Abstract

Freely propagating, subpicosecond electromagnetic pulses with a bandwidth extending well into the far-infrared can be generated and detected using photoconducting switches. Several applications in spectroscopy have already been reported. However, all systems used have suffered from bandwidth limitations imposed by the receiver. The most common receiver substrate material is silicon-on-sapphire. One bandwidth limiting factor then arises from absorption of the high frequency components of the pulse in the sapphire.¹ In this work we demonstrate that GaAs-on-silicon is an attractive, alternative detector substrate material. A 1.5 μm layer of GaAs was grown at 460°C by MBE on a high-resistivity silicon wafer. High-resistivity silicon has negligible absorption and overcome. X-ray diffraction measurements indicate the formation of micro crystallites in the GaAs layer due to the lattice mismatch between GaAs and silicon. These material characteristics are similar to those observed in low temperature growth GaAs 2, and they demonstrate the potential of GaAs-on-silicon in high speed photoconductor applications. Our measurements indicated a bandwidth of at least 5 terahertz for this receiver.

© 1993 Optical Society of America