P. P. Gonzalez-Borrero

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.

Correlation between structural and optical properties of InAs quantum dots along their evolution

Abstract The growth of highly inhomogeneous samples is presented as a suitable way to investigate the continuous evolution of self-assembled InAs quantum dots as a function of the thickness of deposited material. A single specific sample allowed a direct comparison of the structural and optical properties of the strained islands using atomic-force microscopy and low-temperature photoluminescence.

Influence of surface structure on segregation and alloy properties in (100)- and (311)-oriented InGaAsGaAs heterostructures

Abstract The influence of surface orientation and surface structure on indium segregation and alloy properties were systematically studied in InGaAs GaAs quantum well structures grown by molecular beam epitaxy. (100), (311)A and (311)B surface orientations and different approaches in the growth interruption at the interfaces were used in this investigation. The segregation process and alloy parameters were obtained by photoluminescence and RHEED measurements. We find significant differences in the optical properties and growth kinetic for the three orientations. Using growth interruption we were able to change the surface structure and reduce the segregation process for all orientations.

Electron beam lithography-based InGaAs/GaAs quantum dot arrays on (311)A gaas surfaces

The development of techniques of nanofabrication is presented, using electron beam lithography, applied to semiconductor heterostructures grown by molecular beam epitaxy on non-(100) substrates. The structures studied were fabricated on InGaAs/GaAs single quantum wells, with 15% In concentration and a well width of 4 nm. The arrays of quantum dots were studied by photoluminescence spectroscopy. The optical emission spectra were analyzed with regard to the dot parameters, power density and temperature.

Photoluminescence study of spin - orbit-split bound electron states in self-assembled InAs and quantum dots

The photoluminescence of electron excitations was measured in InAs and self-assembled quantum dot systems. For the first time spin - orbit-split excitons were observed in resonant photoluminescence when the excitation energy was close to the exciton energy; off-resonant photoluminescence spectra reveal heavy-hole excitons.

Study of the spontaneous alignment of InAs quantum dots along the surface steps as a function of the InAs coverage

The evolution of InAs quantum dots (QDs) deposited on GaAs (001) was investigated in a continuous and unambiguous way as a function of the InAs coverage. Taking advantage of the intrinsic non-uniformity of the In flux in the molecular beam epitaxy system, a single sample was grown where the amount of InAs material varied in a monotonic way along the sample area. High-quality atomic force microscopy (AFM) images showed a saturation of the number of QDs nucleated out of the surface steps as the system evolved and confirmed that QDs can be effectively aligned along the surface steps up to the highest densities, which is an important subject for device application.

Light Emitting Diodes Based on Self-Assembled InAs Quantum Dots Grown on GaAs (311)A Surfaces Using only Si as a Doping Material

InAs self-assembled quantum dots have been grown on GaAs (311)A surfaces, and used as an active layer inside a p-n junction to produce light emitting diode (LED) structures. The p and n regions were doped only with Si under special molecular beam epitaxy conditions. The LED properties were studied using conventional optical and electrical techniques.