Carrier dynamics in III-V materials and hetero-structures studied by ultrafast laser techniques.

The properties of a new class of materials grown by molecular beam epitaxy at very low substrate temperatures, as pertains to their carrier dynamics, is discussed. Using a transient optical reflectance and absorption technique, based on femtosecond dye and Ti-saphhire lasers, sub-picosecond carrier lifetimes have been confirmed, for the first time, in GaAs and InAlAs grown at temperatures of near 200$\sp\circ$C. Preliminary investigations indicate similar trends in the InGaAs/InP material system. The same materials have also been used as laser triggered photoconductive switches for the generation of electrical pulses as short as 0.5 picosecond in duration, measured using electro-optic and photoconductive sampling techniques. These materials also find use in other ultrafast optoelectronic applications such as sub-picosecond electronic sampling gates, high speed photodetectors, terahertz radiating antennas etc. Using the above generated electrical pulses, the propagation characteristics of coplanar interconnects have been studied upto terahertz bandwidths. The role of modal dispersion and radiation loss is experimentally and theoretically verified. The optical properties of high quality lattice-matched InGaAs/InAlAs multi-quantum wells (MQW) has been studied. The narrowest photoluminescence linewidth to date, of 5.7 meV is reported, and excitonic resonances of upto n = 3 energy sub-level are observed at room temperatures. Using a time-resolved non-linear photoluminescence correlation technique, the carrier dynamics in this material has been studied. An all-optical time-of-flight technique with single picosecond temporal resolution has been developed for studying electronic transport. The perpendicular transport as a function of the electric field, has been studied in a graded band-gap structure and multi-quantum well structures based on the GaAs and InP material system. The carrier escape out of the quantum well due to a thermally assisted tunneling process is believed to be the limiting mechanism for transport in an MQW. Thinner and shallower barriers are therefore required for higher speed operation in devices using perpendicular transport across an MQW region. The development of a tunable femtosecond color center laser for optoelectronic applications around the 1.5 $\mu$m wavelength region is also discussed.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105904/1/9226909.pdfDescription of 9226909.pdf : Restricted to UM users only