A unified photo-excited GaAs model from ab initio simulation in terahertz regime

Abstract

In this paper, we present a unified model for gallium arsenide (GaAs) based on ab initio simulations which characterizes its terahertz (THz) properties when excited by optical pump. We use density functional perturbation theory (DFPT) to calculate the dielectric properties of GaAs, and investigate the relaxation time of photo-excited GaAs through electron-phonon interactions (EPIs). In light of the complexities arising from the mixed absorption mechanisms and the sensitivity of GaAs to laser parameters, we have developed a method that leverages time-dependent density functional theory (TDDFT) and Boltzmann transport theory. This approach enables us to establish an accurate relationship between the pump laser intensity and the carrier concentration by introducing the percentage of excited electrons, facilitating the quantitative characterization of GaAs’s response under different optical pump intensities. Using the microscopic material parameters solved by first principles, we develop a unified Drude model to describe the macroscopic electromagnetic responses of photo-excited GaAs. We simulate several reported numerical examples of photo-excited GaAs, including a GaAs wafer and GaAs-based THz metamaterial modulators, to validate the proposed unified model as a reliable approach for predicting the THz properties of GaAs. The good agreement between the simulation and measurement results demonstrates that our model successfully captures the dynamic responses of photo-generated carriers and provides guidance for the design of optoelectronic devices based on GaAs. Furthermore, our modeling approach based on ab initio simulations is free from empirical parameters, providing a solid THz modeling method for other photo-excited semiconductor materials.

A spatiotemporal encoding metasurface design for manipulation of integrated radiation-scattering characteristic

“…has provided an unprecedented degree of freedom to dynamically control the electromagnetic wave [17]. By employing tunable components or materials, such as PIN diode [2], varactor [18], vanadium oxide (VO 2 ) [19], and gallium arsenide (GaAs) [20], etc., the resulting programmable metasurface can control the electromagnetic responses in real time. With the logically arranging the spatial coding sequences or performing time coding sequences, metasurface based functional devices demonstrate various promising applications in scattering wave control.…”