J. Lloyd-Hughes

We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both experimentally and using a three-dimensional carrier dynamics simulation. A uniform density of vacancies was formed over the optical absorption depth of bulk GaAs samples by performing multi-energy implantations of arsenic ions (1 and 2.4MeV) and subsequent thermal annealing. In a series of THz emission experiments the frequency of peak THz power was found to increase significantly from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to 10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast carrier dynamics to reproduce and explain these results. The effect of the ion-induced damage was included in the simulation by considering carrier scattering at neutral and charged impurities, as well as carrier trapping at defect sites. Higher vacancy concentrations and shorter carrier trapping times both contributed to shorter simulated THz pulses, the latter being more important over experimentally realistic parameter ranges.

We simulate the terahertz emission from laterally-biased InGaAs and InP using a three-dimensional carrier dynamics model in order to optimise the semiconductor material. Incident pump-pulse parameters of current Ti:Sapphire and Er:fibre lasers are chosen, and the simulation models the semiconductor's bandstructure using parabolic Gamma, L and X valleys, and heavy holes. The emitted terahertz radiation is propagated within the semiconductor and into free space using a model based on the Drude-Lorentz dielectric function. As the InGaAs alloy approaches InAs an increase in the emitted power is observed, and this is attributed to a greater electron mobility. Additionally, low-temperature grown and ion-implanted InGaAs are modelled using a finite carrier trapping time. At sub-picosecond trapping times the terahertz bandwidth is found to increase significantly at the cost of a reduced emission power.