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The optical properties of InAs/GaAs quantum well (QW) structures were studied by photoreflectance (PR) modulation spectroscopy, photoluminescence (PL) and atomic force microscopy. The transitions connected with a thin InAs/GaAs QW are visible for all samples.

Photoreflectance (PR) modulation spectroscopy, supported by photoluminescence (PL) and atomic force microscopy, was applied to the study of the optical properties of InAs/GaAs structures at the transition from the typical two-dimensional epitaxial growth to three-dimensional Stranski-Krastanov mode of InAs self-assembled quantum dot (QD) formation. Room temperature photoreflectance was measured on several molecular-beam epitaxy (MBE) grown structures, with growth conditions optimized for the 1.3 μm emission (an important window for telecommunication applications), differing in the nominal thickness of InAs layer from 1 to 2.5 ML (monolayer). The evolution of optical transitions connected with energy levels confined in a very thin InAs/GaAs quantum well was observed. For a small InAs nominal layer thickness (up to the critical thickness for the formation of three-dimensional islands), the heavy (light)-hole level to electron level transitions shift towards lower energy, indicating the increase in the quantum well width. When the nominal InAs layer thickness exceeds the critical value, the transition energies remain constant. It implies the formation of the so-called wetting layer, whose thickness is independent of the amount of deposited InAs material (fully driven by the strain). Its energy level structure was calculated (exploiting the effective mass approximation, with strain effects) in order to determine the actual wetting layer thickness, which was found to be approximately 1.6 ML. The features connected with the transitions between levels confined in QDs appear in PR and PL spectra for the amount of InAs material exceeding this number. The energies of the QD transitions shift to the red when the InAs layer nominal thickness is increased from 1.7 to 2 ML (indicating the increase in the average dot sizes) but remain constant for thicker layers, which is the evidence that the additional InAs material increases the density of QDs, but not their sizes. It points out at the existence of size limitation effect in the MBE growth of self-assembled QDs. [ABSTRACT FROM AUTHOR]

Nitrogen incorporation behavior in GaNAs bulk layers and GaInNAs quantum wells (QWs), grown by metalorganic chemical vapor deposition is discussed. The optical quality of the quantum wells is linked to the abruptness of the QWs and the nitrogen content.

Exciton and biexciton dynamics in a single self-assembled InAs/In0.53Ga0.23Al0.24As/InP(001) quantum dash emitting near 1.55 μm has been investigated by micro-photoluminescence and time-resolved micro-photoluminescence at T = 4.2 K. The exciton and biexciton fine structure splitting of ∼60 μeV, the biexciton binding energy of ∼3.5 meV, and the characteristic exciton and biexciton decay times of 2.0 ± 0.1 ns and 1.1 ± 0.1 ns, respectively, have been determined. The measurement of the biexciton and exciton cross-correlation statistics of the photon emission confirmed the cascaded relaxation process. The exciton-to-biexciton decay time ratio and a small fine structure splitting suggest carrier localization within the investigated quantum dash. [ABSTRACT FROM AUTHOR]

Carrier relaxation dynamics in self-assembled InAs/Ga0.2In0.8As0.4P0.6/InP(001) quantum dashes (QDashes) has been studied by degenerated time-resolved pump-probe and non-resonant photoluminescence spectroscopy at low temperature. These experiments yielded information about the exciton ground-state recombination lifetime reaching ∼1.75 ns. Additionally, the excited-to-ground state relaxation time has been measured to increase significantly from ∼40 ps up to ∼250 ps with the QDash size. Slow down of the intra-band relaxation time is interpreted in terms of the internal dash-to-dash energy-band-structure variation. The carrier dynamics in this case is most likely governed by the acoustic-phonon-mediated scattering processes. [ABSTRACT FROM AUTHOR]

Photoreflectance (PR) measurements have been performed on InAs/In0.53Ga0.23Al0.24As quantum dashes (QDashes) molecular-beam epitaxy grown on InP substrate. The PR features related to all relevant parts of the structure have been detected, including the ground and excited state optical transitions in QDashes. QDash ground state transition shifts from 1.5 to almost 2 μm with the increase in the thickness of InAs layer, corresponding to the increase in the average size of the dashes. Excited state transitions have been clearly observed at the energy of about 150 meV above the ground state transition energy. [ABSTRACT FROM AUTHOR]