Sub-bandgap excitation properties of LT-GaAs-based photoconductive antennas for terahertz pulse emission and detection
Photoconductive antennas (PCSs) with low-temperature grown GaAs (LT-GaAs) substrate are the most commonly used for terahertz (THz) pulsed emission and detection with femtosecond laser excitations. Their sub-bandgap excitation properties are attracting much attention since cost-effective femtosecond laser sources are available in the sub-bandgap wavelength region from 1 to 1.6 μm. In this report, a systematic investigation on the properties of LT-GaAs PCA with the sub-bandgap excitations is reported. The sub-band gap excitation efficiency at wavelengths close to the bandgap of GaAs (~ 1 μm) has been found much lower than that with wavelengths at around mid-bandgap excitations (1.5 ~ 1.6 μm). This counterintuitive observation is discussed in relation with the defect states distribution in LT-GaAs.