Epitaxial and endotaxial semiconductor quantum dots: atomic order, morphological transformations, and structural transitions

Abstract

This updated review consists of three parts. The first part gives an introduction to epitaxially and endotaxially self-assembled semiconductor quantum dots. The second part of this review deals with both epitaxially grown (In,Ga)Sb compound semiconductor quantum dots in GaSb matrix and epitaxially grown In(As,Sb) compound semiconductor quantum dots in InAs matrix. These quantum dots are grown in the Stranski-Krastanow growth mode, are compressively strained to several percent and initially possess the sphalerite structure with the mixed cations and anions more or less randomly distributed over their respective sublattices. Experimental evidence for the existence of long-range atomic order within such III-V compound semiconductors quantum dots is reviewed. Employing the thermodynamics of small misfitting precipitates, a simple calculation for a model III-V compound semiconductor quantum dot system is given. This calculation demonstrates the possibility of structural transitions from ordinarily strained random semiconductor alloy quantum dots (with the sphalerite structure) to long-range atomically ordered quantum dots (i.e. crystallographic superlattices) that are negligibly strained because they possess lattice mismatch strain minimizing orientation relationships with the surrounding matrix. The third part of this review deals with endotaxially grown α-Sn (grey tin) quantum dots in Si matrix. Both the phase separation formation mechanism and the void-mediated formation mechanism of these entities are briefly discussed. The thermodynamics of small misfitting precipitates provide reasonable explanations for structural transitions and morphological transformations of such quantum dots. Morphological transformations within the diamond structure with the precipitate size are explained by an increasing contribution of the elastic mismatch strain energy to the Gibbs free energy.