Field Screening in Low-Temperature-Grown GaAs Photoconductive Antennas

This paper investigates the nature of the signals obtained in double-pulse-excitation THz-emission experiments performed on terahertz antennas with low-temperature-grown GaAs as photoconductive material. Results of such measurements on devices containing photoconductive gaps with an area below 100 µm 2 have been interpreted in the past as evidence for screening effects by space charge build-up. We argue that this interpretation leads to discrepancies with what is known about charge-carrier dynamics. In analogy to the much-better-studied response of large-area emitters (photoconductors with an active area on the order of a square centimeter), we argue that radiation-field screening must be considered when interpreting the data of small-area emitters.