Quantum Optoelectronics

Abstract:

Time-resolved photoluminescence measurements of the layered semiconductors GaSe and GaTe have been made using a mode-locked dye laser a synchronously scanning streak camera. It is shown that at low excitation densities (1015-1017cm-3) exciton dynamics is dominated by trapping at defects. A rate equation model is developed that describes exciton formation, recombination and trapping. At 4K the authors determine free-exciton recombination times at 200 ps for GaTe and 350 ps for GaSe. Trapping times of 200 and 900 ps yield capture cross sections of 1.2*10-14cm2and 3.6*10-15cm2for GaTe and GaSe respectively. © 1987 IOP Publishing Ltd.

Abstract:

Picosecond time-resolved measurements of luminescence from hot carriers confined in GaAsGaAlAs multiple quantum wells show that energy loss rates are substantially slower than those predicted for 2D carriers. We review our recent experiments and present results for photoexcitation of (1) GaAs layers only, (2) both GaAs and GaAlAs layers. We compare the energy loss rates in samples with different well widths. Finally, we present measurements of hot 2D carrier relaxation in the presence of high magnetic fields; at low fields the energy loss rate is reduced, but for B > 9 T we observe a rapid increase. © 1986.

Abstract:

Domain wall structures in thin foils of a Ni-Fe-Co-Ti alloy have been determined using the differential phase contrast mode of Lorentz electron microscopy. Among the advantages of this mode are that easily interpretable signals can be obtained whilst the experiment is in progress. In accord with theoretical expectation the walls were found to have a vortex structure whose width increased linearly with foil thickness. © 1985.