Transformations in endotaxial element and epitaxial III-V

compound semiconductor quantum dots

Peter Möck

Portland State University

P.O. Box 751, Portland, Oregon 97207-0751, USA

pmoeck@pdx.edu

 

This review consists of three parts. The first part gives a brief introduction to endotaxially and epitaxially self-assembled semiconductor quantum dots.

The second part of this review deals with endotaxially grown α-Sn (grey tin) quantum dots in Si matrix. The thermodynamics of small misfitting precipitates provide reasonable explanations for structural 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. Simple estimates show that an excess Gibbs free energy of several hundred meV per atom, corresponding to hydrostatic pressures on the order of 10 GPa, can be released by structural transitions from quantum dots with diamond structure to precipitates with β-Sn (white tin) structure and lattice mismatch strain minimizing orientation relationships with the surrounding Si matrix.

The third 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 in some numerical detail. 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.