Monolithically-integrated optoelectronic circuit for ultrafast sampling of a dual-gate field-effect transistor

An integrated optoelectronic circuit for ultrafast sampling of multi-terminal devices is described. This is achieved using optimized photoconductive switches fabricated from low-temperature-grown GaAs, monolithic integration of the device with the sampling circuit, control of the electromagnetic modes propagating on the coplanar waveguide using microfabricated airbridges, and discrimination of guided and freely-propagating modes using a novel electrooptic sampling method. As an example, the scattering parameters associated with the propagation of a picosecond pulse through one of the gates of a dual-gate heterojunction field-effect transistor are obtained at frequencies up to 300 GHz. The inter-gate capacitance is determined by measuring the electromagnetic transient coupled between the gates.