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We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL) measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness. [ABSTRACT FROM AUTHOR]

InAs quantum-dot structures were grown using a GaAs1-xSbx matrix on a GaAs(001) substrate. The use of GaAs1-xSbx for the buffer and cap layers effectively suppressed coalescence between dots and significantly increased the dot density. The highest density (~3.5 x 1011/cm²) was obtained for a nominal 3.0 monolayer deposition of InAs with an Sb composition of x = 13-14% in the GaAs1-xSbx matrix. When the Sb composition was increased to 18%, the resulting large photoluminescent red shift (~90 meV) indicated the release of compressive strain inside the quantum dots. For x > 13%, we observed a significant decrease in photoluminescence intensity and an increase in the carrier lifetime (≥4.0 ns). This is attributed to the type-II band alignment between the quantum dots and matrix material. [ABSTRACT FROM AUTHOR]

The authors report on the formation, structural analyses, and optical properties of GaInP/GaP self-catalyzed core-shell double heterostructure nanowires (NWs) grown on Si(111) substrates. The NW growth is initiated with the formation of Ga droplets as catalysts, followed by the growth of GaP core and GaInP double heterostructure shells. Structural analyses elucidate the existence of interfaces among GaP core and GaInP double heterostructure shells. Light emissions at 640 and 800 nm are observed at 77 K from GaInP core-shell double heterostructure NWs and surface states of GaInP layers, respectively. The signal from the surface state can be mitigated via surface passivation with ammonium sulfide solution. These results will enable the realization of novel NW-based light-emitting diodes or nanolasers grown on Si substrates utilizing mature Si technologies. [ABSTRACT FROM AUTHOR]

We describe in situ nanoscale etch-pit formation on GaSb (100) surfaces as a result of exposure to an As2 flux in molecular beam epitaxy. The pits form as a result of an Sb-displacement reaction that occurs between the GaSb substrate and the impinging As adatoms. The nanoscale surface features are highly crystallographic with a strong preference for {111} planes, similar to other etching techniques. Nanopit dimensions and density increase with As exposure time. For the 60 s exposure analyzed in this article, the pits vary in both size and shape with average dimensions ∼25 nm wide and 50–80 nm long and 10–70 nm deep, with density of ∼1×109/cm2. Subsequent GaAs overgrowth proceeds by a coalescence mechanism leaving interfacial nanovoids and finally highly planar bulk layers. [ABSTRACT FROM AUTHOR]

We analyze temperature-dependent photoluminescence (PL) behavior of patterned InAs/GaAs quantum dots (PQDs) formed by selective area epitaxy using metalorganic chemical vapor deposition. The processing scheme, described here, yields an ensemble of electronically isolated PQDs with PL characteristics that significantly differ from self-assembled (SA) QDs since neither a wetting layer nor neighboring QDs are available for coupling. The isolated nature of the PQDs supports a non-Fermi (nonequilibrium) carrier distribution which yields very different PL characteristics compared to the Fermi (equilibrium) distribution of the SAQDs especially at temperatures >100 K. Thus, the PQDs demonstrate a constant PL linewidth within the temperature range of 80–300 K along with improved temperature stability of PL intensity in comparison to SAQDs. The increased temperature stability allowed by electronic isolation may prove very important for high speed, temperature-insensitive QD laser development. [ABSTRACT FROM AUTHOR]

We discuss the results of a growth matrix designed to produce high quantum dot (QD) density, defect-free QD ensembles, which emit at 1.3 µm using metalorganic chemical vapor deposition (MOCVD). In our study, we balance the nucleation rate and adatom surface migration to achieve high surface densities (1 × 10[sup 11] dots/cm²) and avoid QD coalescence or defects that commonly characterize MOCVD-grown QD ensembles designed for longer wavelength emission. Room-temperature photoluminescence (PL) spectra from corresponding surface QDs depend on QD size and density and show an emission wavelength up to 1600 nm. Ground-state PL from capped QDs is measured at 1.38 µm with a 40 meV linewidth. We demonstrate the ground-state 1.3 µm electroluminescence from a QD light-emitting diode structure grown on n-type GaAs. [ABSTRACT FROM AUTHOR]

A method that reduces the lattice mismatch between the InAs quantum dots (QDs) and their surrounding material to extend the GaAs based QD emission wavelength is proposed. The density and the ground state transition of the resulting QD ensemble are lined out.

Presents information on a study which described the near-threshold transverse modes in AlAs/GaAs/InGaAs vertical-cavity surface-emitting lasers with different Bragg reflector systems. Temperature dependence of the lasing mode; Aspects of the lasing behavior; Experimental details; Results and discussion; Conclusions.

Presents an analysis of room temperature spontaneous emission in AlGaAs/GaAs Fabry-P é rot vertical cavities with thin GaAs active regions. Calculations of the spontaneous emission characteristics for semiconductor microcavity structures; Facts on the measured transmission spectrum of the vertical cavities; Effects of the precise placement and thickness of the GaAs active region on spontaneous emission.

The photon density required for the saturation of normal-mode coupling in oxide-apertured nanocavities is measured to be 90 photons/μm2 by pump-probe experiments. The photon number is only 300 for a semiconductor nanocavity with a 2 μm diameter aluminum-oxide aperture, drastically reduced from 200 000 for a 50 μm waist on a planar microcavity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]