Germanium–Tin (GeSn) Terahertz Photoconductive Detector

Abstract

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We engineered the photocarrier dynamics of the complementary metal–oxide–semiconductor (CMOS)-compatible material germanium tin (GeSn) through controlled phosphorus ion implantation. The incorporation of Sn atoms into the Ge lattice reduces the bandgap, thereby red-shifting the absorption edge into the short-wave infrared (SWIR) region while concurrently enhancing carrier mobility. To overcome the inherently slow carrier recombination associated with the indirect bandgap nature of GeSn, phosphorus implantation was introduced to enable the ultrafast photoresponse in terahertz (THz) photoconductive antenna (PCA) detectors without substantially compromising electrical resistivity or carrier mobility. The ion-implanted detector achieves a broadened detection bandwidth of up to 2.5 THz, a signal-to-noise ratio (SNR) above 65 dB, and a 4-fold increase in response compared with the intrinsic GeSn device counterpart. These findings highlight GeSn as a promising group-IV material for ultrafast THz detection. They also demonstrate a CMOS-compatible THz photonic integrated circuit (PIC) pathway operating at telecommunication wavelengths.