Control of vertically coupled InGaAs/GaAs quantum dots with electric fields

Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.     

Characterization of (In,Ga)As/GaAs strained-layer multiple quantum wells with high-resolution X-ray diffraction and computer simulations

Pseudomorphic, highly strained (In,Ga)As/GaAs multiple quantum well structures were grown by molecular beam epitaxy and characterized by high-resolution X-ray diffraction. Thickness, lattice mismatch and chemical composition of the quantum wells were determined from measurements of satellite Bragg reflections and comparison with calculated rocking curves. In periodic structures, quantum wells with a width of less than 10 nm can be characterized by this technique. The results are compared with transmission electron microscopy, optical absorption and optical emission spectroscopy.     

Structural and optical analysis of size-controlled InAs quantum dashes

Self-organized InAs and InGaAs quantum dashes have been investigated by chemically sensitive scanning transmission electron microscopy and photoluminescence spectroscopy. The quantum dashes exhibit a triangular cross section. Using electron energy loss spectroscopy, we show that no intermixing between quantum dashes and embedding barrier occurs during growth. By adjusting the nominal thickness of the InAs layer, the emission wavelength of the InAs quantum dashes can be tuned between 1.37 and 1.9 μm in a straightforward way.     

STEM-study of 1.3 μm InAs/InGaAs quantum dot structures

We investigated InAs-Dots-in-a-well structures emitting near 1.3 μm by bright field and Z-contrast mode in a scanning transmission electron microscope. The chemically sensitive Z-contrast mode is found to give direct information on the actual position of the InAs-Dots inside the embedding well, while the bright field mode monitors the strain fields. Comparing a series of structures, we found that the most symmetric design is realized by an nominally asymmetric growth. These symmetric structures exhibit the best performance with respect to photoluminescence spectra and laser threshold current density.     

Electromodulation spectroscopy of In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum wells

In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As quantum wells (QWs) of various widths have been grown by molecular beam epitaxy on the InP substrate and investigated by electromodulation spectroscopy, i.e. photoreflectance (PR) and contactless electroreflectance (CER). The optical transitions related to the QW barrier and the QW ground and excited states have been clearly observed in PR and CER spectra. The experimental QW transition energies have been compared with theoretical predictions based on an effective mass formalism model. A good agreement between experimental data and theoretical calculations has been observed when the conduction band offset for the In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As interface equals 60%. In addition, it has been concluded that the conduction band offset for the In_0.53Ga_0.23Al_0.24As/InP interface is close to zero. The obtained results show that InGa(Al)As alloys are very promising materials in the band gap engineering for structures grown on InP substrate.     

Exciton-photon interaction in low-dimensional semiconductor microcavities

The structure of the photon states and dispersion of cavity polaritons in semiconductor microcavities with two-dimensional optical confinement (photon wires), fabricated from planar Bragg structures with a quantum well in the active layer, are investigated by measuring the angular dependence of the photoluminescence spectra. The size quantization of light due to the wavelength-commensurate lateral dimension of the cavity causes additional photon modes to appear. The dispersion of polaritons in photon wires is found to agree qualitatively with the prediction for wires having an ideal quantum well, for which the spectrum is formed by pairwise interaction between exciton and photon modes of like spatial symmetry. The weak influence of the exciton symmetry-breaking random potential in the quantum well indicates a mechanism of polariton production through light-induced collective exciton states. This phenomenon is possible because the light wavelength is large in comparison with the exciton radius and the dephasing time of the collective exciton state is long. Zh. éksp. Teor. Fiz. 114, 1329–1345 (October 1998)