Superfluorescence of Ion Beam Synthesized Dense-Packed Embedded CdSe Nanoclusters
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Superfluorescence of Ion Beam Synthesized Dense-Packed Embedded CdSe Nanoclusters H. Karl, I. Großhans, P. Huber and B. Stritzker, Institut für Physik, Universität Augsburg, D86135 Augsburg, Germany Dense-packed embedded semiconductor quantum dot (QD) layers with a multimodal size distribution are representing new types of QD solids. Their optical and electronic properties are modified due to dipole-dipole interactions and tunneling effects. In this work sequential high dose ion implantation of Cd and Se and subsequent thermal treatment is used to synthesize QD assemblies with the required structural properties in the surface near region of 500 nm thick thermally grown SiO2 on Silicon. We used cw photoluminescence (PL) to study PL-yield as a function of pump laser power at low temperatures for different various stoichiometries and annealing conditions. In these embedded QD assemblies of mixed size distribution we detected a promising non-linear increase of the PL-intensity with laser excitation power. The exponents evaluated are maximal for implanted Cd:Se-dose ratios between 0.8 and 1.0. The power law dependence of the PL-yield on pump laser power will be discussed in context with electronic energy transfer between dense-packed QD´s of different size, implanted dose ratios and postimplantation thermal treatment conditions.
INTRODUCTION Semiconductor quantum dots possess a broad variety of optoelectronic properties, which can be controlled by their size, their interaction, shape and surface structure. More especially, when QD´s are assembled in close proximity and are forming dense-packed QD solids they interact with each other. This leads to a delocalization of the localized electron states in single QD´s leading to next neighbor and even long range energy transfer[1]. Often a reduction of nonradiative loss [2] and a red shift of the optical transitions [3] can be observed. On the basis of the tunable interplay of the size-dependent properties of nanocrystals and the collective physical phenomena of the QD ensemble important applications like integrateable QD lasers, tunneling devices, planar waveguide amplifiers and efficient micro-LEDs may result, to name but a few. In nearly all of these applications high energy densities are involved, a typical issue of highly integrated miniaturized device architectures. This requires the use of chemically and physically stable materials for both the host materials and QD´s. Various synthesis techniques have already been developed to produce isolated and embedded semiconductor QD´s, but for achieving thin film QD solids in which collective phenomena can be observed only few of these techniques are suitable. One of them, the chemical synthesis route allows to produce QD´s with a very small size distribution. They can be assembled in a separate process into thin films of dense-packed QD´s. The stabilization is achieved by surface treatment of the QD surfaces prior to deposition from solution [4,5,6]. Another technique to synthesize semiconductor nanocrystals is ion impl
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