Rhodium-Doped Quantum Photoconductor with High Carrier Mobility > 3300 cm2/Vs and Eightfold Resistivity Enhancement via Co-Doping with Ruthenium

Photoconductive antennas (PCAs) for terahertz (THz) time-domain spectroscopy (TDS) require high carrier mobility and ultrashort carrier lifetime, a contradiction that represents a fundamental limitation. Quantum photoconductive antennas (QPCAs) aim to overcome this limitation by spatially separating carrier transport and trapping. However, their use has been limited to THz receivers only due to the low resistivity of their undoped, high-mobility InGaAs layers. Here, we present for the first time Rh-doped quantum photoconductors co-doped with Ru, with up to eight times higher resistivity. Ru acts as a highly electrically active deep-level acceptor, facilitating carrier compensation at low doping concentrations. In this way, a sixfold reduction in free electron concentration down to 1.4 × 1012 cm-3 is achieved, providing a very high resistivity of 1309 Ωcm, while maintaining an excellent carrier mobility of 3330 cm2/Vs. In addition, optical pump-probe measurements show a negligible effect of Ru-doping on the carrier lifetime, demonstrating that the QPCA principle of distinct charge carrier transport and trapping is maintained. These results represent an important milestone toward applying QPCAs as THz emitters in THz TDS.