Self-assembly of quantum dots: effect of neighbor islands on the wetting in coherent Stranski-Krastanov growth

The wetting of the homogeneously strained wetting layer by dislocation-free three-dimensional islands belonging to an array has been studied. The array has been simulated as a chain of islands in 1+1 dimensions. It is found that the wetting depends on the density of the array, the size distribution and the shape of the neighbor islands. Implications for the self-assembly of quantum dots grown in the coherent Stranski-Krastanov mode are discussed.Comment: 4 pages, 6 figures, accepted version, minor change

Tight-binding study of the influence of the strain on the electronic properties of InAs/GaAs quantum dots

We present an atomistic investigation of the influence of strain on the electronic properties of quantum dots (QD's) within the empirical $s p^{3} s^{*}$ tight-binding (ETB) model with interactions up to 2nd nearest neighbors and spin-orbit coupling. Results for the model system of capped pyramid-shaped InAs QD's in GaAs, with supercells containing $10^{5}$ atoms are presented and compared with previous empirical pseudopotential results. The good agreement shows that ETB is a reliable alternative for an atomistic treatment. The strain is incorporated through the atomistic valence force field model. The ETB treatment allows for the effects of bond length and bond angle deviations from the ideal InAs and GaAs zincblende structure to be selectively removed from the electronic-structure calculation, giving quantitative information on the importance of strain effects on the bound state energies and on the physical origin of the spatial elongation of the wave functions. Effects of dot-dot coupling have also been examined to determine the relative weight of both strain field and wave function overlap.Comment: 22 pages, 7 figures, submitted to Phys. Rev. B (in press) In the latest version, added Figs. 3 and 4, modified Fig. 5, Tables I and II,.and added new reference

Self-organization of quantum-dot pairs by high-temperature droplet epitaxy

The spontaneously formation of epitaxial GaAs quantum-dot pairs was demonstrated on an AlGaAs surface using Ga droplets as a Ga nano-source. The dot pair formation was attributed to the anisotropy of surface diffusion during high-temperature droplet epitaxy

Optical Properties of GaAs Quantum Dots Fabricated by Filling of Self-Assembled Nanoholes

Experimental results of the local droplet etching technique for the self-assembled formation of nanoholes and quantum rings on semiconductor surfaces are discussed. Dependent on the sample design and the process parameters, filling of nanoholes in AlGaAs generates strain-free GaAs quantum dots with either broadband optical emission or sharp photoluminescence (PL) lines. Broadband emission is found for samples with completely filled flat holes, which have a very broad depth distribution. On the other hand, partly filling of deep holes yield highly uniform quantum dots with very sharp PL lines

Surface recombination, surface states and Fermi level pinning

Surface and interface recombination processes, which are becoming more and more important with the appearance of small-size optoelectronic devices, are still not well understood because reliable data are very scarce. We report here the first simultaneous in situ measurements of the density and position of surface states, of the position of the Fermi level at the surface, and of the surface recombination velocity, for various treatments of the surface of InP. Classical models are shown to describe correctly the relations between those quantities. A method for engineering (reducing) the surface recombination velocity in various situations by acting on the surface states is outlined, and applications to other semiconductors such as Si and GaAs are presented.Les processus de recombinaison aux surfaces et aux interfaces, dont l'importance croît avec l'apparition de dispositifs optoélectroniques de petite taille, ne sont pas encore bien compris, à cause du faible nombre de données expérimentales disponibles. On présente ici les premières mesures simultanées de la densité et de la position des états de surface, de la position du niveau de Fermi à la surface et de la vitesse de recombinaison de surface, pour divers traitements de la surface de InP. On montre que les modèles classiques décrivent correctement les relations entre ces quantités. On décrit une méthode pour moduler (réduire) la vitesse de recombinaison de surface en agissant sur les états de surface, avec des exemples d'applications à d'autres semiconducteurs comme Si ou GaAs

HOT ELECTRON EMISSION FROM SILICON UNDER PULSED LASER EXCITATION

Sous excitation modérée par un laser à impulsions, le silicium émet des électrons dans le vide à des énergies de photon bien en dessous du travail de sortie ϕ. Deux processus distincts sont observes : 1) une photoémission à deux quanta à de faibles flux de photon et à de fortes énergies de photon (> ϕ/2) et 2) une thermoémission à de forts flux de photon ou à de faibles énergies de photon ( ϕ/2) and, 2) a theormoemisssion at photon fluxes or low photon energies (< ϕ/2). While the first effect yields information about the electronic structure of silicon under irradiation, the second one probes the properties of the carrier plasma. The temperature of this plasma has been evaluated to (1800 ± 100) K for (0.04 Jcm-2, 2 ns) irradiances