Fiber-coupled terahertz time-domain spectrometer with 10 THz bandwidth using InGaAs photoconductive membranes on silicon

We present a fiber-coupled terahertz (THz) time-domain spectrometer with a record bandwidth of 10 THz. This significant increase of 3.5 THz in bandwidth compared to state-of-the-art spectrometers is enabled by improved photoconductive antennas (PCAs). In particular, we show that THz absorption in the polar InP:Fe substrate of the standard InGaAs PCAs is the main limiting factor for the bandwidth. To overcome this issue, we have developed a wafer-scale substrate transfer-process for the thin photoconductive InGaAs layer from InP:Fe to low loss, high resistivity float-zone (HRFZ) silicon. The resulting photoconductive membrane (PCM) antennas combine the advantages of ultrafast iron-doped InGaAs photoconductors as efficient THz emitters and receivers with nearly absorption-free and spectrally flat transmission of HRFZ-Si up to 17 THz.