Block Copolymer Templating for Formation of Quantum Dots and Lattice-Mismatched Semiconductor Structures
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1258-Q13-05
Block Copolymer Templating for Formation of Quantum Dots and Lattice-Mismatched Semiconductor Structures
S. Jha,1 C.-C. Liu,2 J. H. Park,5 M. K. Wiedmann,2 T. S. Kuan,3 S. E. Babcock,4 L. J. Mawst,5 P. F. Nealey,2 and T. F. Kuech2 1
Department of Chemistry Department of Chemical and Biological Engineering 4 Department of Materials Science and Engineering 5 Department of Electrical and Computer Engineering University of Wisconsin-Madison, Madison, WI 53706-1691, U.S.A. 2
3
Department of Physics University at Albany, SUNY, Albany, NY 12222, U.S.A.
ABSTRACT Templated growth for the fabrication of semiconductor nanostructures such as quantum dots and lattice-mismatched structures has been employed in this study. Self assembly of block copolymers (BCP) has been exploited to create a regular array of nanoscale patterns on a substrate to generate the growth template. These patterned templates were used for the selective area growth of pseudomorphic quantum dots, allowing for precise control over the dot size and spatial distribution. Strain relaxation in lattice-mismatched structures grown past the pseudomorphic limit was also studied. Analysis of the grown structures suggests that this approach using block copolymer templating followed by selective growth can be used for defect reduction in lattice-mismatched materials.
INTRODUCTION The development of approaches to integrate lattice-mismatched systems and formation of semiconductor nanostructures with uniform size and spatial ordering is essential for applications over a wide range of novel optoelectronic devices. Prepatterned substrates have been used in the past for the selective growth of nanostructures, such as quantum dots (QDs) [1-3]. This technique for QD fabrication allows for uniformity in QD size and density and eliminates the wetting layer that inevitably forms during self-assembled Stranski-Krastanov (SK) growth. This self assembly process, which is a consequence of the lattice- mismatch-induced strain, can be applied to QD fabrication only in systems with a large lattice mismatch. Quantum dots (lattice mismatched) grown past the pseudomorphic limit will strain relax in a prelude to the eventual large-area integration of lattice-mismatched materials. Reduced defect densities in the bulk of the subsequently grown film require the introduction of strain-relieving dislocations at the early stages of growth. Patterning followed by selective growth of small islands allows for such early
introduction of defects and hence development of strain-relaxed islands. Further growth of material takes place on these fully, or nearly fully, relaxed islands resulting in films with a reduced density of defects. In this study, we have employed BCP templating combined with selective growth for the formation of pseudomorphic quantum dot structures as well as structures beyond the pseudomorphic limit to gauge the impact of nanopatterning on the eventual strain relaxation of such structures. A cylinder-forming diblock copolymer, polystyrene-blockpolymethylmethacr
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