P. Basmaji

Exciton localization and temperature stability in self‐organized InAs quantum dots

We investigated the temperature effect on exciton localization in self‐organized InAs quantum dots. Quenching energy for excitons in reference quantum well and quantum dots was found to be 2 and 7 meV, respectively. Thermoactivation energy of electron‐hole emission through a GaAs barrier in the quantum dots was measured as 46 meV. We observed an unusual decrease of photoluminescence peak full width at half maximum with temperature, suggesting suppression of nonpredominant size quantum dot emissions due to carrier tunneling between nearby dots.

High index orientation effects of strained self‐assembled InGaAs quantum dots

Optical characterization of strained InGaAs/GaAs quantum dots grown by molecular beam epitaxy on (001) and (n11)B, where n=1, 2, 3, 5, and 7 orientations is reported in this work. Quantum dot photoluminescence emission shows remarkable orientation effects, presented in peak shape, full width at half‐maximum, and integrated intensity. Quantum dots grown on the (711)B plane demonstrate high quantum efficiency: integrated photoluminescence ratio between quantum dots and quantum well is about 10. Our results indicate an enhancement of the quantum dots onset thermal quenching energy by a factor of 2.5 for all orientations. Activation energy for thermal stimulated electron–hole emission in quantum dots is 2–5 times higher than in quantum wells. Photoluminescence polarization measurements show strong in‐plane dependence caused by the quantum dots’ structural anisotropy.

Self-organized InGaAs quantum dots grown by molecular beam epitaxy on (100), (711)AB, (511)AB, (311)AB, (211)AB, and (111)AB oriented GaAs

In this paper, we report optical properties of InGaAs quantum dots grown by molecular beam epitaxy on GaAs (n11)AB, where n is 1, 2, 3, 5 and 7, and reference (100) substrates. A higher crystal quality of quantum dots has been detected on (n11)B surfaces due to the strong integrated photoluminescence (PL) intensity, its value on (711)B orientation being 10 times larger than the QW one. Quantum dots grown on a (311)B surface showed a higher homogeneity in size. The quantum well PL peak position reveals a non-monotonical red-shift when the surface direction changes from (100) to (111).

Photoreflectance measurements on Si δ‐doped GaAs samples grown by molecular‐beam epitaxy

We investigate δ‐doped GaAs samples grown by molecular‐beam epitaxy with different silicon areal concentration and cap layer thickness, using photoreflectance spectroscopy. The features observed on the high‐energy side of the fundamental gap are attributed to transitions involving electronic sub‐bands in the δ‐doped potential well that take into account the diffusion of the dopants.

CHARACTERIZATION OF GAAS WIRE CRYSTALS GROWN ON POROUS SILICON BY RAMAN SCATTERING

We measured the Raman spectra of GaAs wirelike crystals grown on porous silicon (PS) using two different excitation radiations which probe the near surface and the bulk. The transverse optic and longitudinal optic vibrational bands appear redshifted and broadened when compared to bulk GaAs, and with shoulders on their low frequency sides. These features are attributed to a disorder-induced relaxation in the selection rules for Raman activity arising from point defects. In addition, the bands show a strong frequency and bandwidth dependence on excitation energy. Differences in penetration depth together with a gradient in defect density are invoked to account for the observations. This analysis yields a picture in which there is a predominantly amorphous GaAs region buried at the PS–GaAs interface followed by microcrystalline GaAs cylindrical structures that become less defective as they grow farther from the interface. The near surface tends to approach the low defect density of crystalline GaAs.

Negative differential magnetoresistance and commensurability oscillations of two-dimensional electrons in a disordered array of antidots

Negative linear magnetoresistance of two-dimensional (2D) electrons have been found in a disordered array of antidots. The authors suggest that trajectories that roll along the array of antidots exist in a magnetic field. These trajectories have a mean free path larger than the average value for electrons with ordinary diffusion.

Electronic transport in periodically δ‐doped GaAs layers

We investigate periodically silicon δ‐doped GaAs sample grown by molecular‐beam epitaxy using magnetoresistance measurements. Transport measurements give evidence for quantum confinement of the electronic gas in the layer. Thomas–Fermi approximation is used in order to assess the various subband densities.

Anisotropy investigations and photoluminescence properties of porous silicon

Abstract Porous silicon layers have been investigated using reflectance and photoluminescence techniques at room and liquid nitrogen temperatures. We observe a noticeable anisotropy of porous silicon samples. The measured parallel and normal components of the refractive index for samples with moderate porosity were 1.25 and 1.30, respectively. Possible mechanisms for the origin of the photoluminescence are discussed.

Raman study of the topology of InAs/GaAs self-assembled quantum dots

The topology of self-assembled InAs/GaAs quantum dots was studied by resonant Raman scattering caused by the interface modes localized near the edges of the dots. Evidences were found that on both sides of the InAs layer containing the dots, their topologies show some resemblances. In addition, in the multilayered systems the evidence of the coalescence of the dots (which form vertical columns) in neighbor layers separated by the distance smaller than 25 monolayers was obtained.

Molecular-beam epitaxy of self-assembled InAs quantum dots on non-(1 0 0) oriented GaAs

In this paper we report optical properties of InAs quantum dots (QD) grown by molecular-beam epitaxy on GaAs (2 1 1)A, (n 1 1)A/B, where n is 1, 5 and 7, and on reference (0 0 1) substrates. The photoluminescence (PL) spectra reveal differences in amplitude, integral luminescence, peak position and shape. Temperature dependence indicates an additional lateral confinement on (0 0 1), (n 1 1)B, (2 1 1)A and (1 1 1)A substrates. Our results also show an enhancement of QD onset thermal quenching energy by a factor of ∼ 3 for these orientations, when compared with the reference quantum well. PL polarization measurements show strong in-plane dependence caused by the quantum dots structural anisotropy. However, the structure grown on (5 1 1)A and (7 1 1)A surfaces does not exhibit QD formation.