InAs quantum dots with size fluctuations of less than 4% were grown on GaAs using the self-assembling method. By covering the quantum dots with In0.2Ga0.8As or In0.2Al0.8As, strain in InAs dots can be partly reduced due to relaxation of lattice constraint in the growth direction. This results in low-energy emission (about 1.3 μm) from the quantum dots. The photoluminescence linewidth can be reduced to 21 meV at room temperature. This width is completely comparable to the theoretical limit of a band-to-band emission from a quantum well at room temperature. Because the dots can be uniformly covered by the strain reducing layers, factors that degrade size uniformity during coverage, such as compositional mixing or segregation, will be suppressed, allowing for an almost ideal buried quantum dot structure.

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The cAMP cascade and vascular endothelial growth factor (VEGF) are critical modulators of depression. Here we have tested whether the antidepressive effect of the cAMP cascade is mediated by VEGF in the adult hippocampus. We used a conditional genetic system in which the Aplysia octopamine receptor (Ap oa 1 ), a G s -coupled receptor, is transgenically expressed in the forebrain neurons of mice. Chronic activation of the heterologous Ap oa 1 by its natural ligand evoked antidepressant-like behaviors, accompanied by enhanced phosphorylation of cAMP response element-binding protein and transcription of VEGF in hippocampal dentate gyrus (DG) neurons. Selective knockdown of VEGF in these cells during the period of cAMP elevation inhibited the antidepressant-like behaviors. These findings reveal a molecular interaction between the cAMP cascade and VEGF expression, and the pronounced behavioral consequences of this interaction shed light on the mechanism underlying neuronal VEGF functions in antidepression.

Phonon resonances observed in the photoluminescence ͑PL͒ spectra of InP and In 0.35 Ga 0.65 As selfassembled quantum dots ͑QD's͒ in an external electric field are studied in detail. The resonances are shown to arise from fast phonon-assisted relaxation of hot carriers, and to become observable when the PL is quenched by nonradiative losses from excited states. A simple model is developed that considers tunneling of the carriers from the QD's into the barrier layer as the main process responsible for PL quenching in the presence of an electric field. From this model, the depth of the potential well for holes is estimated to be 10-20 meV for the InP QD's. The PL kinetics measurement is performed with a time resolution of 6 ps. Clear evidence of surprisingly fast carrier relaxation with emission of high-energy acoustic phonons is found. Further acceleration of the carrier relaxation is observed under strong optical pumping. We consider this effect to be caused by Auger-like carrier-carrier scattering processes. Acceleration of the relaxation observed at elevated temperatures is ascribed to stimulated phonon emission.

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