2D hydrodynamic simulation of TeraFETs beyond the gradual-channel approximation for transient, large-signal or ultrahigh-frequency simulations

Abstract

In the past decade, detection of THz radiation by plasma-wave-assisted frequency mixing in antenna-coupled field-effect transistors (TeraFETs) -- implemented in various semiconductor material systems (Si CMOS, GaN/AlGaN, GaAs/AlGaAs, graphene, etc.) -- has matured and led to a practically applied detector technology. This has been supported by the development of powerful device simulation tools which take into account relevant collective carrier dynamics and mixing processes in various approximations. These tools mostly model carrier transport in 1D and they are usually geared towards continuous-wave illumination of the device and small-signal response. Depending on their implementation, it may not be possible readily to simulate large-signal and pulsed operation. Another approximation which may lead to unsatisfactory results is the 1D restriction to calculate only the longitudinal electric field components. Especially at the edges of the gate electrode, solving of the 2D Poisson equation promises better results. This contribution introduces a stable way to solve the 2D Poisson equation self-consistently with the hydrodynamic transport equations including the numerically challenging convection term. We employ a well-balanced approximate Harten-Lax-van-Leer-Contact Riemann solver. The approach is well suited for a future treatment of transient and large-signal cases. The 2D treatment also generically extends the model beyond the gradual-channel approximation and allows to calculate the FET's response at high THz frequencies where the gate-to-channel potential acquires a non-local character. Model calculations are performed for the exemplary case of a 65-nm Si CMOS TeraFET in the isothermal approximation.