The InAs/GaAs(001) Quantum Dots Transition: Advances on Understanding

Abstract

In the heteroepitaxy of InAs/GaAs(001), the growing InAs layer remains planar up to a characteristic coverage (critical thickness) above which three-dimensional (3D) islands form. Such growth mode transition, conventionally called of the StranskiKrastanov (S-K) type, is the most distinctive aspect of the InAs/GaAs(001) system and is at the basis of the formation of self-assembled quantum dots, which are very attractive for optoelectronic applications. Although of the S-K type, such transition has a more complex evolution and a variety of fundamental process mediated by surface diffusion leads to interesting properties for this system, including scale invariance, which are worth to be studied from a basic point of view. Specific issues that will be addressed in this review are: i) the role of the composition of the InGaAs-alloy wetting layer (WL) at the transition [1, 2, 3]; ii) the sudden nucleation of 1010−1011 cm−2 coherent and partially relaxed QDs occurring within 0.2 ML of InAs deposition at the critical thickness for the 2Dto 3Dtransition; iii) the In-Ga intermixing in QDs; iv) the total nucleated 3D volume, far larger than that being deposited in the narrow coverage range where nucleation is completed. The interesting perspectives of QDs for optoelectronic devices, quantum computing and quantum cryptography have driven much attention on other important issues affecting the optical performance of self-assembled QDs. These are the homogeneity of their size and shape and the correlation of their lateral position on the surface. The fabrication of ordered arrays of dots by epitaxy, minimizing lithographic processes requires the capability to control at the nanoscale, microscopic processes involved in the 2D–3D transition. The issues listed above are among those lacking, at present, sufficient understanding with reference,in particular, to the dependence on substrate morphology, surface stress and kinetics of growth [4, 5, 6, 7]. Having in mind this research perspective, we report here the main results of our studies on the InAs/GaAs(001) heterostructure aiming at investigating the basic microscopic mechanisms driving the nucleation of QDs at each stage of their