Numerical Simulation of Semiconductor Devices and Circuits for THz Applications

Electromagnetic waves with a frequency in the range from 0.1 to 10 THz are referred to as THz waves. They are difficult to generate, because their frequencies are on the one hand too high for efficient operation of state of the art solid-state devices and on the other too low for optical generators. Current generators extract the third harmonic of an oscillator, leading to extremely low power efficiency. This led to the proposal of a new kind of solid-state devices based on plasma waves in quasi 2D electron gases, where the THz signal is generated directly within the device. Since the dispersion relation of the plasma waves, their instabilities and the gain of the device depend on the structure, permittivity of the materials, dimensionality of the electron gas and its density, boundary conditions etc., it gives the device designer a lot of freedom and various device concepts have been proposed but yet not been realized. For accurate prediction of the device performance simulation engines employing an approach beyond the 1D transmission line models are required. The standard electron/hole transport models based on the Euler equation are to be generalized to describe transport in THz regimes, e.g. by a convective term or moments of higher order (e.g. hydrodynamic model). This requires novel numerical algorithms ranging from generalizations of the Scharfetter-Gummel stabilization, numerical integration techniques for THz oscillations, e.g. trigonometric spline-wavelet methods, to iterative linear and nonlinear solvers for huge systems of equations. The device behavior must be simulated within a circuit environment, since the signal power which can be decoupled depends on the termination of the device`s ports and each individual configuration has to be simulated since the circuit behavior is nonlinear. Thus, a coupled device/circuit simulator is required to investigate nonlinear effects.

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