Synthesis and Screening of Materials Libraries of Buried Compound Semiconductors by Ion Beam Implantation
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Synthesis and Screening of Materials Libraries of Buried Compound Semiconductors by Ion Beam Implantation I. Großhans, H. Karl and B. Stritzker Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany ABSTRACT A combinatorial approach was employed to ion beam synthesis and optical analysis of buried II-VI compound CdSe semiconductor nanocrystals. Typically standard ion implantation setups are designed in a way to create a laterally homogenous dose distribution of the implanted ion species. In order to achieve intentional lateral variations of the implanted doses a special implanter endstation was constructed. Computer controlled apertures in front of the wafer cover up in succession parts of a 4 in. wafer, so that a lateral pattern of distinct dose combinations of the implanted elements Cd and Se was generated. The obtained materials library consists of 1:1 stoichiometric, but also off-stoichiometric dose ratios. After implantation the wafers passed through a rapid thermal heat treatment, where the implanted material forms buried semiconductor nanocrystals. Photoluminescence spectra of the elements of the materials library were screened in rapid succession in an optical cryostat into which the whole wafer was mounted and cooled down. The obtained spectra were compared and key-parameters determined which control the photoluminescence properties. In this contribution will be shown, that slight variations of the dose ratio significantly alter the optical properties and that new efficient photoluminescent materials and processing parameters can be found. In this way, also other complex interdependencies of physical and chemical parameters in the field of multiple element ion beam implantation might be efficiently investigated.
INTRODUCTION Currently semiconductor nanocrystals (quantum dots) are attracting remarkable interest on account of their unique optical and electrical properties. Due to the 3-dimensional confinement of the carriers the quantum size effect is most pronounced in quantum dots. This spatial confinement leads to a molecular optical behaviour, which is both of fundamental and technological importance [1-2]. One technique to synthesize semiconductor nanocrystals is ion implantation followed or accompanied by heat treatment [3-4]. This technique deserves great attention, since it allows to embed quantum dots into standard semiconductor materials systems and thus to integrate heterogeneous functional materials into thin films for application in optoelectronic devices. In this article we concentrate on the classical example of an optically active direct bandgap semiconductor: CdSe. Its optical properties in and also close to the quantum confinement regime are modified by impurities, defects, surface states and also by the electronic and structural properties of the surrounding host material. Due to this interplay of different factors the complexity increases tremendously. The combinatorial synthesis and analysis approach is suitable to optimize and finally to support the understanding
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