Optical-microwave interactions in semiconductor devices

The study of injection-laser mode locking was continued. The lasers were operated in the external cavity configuration using a piece of optical fiber. Pumping injection lasers with short electrical pulses at a frequency corresponding to the round-trip transit frequency of the cavity generated stable optical pulses. A modified GaAs FET structure was designed such that efficient optical coupling to the active region of the device causes a strong optical-microwave interaction in the device for high-speed optical detection, optical injection locking of oscillators and optical-microwave mixing in amplifiers. Liquid phase epitaxial growth was used to grow the necessary GaAs and Ga0.6Al0.4As layers on a semi-insulating substrate. Device fabrication is still in progress. Preliminary results showed that the devices exhibited a reasonable source-drain current versus source-drain voltage characteristic and are quite uniform over the entire wafer. A GaAs Gunn diode was designed and fabricated during the quarter. The diodes will be used to study the interaction between the injection laser's output and the high field Gunn domain in the diode. The ultimate goal is to achieve the efficient high-speed pulsed modulation of injection lasers. Diodes with various lengths were fabricated and tested using a curve tracer. Differential negative resistance was observed in all the diodes tested.