Low-temperature gallium arsenide substrate terahertz optical antenna: transient current and electromagnetic radiation simulation study

This paper constructs a two-dimensional optical antenna model. It simulates the process of generating transient current pulses and terahertz electromagnetic radiation pulses on a low- temperature gallium arsenide (LT-GaAs) substrate by applying a DC bias voltage and rapid pulse laser illumination, which excites the generation of electron-hole pairs. The study uses the semiconductor interface to calculate the transient current density and utilizes the electromagnetic wave, transient interface to simulate the generation and propagation of terahertz pulses. The simulation results show that the decay rate of the photocurrent is slower than the generation rate, which is due to the pulse duration being much shorter than the carrier lifetime; the terahertz pulse propagation animation reveals the propagation process of the pulse from the optical antenna and the effect of substrate reflection on the wavefront; the far-field spectrum indicates that the pulse reaches its strongest peak at about 0.75THz and the power extends to nearly 5THz; spectral analysis shows that due to the presence of the substrate, the far-field spectrum of the optical antenna in the y-direction and x-direction shows as light directivity difference. This study not only demonstrate to use COMSOL software to simulate optical antennas in the terahertz band but also provides a theoretical basis and technical support for the application of terahertz technology in security imaging, medical imaging, and communication fields. In addition, the establishment of this model provides possibilities for further optimizing the design of terahertz devices and improving their performance.