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We present eight-band k·p calculations of the electronic and polarization properties of columnar InzGa1-zAs quantum dots (CQD) with high aspect ratio embedded in an InxGa1-xAs/GaAs quantum well. Our model accounts for the linear strain effects, linear piezoelectricity, and spin-orbit interaction. We calculate the relative intensities of transverse-magnetic (TM) and transverse-electric (TE) linear polarized light emitted from the edge of the semiconductor wafer as a function of the two main factors affecting the heavy hole—light hole valence band mixing and hence, the polarization dependent selection rules for the optical transitions, namely, (i) the composition contrast z/x between the dot material and the surrounding well and (ii) the dot aspect ratio. The numerical results show that the former is the main driving parameter for tuning the polarization properties. This is explained by analyzing the biaxial strain in the CQD, based on which it is possible to predict the TM to TE intensity ratio. The conclusions are supported by analytical considerations of the strain in the dots. Finally, we present the compositional and geometrical conditions to achieve polarization independent emission from InGaAs/GaAs CQDs. [ABSTRACT FROM AUTHOR]

Thermal annealing effects of a GaAs0.909Sb0.07N0.021 film grown on GaAs substrate via gas-source molecular beam epitaxy have been characterized by photoluminescence (PL) and photoreflectance (PR) techniques. PL measurements show the evolution of luminescence feature with the thermal annealing treatment. The conduction to heavy-hole (HH) band and conduction to light-hole (LH) band transitions originated from the strained induced valence band splitting in GaAs0.909Sb0.07N0.021 layer have been observed by the PR measurements. The near band edge transition energies are slightly blueshifted, and the splitting of HH and LH bands is reduced with rising annealing temperature. The temperature dependences of near band edge transition energies are analyzed using Varshni and Bose–Einstein expressions in the temperature range from 15 to 300 K. The parameters that describe the temperature variations of the near band edge transition energies are evaluated and discussed. [ABSTRACT FROM AUTHOR]

GaNAs(Sb) layers were grown by solid-source molecular-beam epitaxy utilizing a radio frequency (rf) nitrogen plasma source. The samples contained less nitrogen and antimony (0.5%–0.8% N and <=2% Sb) than in previous studies and were examined for their optical and electronic properties and any interactions between the elements. Secondary-ion-mass spectrometry, high-resolution x-ray diffraction, electroreflectance (ER) spectroscopy, and photoluminescence (PL) measurements were used to study those properties. We found that the addition of small amounts of antimony enhanced nitrogen incorporation into GaAs, similar to other studies that used 5–15× the mole fraction of antimony. The nitrogen concentration increased with increasing antimony flux. PL measurements indicated an improvement in optical quality with increasing nitrogen and antimony concentrations—contrary to the belief that adding more nitrogen necessarily degrades material quality. We collected and simulated ER spectra to examine the general band properties of the layers. Isoelectronic codoping can explain the improved quality when antimony is added to GaNAs. The improvement in GaNAs with small amounts of antimony holds great promise for improving strain-compensated GaInNAs(Sb)/GaNAs devices. [ABSTRACT FROM AUTHOR]

Thermal annealing effects of a Ga[As.sub.0.909][Sb.sub.0.07][N.sub.0.021] layer grown by gas-source molecular beam epitaxy are characterized by photoluminescence (PL) and photoreflectance (PR) techniques. The PL and PR measurements have shown the evolution of luminescence feature with the thermal annealing treatment and the conduction to heavy-hole band and conduction to light-hole band transitions originated from the strained induced valence band splitting in this layer.

The molecular beam epitaxy grown structures are investigated, comprising of InGaAs quantum wells (QW) separated by a thin InGaAlAs barrier from InAs quantum dots (QDs), emitting at 1.55 μm, grown on an InP substrate. To control the coupling between QW and QD parts the thickness of the barrier is changed, which commands the wave function overlap. The tuning of that parameter allows for the study of the influence of the QW potential on the energy structure of states and their wave functions in QDs, changing from an uncoupled system, where the optical response is just a sum of responses from two isolated elements, to a strongly quantum mechanically coupled system, exhibiting mixed 2D‐0D characteristics. The changes of the energy structure that are deduced from the photoreflectance and photoluminescence spectroscopy results, supported by 8‐band k · p modeling, explain the measured differences in the photoluminescence decay times between samples with different barrier thicknesses. [ABSTRACT FROM AUTHOR]