Physics-Based Analytical Channel Charge Model of In_xGa_1-xAs/In_0.52Al_0.48As Quantum-Well Field-Effect Transistors From Subthreshold to Strong Inversion Regimes

This paper presents a physics-based analytical channel charge model for indium-rich InxGa1-xAs/In0.52Al0.48As quantum-well (QW) field-effect transistors (FETs) that is applicable from the subthreshold to strong inversion regimes. The model requires only seven physical/geometrical parameters, along with three transition coefficients. In the subthreshold regime, the conduction bands (EC) of all regions are flat with finite and symmetrical QW configurations. Since the Fermi-level (EF) is located far below EC , the two-dimensional electron-gas density (n2-DEG) should be minimal and can thus be approximated from Maxwell-Boltzmann statistics. In contrast, the applied gate bias lowers the EC of all structures in the inversion regime, yielding band-bending of an In0.52Al0.48As insulator and InxGa1-xAs QW channel. The dependency of the energy separation between EF and EC on the surface of the InxGa1-xAs QW channel upon VGS enables construction of the charge-voltage behaviors of InxGa1-xAs/In0.52Al0.48As QW FETs. To develop a unified, continuous and differentiable areal channel charge density (Qch) model that is valid from the subthreshold to strong inversion regimes, the previously proposed inversion-layer transition function is further revised with three transition coefficients of η, α and β in this work. To verify the proposed approach, the results of the proposed model are compared with those of not only the numerically calculated Qch from a one-dimensional (1D) Poisson-Schrödinger solver, but also the measured gate capacitance of a fabricated In0.7Ga0.3As QW metal-insulator-semiconductor FET with large gate length, yielding excellent agreement between the simulated and measured results.