Pulsed Laser Deposition of Silicon Nanostructures
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Pulsed Laser Deposition of Silicon Nanostructures P. Bruno1, T. Salve2, V. Russo2, D. Dellasega2, G. Filoni2, C.S. Casari1,2, C.E. Bottani1,2, A. Li Bassi1,2 1
Center for Nano Science and Technology – IIT@PoliMI, via Pascoli 70/3, 20133 Milano, Italy.
2
Dipartimento di Energia and NEMAS – Center for NanoEngineered MAterials and Surfaces,
Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy.
ABSTRACT Silicon nanostructures embedded in an amorphous matrix have been synthesized by Pulsed Laser Deposition (PLD) at room temperature. The structural and optical properties of the materials were tailored by varying deposition parameters; attention has been devoted to the nanoscale morphology of the Si layers which has been varied from compact to open-porous by changing background gas (Ar) pressure (1-100 Pa). An adopted simple-minded strategy of a compact Si layer deposited on top of nanostructured layers showed to reduce quite successfully ex-situ oxidation. Raman spectroscopy suggests that as deposited samples are mainly constituted by amorphous silicon with nanocrystals (NCs) inclusions. The results indicate that the average size of the Si NCs varies in the range 2-6 nm. Photoluminescence (PL) responses are found to be strictly dependent on morphology and strengthen up the idea of the quantum confinement effect in the obtained nanostructured material. The results are interpreted in terms of particle size distribution, crystallinity and partial surface oxidation of the silicon nanostructures. INTRODUCTION In recent years quantum dot based solar cells have drawn a lot of attention because they essentially offer band gap engineering or multiple band-gap equivalence through the use of quantum dots embedded in a p-i-n junction or in a p-n one, lately leading to an increase in the device efficiency. Nanostructured Si would offer a suitable material for this kind of applications due to its unique properties; moreover the discovery of photoluminescence (PL) in the visible spectral region of nanocrystalline silicon at room temperature motivated the interest for investigations of light emission properties of different kinds of silicon based nanostructures (e.g. porous Si and surface oxidized Si NCs) [1-3]; however, the mechanism of visible PL is not clear and is still controversial. Porous silicon, nanocrystalline silicon in SiOx matrix and several other types of nanostructured silicon including Si quantum dots have been synthesized using different techniques such as Plasma Chemical Vapour Deposition (P-CVD) [4], Hot Wire Chemical Vapour Deposition (HW-CVD) [5], RF co-sputtering deposition [6] and by chemical routes [7]. Pulsed Laser Deposition (PLD) in a background gas is a method for fabricating nanoparticles and nanostructured materials with very high purity [8-9] even at room temperature thus allowing deposition on temperature sensitive substrates like plastics. The possibilities offered by PLD for the synthesis of Si nanostructures using inert and reactive gases can be found elsewhere [10-12];
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