Quantum Optoelectronics

Abstract:

There is much current interest in determining the energy relaxation processes of hot carriers confined in quantum well heterostructures. We present measurements of time-resolved photoluminescence from hot carriers and from carrier recombination at shallow traps. The experimental technique is basically the same as described previously except that the laser (h upsilon //L equals 1. 76 eV) excites carriers only in the GaAs layers.

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.

Abstract:

We report the first picosecond time-resolved photoluminescence measurementsof hot-carrier relaxation in a modulation-doped GaAs-GaAlAs MQW in the presence of strong magnetic fields. We have measured the lifetimes of carriers in excited Landau levels and have determined the time-dependent carrier temperature. We find that the cooling rate is slower in applied field tthan at B=0; also there is a significant increase in the cooling rate for B {greater-than or approximate} 10T. We report also the observation of highly time-dependent linewidths of the Landau levels. © 1985.

Abstract:

The dynamics of photoexcited carriers in direct gap semiconductors can now be measured directly by time-resolved spectroscopy using intense, ultra-short laser pulses. High carrier densities can be generated and the processes of carrier cooling and recombination can be investigated by measuring band-edge transient absorption and luminescence. At high carrier densities a Mott transition is expected to occur when the interparticle separation r//s congruent 2. 5 a//o , where a//o is the exciton radius, so that for lower values of r//s dramatic changes in the band-edge absorption spectrum are expected. We report measurements of the layered semiconductor GaTe. The chief interest in this material is, as with other III-VI semiconductors, the strong excitonic behaviour exhibited at low temperature.