A hybrid time-domain model for pulsed terahertz dipole antennas (original) (raw)
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A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.
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Since the observation of radiation in the Terahertz (THz) frequency range from photoconductive antennas exited by femtosecond (fs) laser pulses, considerable efforts have been made to understand the mechanism responsible for THz generation, and to develop applications in THz Time-Domain Spectroscopy (THz-TDS). In this paper, the calculation of THz radiation from biased photoconductive antenna is reported, given some amelioration of the calculation model and classical Drude-Lorentz theory. Some simulation results based on the new calculation model are shown.
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The design process of a photoconductive antenna (PCA), which emits efficiently in the electromagnetic terahertz range, demands some considerations that are discussed through this work. In this work, several essential characteristics of a photoconductive antenna made with LT-GaAS are studied by means of well established commercial software (COMSOL 5.3 [1]). An approach to the efficiency is also made through the study of geometry, the laser illumination position, the substrate doping distribution, the direction of the bias applied to the semiconductor, the matching impedance at the laser operating frequency and, finally, the plasmonics effects or penetration laser enhancement due to the use of nano antennas. We study and compare two kinds of structures, one which is quasi-bidimensional or planar and the other which is vertical. Additionally, the photoconductive antennas are also modeled by using a simplified equivalent circuit which helps to understand the antennas' performance. Therefore some fundamental parameters, like the transient capacitance between the metal contacts are also studied. Furthermore, we introduce an optimized vertical design which achieves the best results.
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Journal of the Optical Society of America B, 2005
We investigate the antenna characteristics of a metal tip coupled to terahertz (THz) pulses generated from a photoconductive switch. Enhanced terahertz pulse emission is observed with the metal tip in contact with one of the electrodes of the photoconductive switch. Measurements of the angular dependence of the emitted THz radiation show that the metal tip acts as a highly directional antenna with radiation patterns well described by the theory for long-wire traveling-wave antennas. Similar behavior is observed for the metal tip acting as a THz pulse receiver, in accordance with the reciprocity principle. Effects related to the broadband nature of the THz pulses are discussed.
On the Numerical Modeling of Terahertz Photoconductive Antennas
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This paper shows the relevance of mobility models to describe the carrier dynamics for the analysis of radiative semiconductor photoconductive devices in the terahertz regime. We have built a simulator that self-consistently solves the device physics and Maxwell's equations to study the radiated fields. In particular, we show a significant influence of an accurate description of the steady-state regime of the semiconductor device for calculating radiated electromagnetic fields in the broadside direction. Comparison with measurements shows the accuracy of our simulator and demonstrates the superior performance of numerical schemes based not only on the description of the carrier, electric potential, and field distributions, but also on reliable local mobility models.