Reduction of phonon resonant terahertz wave absorption in photoconductive switches using epitaxial layer transfer

A broadband terahertz time-domain spectroscopy (TDS) system for frequencies of up to 15 THz, including the phonon resonance frequency range, has been developed using a transferred thin-film photoconductive switch (PCS) detector. The thin-film PCSs, based on low-temperature-grown GaAs, were fabricated using epitaxial layer transfer onto high-resistivity Si substrates. We observed a reduction of phonon resonant absorption, including between 7 and 10 THz, in a forward radiation configuration. Numerically calculated absorption spectra show good agreement with our experimental results. This technique will provide compact, broadband TDS systems.