In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the
science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such
as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies
have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs
ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers
and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW
where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the
differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly
influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as
the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our
measured T1 is comparable to the reported measurements in MBE grown InMnAs and several time resolved
measurements on InAs.
We have generated pulsed beams of longitudinal and transverse polarized acoustic phonons by ultra fast optical excitation of gallium arsenide/aluminium arsenide superlattice structures. The phonons propagated ballistically over macroscopic (~ mm) distances at low temperatures and were detected using superconducting bolometers. We used superlattice phonon filters and the frequency-dependent phonon scattering in gallium arsenide to analyse the phonon spectrum. The phonons were found to be monochromatic, with a centre frequency given by υ = cs/dSL, where cs is the phonon speed and dSL is the superlattice period, and having a spectral line width (full width at half maximum) of less than 50 GHz. We measured a mean free path of 0.8 mm for both the longitudinal and transverse modes, consistent with point defect scattering in the GaAs substrate. Such phonons, with frequencies in the THz range, have potential applications in a number of areas, e.g. acoustic microscopy of solid-state nanostructures.