Terahertz detection using germanium-based photoconductive antennas on various substrates

Germanium (Ge) is emerging as a promising material for terahertz (THz) devices due to its non-polar nature, which enables gapless, broadband radiation. It also offers the advantage of CMOS compatibility and can be adapted to various substrates. In this work, we demonstrate the compatibility of Ge films deposited by DC magnetron sputtering on high-resistive silicon and on low-cost insulating substrates, glass and Kapton, for the detection of free-space THz pulses. With the growing interest in the field of flexible electronics, it is essential to explore THz devices that can be integrated onto flexible platforms for which Kapton offers a clear advantage. We demonstrate THz detection using Ge-on-glass and Ge-on-Kapton photoconductive antennas (PCAs) with ZnTe as a THz emitter, achieving spectral bandwidths of 1.5 and 1.2 THz with signal-to-noise ratios (SNRs) of 27 and 23 dB, respectively. On the other hand, with a commercial GaAs as a PCA emitter, a Ge-on-Si PCA detected up to 2 THz with an SNR of 27 dB. We report on the compatibility of laser systems and the experimental constraints that depend on the choice of substrates.