 1.1 eV and a capture cross section that ranges between 1 × 10⁻¹¹ and 1 × 10⁻¹⁰ cm². The bulk states in the LPCVD-SiN_x gate insulator become charged under high gate voltage overdrive, leading to severe V_TH instability in GaN-based MIS-HEMTs.

The kink effect is a phenomenon that typically occurs in InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) at cryogenic temperatures. It results in higher output conductance (gDS) and non-monotonic behavior. This Letter discusses the origin and suppression of the kink effect in InP HEMTs at cryogenic temperatures, which is linked to the structure of gate recess passivation. At room temperature, two devices with different gate recess passivation structures show similar characteristics. However, a temperature-sensitive kink is observed in the non-passivated gate recess structure, leading to the discontinuous transconductance (gm) and the non-monotonic threshold voltage (Vth) shifts. Based on pulsed and static (non-pulsed) measurement data, surface traps and impact ionization in the high-field region are identified as the origin of the kink effect. Specifically, a positive Vth shift of +160 mV is caused by surface traps when the temperature drops to 150 K. A negative Vth shift of –60 mV is due to the enhanced impact ionization below 150 K. Conversely, the device with a passivated gate recess has a negligible kink effect and effectively improves discontinuous gm and the non-monotonic Vth shifts (+25 mV) when the temperature drops. Therefore, the device with a passivated gate recess is significant for suppressing the kink effect and maintaining the stability of the device in variable temperature environments.

Contact resistance ( R _C ) is of great importance for radio frequency (RF) applications of graphene, especially graphene field effect transistors (FETs) with short channel. FETs and transmission line model test structures based on chemical vapor deposition grown graphene are fabricated. The effects of employing traditional lithography solvent (Acetone) and strong solvents for photo resist, such as N, N-Dimethylacetamide (ZDMAC) and N-Methyl pyrrolidone (NMP), are systematically investigated. It was found that ZDMAC and NMP have more proficiency than acetone to remove the photo-resist residues and contaminations attached on graphene surface, enabling clean surface of graphene. However, strong solvents are found to destroy the lattice structure of graphene channel and induce defects in graphene lattice. Clean surface contributes to a significant reduction in the R _C between graphene channel and metal electrode, and the defects introduced on graphene surface underneath metal electrodes also contribute the reduction of R _C . But defects and deformation of lattice will increase the resistance in graphene channel and lead to the compromise of device performance. To address this problem, a mix wet-chemical approach employing both acetone and ZDMAC was developed in our study to realize a 19.07% reduction of R _C , without an unacceptable mass production of defects.

Cryogenic InP High-electron-mobility transistors (HEMTs)-based low-noise amplifiers (LNAs) have been applied in deep space exploration, which demands high performance from InP HEMTs. Specifically, at low temperatures, the device needs to achieve low power consumption and high operating frequency. In this study, we fabricated a double-recessed InP HEMT with a heavily doped In0.65Ga0.35As/In0.53Ga0.47As/In0.52Al0.48As multilayer cap structure to optimize the device’s performance at low temperatures. At low temperatures, excessive on-resistance (RON) leads to increased power dissipation and also contributes to higher noise, which affects the performance of the LNAs. We employed the heavily doped In0.65Ga0.35As layer to reduce the metal-semiconductor contact resistance, thereby effectively lowering RON. Experimental results show that at 7 K, the devices RON is 410 ٷlm, which could effectively reduce the power dissipation. Additionally, we adopted a double-recessed gate structure. This structure significantly improves the device’s maximum oscillation frequency(fmax) by reducing the parasitic capacitance. At 7 K, the device’s fmax reaches 740GHz. Furthermore, the design of the second gate recess reduces the exposed area of the gate recess, which combined with the Si3N4 passivation layer, effectively suppresses the kink effect caused by surface traps at low temperatures, further improving the device’s cryogenic performance.