ABSTRACT
At low temperatures free electrons and holes condense into free excitons, which are electrically neutral, and are thus unobservable in conventional, electrical transport measurements. To study the physical limitations of low-temperature, high-mobility transport the authors have resorted to a new all-optical, time-resolved photoluminescence (PL) confocal imaging technique which is sensitive to both charged and neutral-particle transport. Conventional transport techniques attempt to study the absolute physical mobility limitations through growth of special heterostructures, modulation-doped structures. The authors conclude that the high-mobilities for joint neutral-particle (excitonic) and free carrier (electron and/or hole) transport are the result of diminished charged-center scattering and the simulation of modulation-doping which photoexcitation creates in the screening out of charged centers — thus resultant mobilities are limited only by intrinsic lattice (deformation potential) scattering. These results are the subject of further study in an effort to additionally elucidate the observed dynamics.
