Highly Ordered Uniform Quantum Dots Induced by Ion Sputtering
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H. Kurz, S. Facsko, T. Bobek, and T. Dekorsy Institute of Semiconductor Electronics, RWTH Aachen, Sommerfeldstr. 24, D-52056 Aachen, Germany
ABSTRACT
Self-organized hexagonally ordered quantum dot patterns are produced on GaSh (100) and InSb (100) surfaces by low energy Ar+-ion sputtering at normal angle of incidence. The QDs are crystalline, exhibiting narrow size distributions with diameters from 17 - 80 nm depending on sputter conditions, densely packed with densities as high as 2 x 1011 cm2 . The origin of the QD formation is attributed to the interplay of two surface processes during ion bombardment: ion induced surface roughening, provoked by the curvature dependent sputter yield and balanced by surface diffusive processes. The observed QD patterns obtained at different sputter conditions show that the formation mechanism can be described by the Kuramoto-Sivashinsky equation. The dominant diffusive process emerges to be effective ion induced without any mass transport on the surface, inherent to the sputtering process.
INTRODUCTION Semiconductor quantum dots (QDs) are expected to play a prominent role in future electronic and optoelectronic devices, like QD lasers [I], single electron transistors [2], or QD cellular automata [3]. Key requirements for their use are their size, size uniformity, density, alignment, and crystal structure. Although electron beam lithography meets the major demands for the production of QDs the low throughput due to the serial processing and the crystal defects generated by the etching process are great disadvantages of this direct patterning technique. Alternative methods for the parallel fabrication of large arrays of well defined QDs have been pursued extensively in the past based on self-organization mechanisms. For defect free QDs the Stranski-Krastanow growth has been used predominantly [4]. The high complexity of the molecular beam epitaxy (MBE) process involved, the rather large spread in their size distribution through thermal fluctuations, and the restricted possibilities for lateral ordering of these QDs hampers their potential in nanoelectronics. Other self-organization techniques have been presented, like electrochemical self-assembled QDs [5], diblock-copolymer mediated metal QDs [6], or deposition of uniform clusters. Recently, we presented a new route for the generation of QDs based on a self-organization mechanism on solid surfaces during the erosion of the solid by ion sputtering [7]. Under low energy normal incident ion bombardment a regular dot pattern appears spontaneously on initially flat GaSb (100) and InSb (100) surfaces. This method offers a self-organized subtractive process and is an attractive alternative to SK-growth. Ion sputtering is used extensively in semiconductor technology, for instance in ion etching, cleaning, or thin film deposition, and in analysis of solids and solid surfaces, i.e. mass spectrometry. Various morphologies are produced during the erosion by ion sputtering and are subject of intense research [8-10]. The appearance of period
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