Abstract

Using GaAs epilayers with arsenic precipitates (GaAs:As)[1] as the photoconductive material in a complete, broad-band optoelectronic teraHz beam system[2], we have generated and detected freely-propagating, subpsec electromagnetic pulses. Our results indicate that the photoconductive response of the GaAs:As consists of an ultrafast, subpsec turn on time followed by a turn off time of several picoseconds. Both the transmitter's and receiver's performances are dominated by the leading edge (turn on time), with the receiver working effectively in an "integrating mode." The ultrafast turn on is indistinguishable from that of epi-GaAs and indicates a GaAs matrix that is essentially free of point defects. The short "effective" carrier lifetime of several psec is consistent with capture by the embedded, closely-spaced (about 20 nm) arsenic precipitates. This behavior is contrasted with that of materials containing a uniform distribution of recombination centers, such as implanted silicon-on-sapphire or un-annealed, low-temperature GaAs.

© 1991 Optical Society of America