Implant-free high-mobility flatband MOSFET: principles of operation

Principles of operation of implant-free enhancement-mode MOSFETs (flatband MOSFET) are discussed. Epitaxial-layer structures designed for use in implant-free enhancement-mode devices and employing a high-kappa dielectric (kappacong20) and a strained InGaAs channel layer with a thickness of 10 nm have been manufactured on GaAs substrate. Proceeding from measured electron mobility mu as a function of the sheet-carrier concentration, enhancement-mode design considerations, saturation current I_Dss, and mobility requirements are discussed using two-dimensional device simulations. For the flatband MOSFET to compete successfully with other device designs, certain minimum channel mobilities are required. For RF applications, mu should exceed 5000 cm²/Vs while high-performance MOSFETs for digital applications may require even higher mobility for optimum operation. Finally, measured data of first 1-mum-GaAs-flatband enhancement-mode MOSFETs are presented; the saturation velocity of the InGaAs channel layer is derived; and measured I_Dss data are compared to the results obtained by simulations