Deterministic simulation of electron transport in III-V devices
III-V materials have a higher saturated electron velocity and higher electron mobility than silicon, so the transistors based on these materials are at the heart of many high frequency electronic devices used for high speed communication, near field radar (e.g. adaptive cruise control), security applications (e.g. millimeter wave imaging) or spectral analysis (e.g. gas detection).
Due to continued scaling of devices, the drift diffusion models can no longer describe them accurately. Instead, physically more sophisticated simulation approaches based on the Boltzmann transport equation (BTE) are desirable.
The usual approach to solve the BTE is the Monte Carlo method. This method has own disadvantages which arise from its stochastic nature. New deterministic methods have recently been developed to solve the BTE without stochastic errors.
An expansion of the k-space in Fourier harmonics is one of these non-stochastic methods. It has already been successfully applied to silicon devices.
For III-V materials, however, we need more elaborate expansions of Fourier harmonics. In silicon devices, the most important scattering like acoustic and inter-valley scattering are nonpolar and isotropic. For III-V materials, the most important scattering is polar optical phonon scattering. In contrast to isotropic processes, this type of scattering does not act randomizing on carrier velocity directions. It depends on the angle between the initial and final wave vector and this property affects the numerical stability of the BTE solution.
Small signal and noise analysis are important methods to evaluate the RF performance of devices. Compared to the stochastic Monte Carlo approach, a deterministic Fourier harmonics expansion solver can be implemented directly in the full frequency range including zero frequency, low current levels and slow processes without difficulties.
At the end of this project, we will have a comprehensive simulator for III-V semiconductor devices for DC, AC and noise analysis, which will cover all the involved time scales from femto- (electron scattering), over pico- (phonon scattering ) to milliseconds (slow traps).
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