Island scaling in strained heteroepitaxy: InAs/GaAs(001)

Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

Epitaxially grown quantum dots (QDs) are established as quantum emitters for quantum information technology, but their operation under ambient conditions remains a challenge. Therefore, we study photoluminescence (PL) emission at and close to room temperature from self-assembled strain-free GaAs quantum dots (QDs) in refilled AlGaAs nanoholes on (001)GaAs substrate. Two major obstacles for room temperature operation are observed. The first is a strong radiative background from the GaAs substrate and the second a significant loss of intensity by more than four orders of magnitude between liquid helium and room temperature. We discuss results obtained on three different sample designs and two excitation wavelengths. The PL measurements are performed at room temperature and at T = 200 K, which is obtained using an inexpensive thermoelectric cooler. An optimized sample with an AlGaAs barrier layer thicker than the penetration depth of the exciting green laser light (532 nm) demonstrates clear QD peaks already at room temperature. Samples with thin AlGaAs layers show room temperature emission from the QDs when a blue laser (405 nm) with a reduced optical penetration depth is used for excitation. A model and a fit to the experimental behavior identify dissociation of excitons in the barrier below T = 100 K and thermal escape of excitons from QDs above T = 160 K as the central processes causing PL-intensity loss.

Morphology and valence band offset of GaSb quantum dots grown on GaP(001) and their evolution upon capping

This work presents a detailed study of GaSb quantum dot (QD) epitaxy on (001) GaP substrates by means of molecular beam epitaxy. Despite the large mismatch between GaP and GaSb, we show that in the nucleation-diffusion regime, the QD size distribution follows the predictions of the scaling theory. Scanning transmission electron microscopy analysis of grown QDs reveal that they are plastically relaxed by 60° pairs of misfit dislocations and the valence band offset measured by x-ray photoelectron spectroscopy on such QDs amounts to 0.5 eV. After capping, the QD morphology is strongly modified with a large P/Sb exchange-segregation reaction, which even leads to the formation of core-shell nanostructures. Remarkably the resulting QD layer is coherent to the substrate without any remaining misfit dislocation and exhibits still strong composition modulations.

SURFACE MORPHOLOGY EVOLUTION OF STRAINED InAs/GaAs(331)A FILMS

Surface morphology evolution of strained InAs/GaAs (331) A films was systematically investigated in this paper. Under As -rich conditions, InAs elongated islands aligned along [Formula: see text] are formed at a substrate temperature of 510°C. We explained it as a result of the anisotropic diffusion of adatoms. Under In -rich conditions, striking change has occurred with respect to the surface morphology of the InAs layers. Instead of anisotropic InAs elongated islands, unique island-pit pairs randomly distributed on the whole surface were observed. Using cooperative nucleation mechanisms proposed by Jesson et al. [Phys. Rev. Lett.77, 1330 (1996)], we interpret the resulting surface morphology evolution.

Spacing distribution functions for the one-dimensional point-island model with irreversible attachment

We study the configurational structure of the point-island model for epitaxial growth in one dimension. In particular, we calculate the island gap and capture zone distributions. Our model is based on an approximate description of nucleation inside the gaps. Nucleation is described by the joint probability density p(n)(XY)(x,y), which represents the probability density to have nucleation at position x within a gap of size y. Our proposed functional form for p(n)(XY)(x,y) describes excellently the statistical behavior of the system. We compare our analytical model with extensive numerical simulations. Our model retains the most relevant physical properties of the system.

Island-Size Distributions for Submonolayer Epitaxy: Rate Equations and Beyond

The scanning tunnelling microscope has revolutionized the quantitative analysis of epitaxial phenomena. This, in turn, has spawned a huge theoretical effort aimed at analyzing various aspects of the morphology of growing surfaces. One of the most important general approaches to have emerged from this effort is based on the application of scaling concepts to epitaxial island-size distributions in the regime of submonolayer coverage prior to coalescence. We first discuss the analytical basis for scaling solutions to rate equations. In the limit of irreversible aggregation, a solution is obtained in terms of the capture numbers which agrees with previous work. For reversible aggregation, we identify a new quantity that may be regarded as a continuous analogue of a critical island size. We then examine the influence of spatial correlations by introducing a method for modeling epitaxial phenomena in terms of the motion of island boundaries, which is implemented numerically using the level set method. This island dynamics model is continuous in the lateral directions, but retains atomic scale discreteness in the growth direction. Several choices for the island boundary velocity are discussed and computations of the island dynamics model using the level set method are presented.

Nucleation of Islands During Epitaxial Growth: Influence of a Second Species

The theory of the nucleation and growth of islands is maturing rapidly. This advance is driven by the increased availability of experimental data, as well as the need for better control over growth processes. Recently, a number of authors have studied the effects of introducing a second species onto the surface in order to influence the ultimate growth morphology. In some situations, the addition of a second species results in a signficant change (approximately a factor of 1000) in the nucleated island density. The origin of this increase in density has been linked to the anomalous diffusion induced by the presence of the additional species of atoms. In the current paper, this dependence is explored further. In particular, earlier work focused on nucleation and growth in the regime in which the second species is essentially immobile. This constraint is relaxed here, and the subsequent model studied through application of a self-consistent mean-field theory. Predictions for the total island density are presented.