State filling dependent luminescence in hybrid tunnel coupled dot-well structures

A strong dependence of quantum dot (QD)–quantum well (QW) tunnel coupling on the energy band alignment is established in hybrid 'In''As'/'GA''AS'-'IN IND. x''GA IND. 1-x''AS'/'GA''AS' dot–well structures by changing the QW composition to shift the QW energy through the QD wetting layer (WL) energy. Due to this coupling a rapid carrier transfer from the QW to the QD excited states takes place. As a result, the QW photoluminescence (PL) completely quenches at low excitation intensities. The threshold intensities for the appearance of the QW PL strongly depend on the relative position of the QW excitonic energy with respect to the WL ground state and the QD ground state energies. These intensities decrease by orders of magnitude as the energy of the QW increases to approach that of the WL due to the increased efficiency for carrier tunneling into the WL states as compared to the less dense QD states below the QW energy.MWN - Material World NetworkNational Science Foundation of the U.S. (DMR-1008107)Deutsche Forschungsgemeinschaft (Li 580/8-1)Korea Foundation for International Cooperation of Science & Technology (Global Research Laboratory project - K20815000003)

Multilayers of InGaAs Nanostructures Grown on GaAs(210) Substrates

Multilayers of InGaAs nanostructures are grown on GaAs(210) by molecular beam epitaxy. With reducing the thickness of GaAs interlayer spacer, a transition from InGaAs quantum dashes to arrow-like nanostructures is observed by atomic force microscopy. Photoluminescence measurements reveal all the samples of different spacers with good optical properties. By adjusting the InGaAs coverage, both one-dimensional and two-dimensional lateral ordering of InGaAs/GaAs(210) nanostructures are achieved

Quantum Beats in Hybrid Metal–Semiconductor Nanostructures

We investigate nonradiative quantum coherence in the presence of coupling between excitons and surface plasmon polaritons (SPPs) in a hybrid metal–semiconductor nanostructure. In particular, we study how quantum coherence between heavy-hole (HH) and light-hole (LH) excitons in a GaAs quantum well (QW) is modified when they are coupled to SPPs of a gold grating. We find that the nonradative coherence is reduced in correlation with the coupling strength between the excitons and SPPs. Under the resonant coupling condition, the nonradiative coherence remains in the range of hundreds of femtoseconds, which is significantly longer than the plasmonic coherence. These experiments directly probe quantum dynamics in a prototypical hybrid system and provide critical information for exploring future quantum plasmonics applications

Tuning Quantum Dot Luminescence Below the Bulk Band Gap Using Tensile Strain

Self-assembled quantum dots (SAQDs) grown under biaxial tension could enable novel devices by taking advantage of the strong band gap reduction induced by tensile strain. Tensile SAQDs with low optical transition energies could find application in the technologically important area of mid-infrared optoelectronics. In the case of Ge, biaxial tension can even cause a highly desirable crossover from an indirect- to a direct-gap band structure. However, the inability to grow tensile SAQDs without dislocations has impeded progress in these directions. In this article, we demonstrate a method to grow dislocation-free, tensile SAQDs by employing the unique strain relief mechanisms of (110)-oriented surfaces. As a model system, we show that tensile GaAs SAQDs form spontaneously, controllably, and without dislocations on InAlAs(110) surfaces. The tensile strain reduces the band gap in GaAs SAQDs by ∼40%, leading to robust type-I quantum confinement and photoluminescence at energies lower than that of bulk GaAs. This method can be extended to other zinc blende and diamond cubic materials to form novel optoelectronic devices based on tensile SAQDs