Semiconductor Nanostructures defined by self-organizing Polymers
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Semiconductor Nanostructures defined by self-organizing Polymers Michael Haupt1, Stephan Miller1, Andreas Ladenburger1, Rolf Sauer1, Klaus Thonke1, Silke Riethmueller2, Martin Moeller2, and Florian Banhart3 1 Abt. Halbleiterphysik (Dept. of Semiconductor), 2 Abt. Makromolekulare Chemie III (Dept. of Organic and Macromolecular Chemistry III), 3 Zentrale Einrichtung Elektronenmikroskopie (Dept. of Electron Microscopy) University Ulm, Albert-Einstein-Allee 45, 89069 Ulm, Germany
ABSTRACT In the near future it will be more and more important to produce real nanometer-sized structures for semiconductor devices (e.g., quantum dot lasers) but also for nano-biomechanical applications like the so-called “total analysis system” implemented on one chip. We describe here a technique to create nanometer-sized structures in semiconductors and metals by the use of self-assembling diblock copolymers as nano-lithographic masks. Semiconductor quantum structures with very high aspect ratio of 1:10 were fabricated from III-V semiconductor heterostructures by anisotropic dry etching. In a first step, so-called diblock copolymer micelles were generated in a toluene solution. These micelles were loaded by a noblemetal salt. With a “Langmuir Blodgett” technique we can decorate complete wafers with a monolayer of highly ordered micelles, covering almost the complete surface. After treatment in a hydrogen plasma all of the organic components are removed and only crystalline metal clusters of ≈12 nm size remain. This metal cluster mask can be used directly in a highly anisotropic chlorine dry etching process to etch cylinders in GaAs and its In and Al alloys. It is also possible to etch through a quantum well layer underneath the surface in order to produce quantum dots. By evaporating metals and applying a wet chemical image reversal process, we can invert the etched structure and generate a gauzy gold film with nano-holes inside. It is thinkable to use this porous gold film as a nano-filter in upcoming nano-biotechnology applications.
INTRODUCTION In the last few years advances in electron-beam, ion-beam and scanning probe lithography techniques have pushed the minimum size of micro-fabricated structures below the 50 nm scale. These techniques are powerful, but very expensive and time consuming, because they all work serially [1]. In contrast, the preparation of nanostructures, which takes advantage of selforganizing effects, is highly parallel and consequently fast and cheap [2]. In semiconductors, confinement effects become increasingly important with the decrease of the structure sizes. Especially quantum dots (QD) enjoy great attention because of possible device applications in lasers, detectors, optical filters, or single electron transistors. The established way to fabricate QDs is the self-organized growth of strained islands using the Stranski-Krastanov growth method [2,3] in molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition [4]. An alternative approach, which we report here, is the use of self-organizing pol
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