Terahertz emission and detection using Ge-on-Si photoconductive antennas

Germanium-on-silicon (Ge-on-Si) is a promising, CMOS-compatible platform for integrated terahertz (THz) photonics, offering a low-cost alternative to III-V semiconductors. A primary challenge for Ge-based photoconductive antennas (PCAs), however, has been the long carrier lifetime of bulk Ge, preventing its use as a detector. Here, we demonstrate that amorphous Ge (a-Ge) films overcome this limitation, possessing an inherent ultrashort carrier lifetime of ∼1.11–1.38 ps. We leverage this property to demonstrate coherent THz pulse detection using undoped a-Ge-on-Si PCAs. A comparative study of devices fabricated on a-Ge films grown by plasma-enhanced chemical vapor deposition (PECVD) and DC magnetron sputtering is presented. The PECVD-Ge device, with better homogeneity and a smoother morphology in the films, demonstrates superior performance for both THz emission and detection. As an emitter, the PECVD-Ge PCA achieves a 40 dB signal-to-noise ratio (SNR) with a bandwidth of ∼3 THz. As a detector, it achieves a 32 dB SNR and an ∼2 THz bandwidth, representing an ∼2.5-fold increase in detected signal amplitude over the sputtered-Ge device. These results establish amorphous Ge-on-Si as a viable and scalable platform for both THz generation and detection, paving the way for fully integrated Si-based THz time-domain systems.