Co-implantation: A simple way to grow doped Si nanocrystals embedded in SiO 2
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Co-implantation : A simple way to grow doped Si nanocrystals embedded in SiO2 Daniel Mathiot1, Rim Khelifi1, Dominique Muller1, and Sébastien Duguay2 1
Institut d'Électronique du Solide et des Systèmes (InESS, Université de Strasbourg and CNRS), 23 rue du Loess, B.P. 20, 67037 Strasbourg cedex 2, France. 2
GPM, Université et INSA de Rouen, UMR CNRS 6634, BP 12, Avenue de l’université, 76801 Saint Etienne du Rouvray, France. ABSTRACT Co-implantation, with overlapping implantation projected ranges, of Si and of the doping species (P, As, or B), followed by a single thermal anneal step, is proved to be a viable route to form doped Si-nc's embedded in SiO2, with diameters of a few nanometers. Extensive results of the evolution of the Si-nc's related photoluminescence, as a function of the dopant implanted dose, are presented and discussed. Atomic Probe Tomography (APT) is used to image directly the spatial distribution of the various species at the atomic scale. The 3D APT data demonstrate that n-type dopant atoms (P and As) are efficiently introduced in the "bulk" of the Sinanocrystals, whereas B atoms are preferentially located at their periphery, at the Si/SiO2 interface. INTRODUCTION For a couple of years, the optical and electronic properties of silicon nanocrystals (nc's) have been the subject of numerous studies because of their potential application in advanced electronic devices (e.g. nano-flash memories [1]), but also for advanced optoelectronic devices compatible with the Si technology [2], or even for the realization of next generation solar cells [3]. As usual for any (opto)electronic devices, depending on the exact application, the possibility to have an efficient doping technique of the nc's could be required. However, because of their large surface to bulk ratio, efficient doping of nc's is not trivial. In the case of phosphorus, as an example, recent theoretical results indicate that the dopant atoms are expected to be ejected to the surface when the nc size is below a critical value of a few nm [4]. From the experimental point of view, phosphorus- or boron-doped nc's have already been successfully achieved by high temperature phase separation from non-stoichiometric Si-oversaturated doped SiO2-x films deposited by various techniques [5-7]. It is also shown in [5] that the presence of the dopant atoms strongly affect the photoluminescence spectra of the nc's. Beside the method mentioned above, ion beam synthesis (Si implantation followed by thermal treatments) has been proved to be an efficient technique to form well-controlled Si nc's embedded in thermally grown SiO2 [8]. In the present study we show then that co-implantation of Si and of P, As or B is another efficient route to form doped nc's. The influence of the implantation dose on the photoluminescence (PL) spectra of the nc's is presented. In addition, thanks to a dedicated experiment using isotopic markers, the unambiguous determination of the exact localization of the dopant atoms is determined through a careful analysis of atomically resolv
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