Radio Frequency InGaAs MOSFETs

Abstract: III-V-based Indium gallium arsenide is a promising channel material for high-frequency applications due to its superior electron mobility property. In this thesis, InGaAs/InP heterostructure radio frequency MOSFETs are designed, fabricated, and characterized. Various spacer technologies, from high dielectric spacers to air spacers, are implemented to reduce parasitic capacitances, and fT/fmax are evaluated. Three types of RF MOSFETs with different spacer technologies are fabricated in this work.InP ∧-ridge spacers are integrated on InGaAs Nanowire MOSFET in an attempt to decrease parasitic capacitances; however, due to a high-dielectric constant of the spacers and smaller transistors transconductance, the fT/fmax are limited to 75/100 GHz. InGaAs quantum well MOSFETs with a sacrificial amorphous silicon spacer are fabricated, and they have capacitances of a similar magnitude to other existing high-performing RF InGaAs FETs. An 80 nm InGaAs MOSFET has fT/fmax = 243/147 GHz is demonstrated, and further optimization of the channel and layout would improve the performance. Next, InGaAs MOSFETs with nitride spacer are fabricated in a top-down approach, where the heterostructure is designed to reduce contact resistance and thus improve transconductance. In the first attempt, from the electrical characterization, it is concluded that the ON resistance of these MOSFETs is comparable to state-of-the-art HEMTs. Complete non-quasi-static small-signal modeling is performed on these transistors, and the discrepancy in the magnitude of fmax is discussed. InGaAs/InP 3D-nanosheet/nanowire FETs' high-frequency performance is studied by combining intrinsic analytical and extrinsic numerical models to estimate fT/fmax. 3D vertical stacking results in smaller parasitic capacitances due to electric field perturbance because of screening.An 8-band k⋅p model is implemented to calculate the electronic parameters of strained InxGa1-xAs/InP heterostructure-based quantum wells and nanowires. Bandgap, conduction band energy levels, and their effective masses and non-parabolicity factors are studied for various indium compositions and channel dimensions. These calculated parameters are used to model the long channel quantum well InGaAs MOSFET at cryogenic temperatures, and the importance of band tails limiting the subthreshold slope is discussed.