E. Petitprez

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).

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.

Strain relaxation-induced modifications of the optical properties of self-assembled InAs quantum dot superlattices

We have investigated self-assembled InAs quantum dot superlattices using photoluminescence and transmission electron microscopy. We report results regarding the influence of the dot vertical separation on the optical properties of such structures. The photoluminescence peak shifts toward higher energies and its intensity drops by one order of magnitude when the distance between two consecutive quantum dot layers is reduced below 70 A. Our transmission electron microscopy images suggest that such unexpected photoluminescence features are related to the formation of structural defects induced by the large amount of strain relieved at small dot separations.

Electronic coupling and thermal relaxation in self-assembled InAs quantum dot superlattices

We report optical and structural characterizations of InAs quantum dot superlattices grown by molecular beam epitaxy on GaAs (001). Cross-sectional electron microscopy imaging reveals ~ 20 nm diameter InAs islands well aligned along the growth direction. Low temperature photoluminescence spectra exhibit a clear redshift with decreasing island vertical separation, as a result of electronic coupling between stacked dots, given that the larger shift is obtained for 70 A spacing. At high excitation power, the photoluminescence spectra show a doublet structure corresponding to coupled and uncoupled quantum dot states. The temperature dependence of the photoluminescence indicates that thermionic emission activation energy is much lower than the estimated barrier height. Such a difference is explained by the presence of non-radiative recombination centers due to strain relaxation and In segregation.

Optical properties of vertically stacked InAs island layers grown on (311)A/B and (001) GaAs substrates

Abstract The optical properties of vertically stacked InAs island layers grown by molecular beam epitaxy on (311)A/B and (001) GaAs substrates have been studied by means of photoluminescence (PL) and transmission electron microscopy (TEM) measurements. These properties were systematically investigated as a function of spacer layer thickness, orientation, and temperature. Spacer layer thickness variation exhibits influence on PL spectra for all orientations. Differences in peak shape, position, amplitude and integrated photoluminescence have also been observed for all surfaces. The results show an increase of integrated PL intensity of ∼5 times and a decrease of spectral linewidth compared with a single set of islands, suggesting a possible electronic coupling between the layers. In addition, in the case of (311)A, the structure does not exhibit QD formation.