Ultrafast photoconductors have been an enabling device technology in the THz field during the past decade. And their
implementation is now worldwide in time- and frequency-domains systems of various types. While the technological
push is towards InGaAs or similar photoconductors operating at 1550 nm, the GaAs-based devices operating around 800
nm still provide superior performance and robustness in most cases. This paper contrasts the GaAs and 1550-nm devices
in terms of materials design and solid-state metrics such as electron-hole lifetime, carrier mobility, and resistivity. It also
summarizes the main materials developed over the past 20 years.