Self-organized growth on GaAs surfaces

GaAs(001) has been one of the most intensively studied surfaces for the past 30 years due both to its importance as a substrate for epitaxial growth and to the challenge its phase diagram of complex structures presents to computational methods. Yet despite substantial experimental and theoretical effort, a number of fundamental questions remain concerning growth kinetics and mechanisms on this surface, even for homoepitaxy, but more especially in the formation of heterostructures. These issues have acquired a renewed timeliness because the quantum dots that are formed during the Stranski-Krastanov (SK) growth of InAs on GaAs(001) can be used for optoelectronic applications and have potential in quantum dot-based architectures for quantum computing. In this review we survey the current state of understanding of growth kinetics on GaAs surfaces, beginning with the simplest case, homoepitaxy on GaAs(001). We compare interpretations of recent reflection high energy electron diffraction measurements taken during the initial stages of growth with predictions of ab initio density functional calculations. We also consider the extent to which snapshot scanning tunnelling microscopy images from rapidly quenched samples truly reflect the growing surface structure as revealed by in situ real-time methods. We then examine the present experimental and theoretical status of the SK growth of InAs quantum dots on singular orientations of low-index GaAs surfaces, focussing on such issues as the importance of substrate orientation and surface reconstruction of the substrate, wetting layer formation, the nucleation kinetics of quantum dots, their size distributions and the role of strain. The systematics and anomalies of the phenomenology will be highlighted, as well as the current understanding of quantum dot formation. (C) 2004 Elsevier B.V. All rights reserved.