Search

The degenerate four-wave mixing technique in the self-diffraction geometry is employed to investigate a novel GaAs/AlAs quantum well microstructure. Time-integrated transient measurements are carried out to study the coherent dynamics of excitons in a GaAs quantum well with AlAs islands inserted at the center of the well (IIQW) in excitation densities from 6×109to 1.5×1011cm-2. The decay of the time-integrated self-diffracted signal shows slower dephasing for the IIQW compared to that of a normal quantum well (NQW) without island insertion. The dephasing rate is found to increase slightly in the IIQW, while it is found to increase sharply in the NQW with the excitation density. A deep beat with a period of 1.45 ps, which disappears for co-circular polarization configuration, is observed in the decay of the self-diffracted signal in the IIQW. The detection-energy-resolved measurement reveals that the modulation of the beat increases up to full depth at low detection energy with respect to the peak energy of the self-diffracted signal. The dependence on detection energy and on polarization configuration shows that the beat is a quantum beat due to biexcitonic effect, which is enhanced by localization due to island insertion.

We report on molecular beam epitaxial (MBE) growth of high-quality In0.15Ga0.85As quantum wells (QWs) on (110) GaAs surfaces. The (110) surfaces are prepared by cleaving (001) GaAs substrates in air. The optimized growth condition is searched by changing the substrate temperature for the growth of In0.15Ga0.85As layers. We have found that the substrate temperature around 430°C is crucial to obtain the good surface morphology without facet structures and the sharp PL peak of an In0.15Ga0.85As QW.

Hot electrons were generated in n-doped GaAs/AlAs multiple quantum wells by optical intersubband excitation and their energy distributions were studied at 10 K. By measuring photoluminescence (PL) spectra, the hot-electron temperature Telwas quantitatively evaluated, taking into account such effects as the degenerate distribution of electrons, impurity-induced level broadening, and the distribution of holes. It was found that, when the intensity Pof the excitation was 30 kW cm-2, i.e. a few percent of the onset intensity for absorption saturation, Telincreased from 10 K to 120 K while the lattice temperature remained unchanged. When Pwas between 10 W cm-2and 30 kW cm-2, the rise of Telwas well explained by the balance between the photon energy absorption and the energy loss due to the LO phonon emission inside the ground subband.

The solid immersion lens has been applied to high-resolution microscopic photoluminescence (PL) imaging of a strip-line-patterned GaAs quantum well structure. An improved resolution corresponding to the numerical aperture of 1.25 was realized. The enhanced emission of PL from edges, and the significantly increased collection efficiency of PL were demonstrated.