Nalini et al. Nanoscale Research Letters 2011, 6:156 http://www.nanoscalereslett.com/content/6/1/156 N A N O E X P R E S S Open Access New Si-based multilayers for solar cell applications R. Pratibha Nalini, Christian Dufour, Julien Cardin, Fabrice Gourbilleau* Abstract In this article, we have fabricated and studied a new multilayer structure Si-SiO2/SiNx by reactive magnetron sputtering. The comparison between SiO2 and SiNx host matrices in the optical properties of the multilayers is detailed. Structural analysis was made on the multilayer structures using Fourier transform infrared spectroscopy. The effect of specific annealing treatments on the optical properties is studied and we report a higher visible luminescence with a control over the thermal budget when SiO2 is replaced by the SiNx matrix. The latter seems to be a potential candidate to replace the most sought SiO2 host matrix. Introduction The third generation of solar cells aims at reducing the cost and at improving the efficiency. Thin film solar cells based on silicon nanostructures is one of the most researched system to achieve such a target [1-3]. Ever since the discovery of the visible luminescence of the porous Si by Canham [4] various research groups have exploited the room temperature photoluminescent nat- ure of silicon by fabricating different kinds of Si-based nanostructures. The luminescence is attributed to the quantum confinement of carrier in Si-nanoclusters (Si- nc) [5-8]. Among the methods of obtaining the Si nanostructures we cite electrochemical etching [4,9], fabrication of silicon dots by plasma sputtering techni- que [10], and multilayer approach [8,11,12]. The important part of the ongoing research involves Si-nc embedded in an amorphous matrix such as SiO2, SiNx, or amorphous silicon. Though Si-nc embedded in SiO2 is the most common structure, the problem of car- rier injection in this matrix comes as a major drawback owing to the large band gap of SiO2. Hence the replace- ment of SiO2 by other dielectric matrices with smaller bandgap turns out to be a solution. SiNx matrix meets up these requirements and hence Si-nc embedded in SiNx matrix has become a material of choice in the recent past. In this article, we develop a new multilayer composition silicon-rich silicon oxide (SRSO)/SiNx to overcome the insulating nature of SiO2 by taking advan- tage of the reduced bandgap in SiNx. Using SiNx as the host matrix favors the electrical conductivity of carriers * Correspondence: fabrice.gourbilleau@ensicaen.fr CIMAP UMR CNRS/CEA/ENSICAEN/UCBN, 6 Bd. Maréchal Juin, 14050 Caen Cedex 4, France while we still maintain the quantum confinement as done with the SiO2 matrix. This study aims at fabricat- ing and comparing the light emission properties of three different kinds of multilayer compositions: (a) SRSO/ SiO2, (b) SRSO/SiNx, (c) SiNx/SiO2. Such a study is important to understand the influence of host matrices on the Si-nc and consequently to achieve an optimized solar cell device in the future. Experimental details Three kinds of multilayer structures were fabricated on 2” Si wafer by reactive magnetron sputtering comprising 50 patterns of SRSO/SiO2, SRSO/SiNx, and SiNx/SiO2. We define the gas flow rate as rg = fg/(fg + fAr) where fg represents the N or H2 gas flow and fAr represents the Argon gas flow. The SiO2 sublayer was fabricated by sputtering the SiO2 cathode under pure Ar plasma. Reactive magnetron sputtering, an approach developed by our team, was used for the fabrication of SRSO sub- layers. It takes advantage of the oxygen reducing capa- city of hydrogen when introduced into the Ar plasma [8]. The hydrogen-rich plasma favors Si excess in the SiO2 sublayer. Besides this in order to facilitate a higher incorporation of Si in the matrix, both SiO2 and Si cath- odes were used to fabricate the SRSO sublayer. The powers of SiO2 and Si were maintained as 7.4 and 2.2 W/cm2, respectively. The hydrogen rate rH was main- tained at 50% while the total flow fg + fAr was fixed at 10 sccm. The pressure in the chamber was chosen as 3 mTorr. Thus the SRSO/SiO2 multilayer structure was deposited by an alternative reactive sputtering under hydrogen-rich plasma for the SRSO layer and pure Ar plasma for the SiO2 sublayer. The SiNx layer was © 2011 Nalini et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.