PV Metamaterial Based on the Nanostructured Si
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1210-Q07-11
PV Metamaterial Based on Nanostructured Si Zbigniew T. Kuznicki, Patrick Meyrueis Photonic Systems Laboratory, Pôle API Parc d’Innovation, Boulevard Sébastien Brant, BP 10413, 67400 Illkirch, France ABSTRACT There are several ways to nanostructure Si. Some of them, e.g. nanoscale Si-layerd systems buried within the n+ layer of a crystalline Si can provide an initial material with unpredicted optoelectronic behavior. Such a transformation leads to a PV Si metamaterial, whose optoelectronic properties arise from qualitatively new response functions that are (i) not observed in the constituent materials and (ii) result from the inclusion of artificially fabricated, intrinsic and extrinsic, low-dimensional components. We show that an extremely strong c-Si:P absorptance, is larger than can result from conventional conversion because the surface population increases by injection of additional carriers from a nanostratum (transformed up to a Si-metamaterial) lying just behind the top c-Si:P-layer. INTRODUCTION Metamaterials are a new class of ordered structures that exhibit exceptional properties not readily observed in untreated materials. One proposed way is to use a nanostructurization [1], which can lead to a large modulation of the free-carrier density. The so-called free carrier dispersion [1-2], due to carrier photogeneration or injection, seems to be particularly useful in allsilicon solution for optical modulators in the place of the Franz–Keldysh, Kerr and Pockels effects, which are negligible or even inexistent in silicon. For low-energy photons a pronounced nonlinearity appears with an extremely large incident beam intensity (1027 photons cm-2s-1) because of impact ionization in the PN space charge region [3]. In the visible, additional carriers appear under much lower illuminations (1017 photons cm-2s-1) due to interband transitions. The densest steady-state electron gas (2.3x1021 cm-3) from P-doping, corresponding to Drude metallike densities, and modifying noticeably the refractive index in the 1.1-2.5 eV band, has been obtained by ion implantation and suitable laser treatment [4]. We have conceived a simple experiment to produce even larger free-carrier densities in crystalline Si (c-Si) due to optical excitations in the visible and UV, using relatively weak light beams (1014 - 1017 photon cm-2 s-1). The absorptance of a surface potential well (delimited by the buried nanoscale Si-layered system) indicates that the density surpasses largely 1022 cm-3. What is unusual, this density is inversely dependent on the potential well thickness. The origin of new performance can be localized in a buried Si-metamaterial nanolayer [5, 6] which determine the overall optoelectronic behavior of the device. EXPERIMENT Samples and their characterization A series of test samples, with a continuous nanoscale Si-layered system, was fabricated by double P-ion-beam implantation (140-220 keV and 15 keV) into c-Si wafers, moderately doped with B (about 5x1015 cm-3) and followed by adequate thermal treatment [5]. The p
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