Effect of heteroepitaxial growth on LT-GaAs: ultrafast optical properties

Epitaxial low temperature grown GaAs (LT-GaAs) on silicon (LT-GaAs/Si) has the potential for terahertz (THz) photoconductive antenna applications. However, crystalline, optical and electrical properties of heteroepitaxial LT-GaAs/Si can be very different from those semi-insulating substrates (reference). In this study, we investigate an epitaxial sample, compared to a reference under same substrate temperature, with layer thickness. Anti-phase domains some crystal misorientation are present in LT-GaAs/Si. From coherent phonon spectroscopy, intrinsic carrier densities estimated ~$10^{15}$ cm$^{-3}$ either sample. Strong plasmon damping is also observed. Carrier dynamics, measured by time-resolved THz spectroscopy at high excitation fluence, reveals markedly responses between samples. Below saturation, both samples exhibit desired fast response. Under fluences $\geq$ 54 $\mu$ J/cm$^2$, LT-GaAs shows saturation electron trapping states leading non-exponential behavior, but maintains double exponential decay. The difference attributed formation As-As Ga-Ga bonds during growth LT-GaAs/Si, effectively much lower density As-related traps.