Three-dimensional carrier-dynamics simulation of terahertz emission from photoconductive switches

TL;DR

This paper presents a semi-classical Monte Carlo simulation of three-dimensional carrier dynamics in GaAs-based photoconductive switches, analyzing THz emission power and bandwidth as functions of various parameters, revealing power limiting mechanisms and optimizing emission conditions.

Contribution

The study introduces a detailed 3D Monte Carlo model for carrier dynamics in photoconductive switches and identifies key factors affecting THz emission power and efficiency.

Findings

THz power is limited by pulse duration and screening effects.

Proximity of laser pulse to the anode enhances THz power.

Electric field distribution and carrier mobilities influence emission efficiency.

Abstract

A semi-classical Monte Carlo model for studying three-dimensional carrier dynamics in photoconductive switches is presented. The model was used to simulate the process of photoexcitation in GaAs-based photoconductive antennas illuminated with pulses typical of mode-locked Ti:Sapphire lasers. We analyzed the power and frequency bandwidth of THz radiation emitted from these devices as a function of bias voltage, pump pulse duration and pump pulse location. We show that the mechanisms limiting the THz power emitted from photoconductive switches fall into two regimes: when illuminated with short duration (<40 fs) laser pulses the energy distribution of the Gaussian pulses constrains the emitted power, while for long (>40 fs) pulses, screening is the primary power-limiting mechanism. A discussion of the dynamics of bias field screening in the gap region is presented. The emitted terahertz power was found to be enhanced when the exciting laser pulse was in close proximity to the anode of the photoconductive emitter, in agreement with experimental results. We show that this enhancement arises from the electric field distribution within the emitter combined with a difference in the mobilities of electrons and holes.