Mechanically Biased Self-Assembly of Quantum Dots by Nanoindentation
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0921-T07-07
Mechanically Biased Self-Assembly of Quantum Dots by Nanoindentation Curtis R. Taylor1, Ajay Malshe2,3, Eric Stach4, Euclydes Marega5, and Gregory Salamo6 1 Mechanical Engineering, Virginia Commonwealth University, Richmond, Virginia, 232843015 2 Mechanical Engineering, University of Arkansas, Fayetteville, Arkansas, 72701 3 Microelectronics-photonics, University of Arkansas, Fayetteville, Arkansas, 72701 4 Materials Engineering, Purdue University, West Lafayette, Indiana, 47907 5 Physics, University of Sao Paulo, Sao Paulo, CEP 13560-970, Brazil 6 Physics, University of Arkansas, Fayetteville, Arkansas, 72701 ABSTRACT Nanoindentations were created in the GaAs(100) surface to act as strain centers to bias the nucleation of self-assembled InAs quantum dots providing for patterned growth. Indents were generated using loads below 450 µN with a sharp cube corner indenter. Growth of InAs quantum dots on indent patterns is performed using molecular beam epitaxy (MBE). The effect of indent spacing and size on the patterned growth is investigated. The structural analysis of the quantum dots including spatial ordering, size, and shape are characterized by ex-situ atomic force microscopy (AFM). Results reveal that the indent patterns clearly bias nucleation with dot structures selectively growing on top of each indent. It is speculated that the biased nucleation is due to a combination of favorable surface strain and multi-atomic step formation at the indent sites, which leads to increased adatom diffusion on the patterned area.
INTRODUCTION Strain-driven, self-assembled, three-dimensional quantum dots (QDs) randomly distributed over GaAs(100) surfaces have been an exciting area of research for the last decade. The random nature of nucleation during self-assembly, however, results in a non-uniform distribution of QD sizes and an inability to control their physical location for integration purposes. Future devices, such as lasers, require size uniformity to reach their potential in mechanical, electronic, and optical properties. Also, in order to integrate QDs with existing micro-devices, the structures must be able to be positioned and patterned at precise locations. Therefore, there exists a tremendous need for the development of simple, inexpensive, and robust techniques for patterned quantum dot arrays. We propose that nanoindentation by a nanoindenter may be a very promising technique for the patterning of QDs. This is because mechanical indentation by a nanoindenter can produce highly localized dislocations in crystalline materials. The elastic strain fields from dislocations have been used to produce remarkably selective patterning of Ge dots on Si and InAs dots on GaAs [1-4]. However, it is difficult to control the spatial nucleation of dislocations. Thus, nanoscale control of dislocation nucleation by nanoindentation would provide a highly effective patterning mechanism. Here we report on the growth of QDs by MBE on nanoindent patterned GaAs(100) templates.
EXPERIMENTAL DETAILS A TriboIndenter® (Hysitro
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