It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field enhancement of several orders of magnitude. It is due to the excitation of quasistatic surface plasmon polaritons with particular small penetration depth in the metal. This may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such quasistatic plasmon polaritons in grain boundaries or notches of the films.

We investigate the optical response of two sub-wavelength grooves on a metallic screen, separated by a sub-wavelength distance. We show that the Fabry-Perot-like mode, already observed in onedimensional periodic gratings and known for a single slit, splits into two resonances in our system : a symmetrical mode with a small Q-factor, and an antisymmetric one which leads to a much stronger light enhancement. This behavior results from the near-field coupling of the grooves. Moreover, the use of a second incident wave allows to control the localization of the photons in the groove of our choice, depending on the phase difference between the two incident waves. The system exactly acts as a sub-wavelength optical switch operated from far-field.PACS numbers: 71.36+c,73.20.Mf,78.66.Bz Surface Enhancement Raman Scattering (SERS) still remains a mystery in a large part, even though it is now accepted that the excitation of localized electromagnetic modes of irregular metallic surfaces is involved in its basic mechanism [1,2]. Optical excitation of such modes can indeed lead to important concentration of electromagnetic energy in volumes (cavities) much smaller than λ 3 where λ is the excitation wavelength, as it is the case for SERS active surfaces. These specific places of very strong electromagnetic fields localization are called "active sites" or "hot spots". However, the debate on the origin of these hot spots remains open, as well as the hope to control one day this phenomenon. The large interest raised by this fundamental physics is also increased by its wide potential applications in biochips, sensors, nano-antennae, optoelectronics or energy transport on nanostructured surfaces.In this letter, we consider a simple system which allows to produce and control the localization in space of such hot spot phenomenon. It only consists of two deep grooves on a plane metallic gold surface ( fig.1). The excited modes appear, for the chosen geometry, in the infrared region where we can consider the metal as being a good reflector. Under this condition, a reliable theoretical method, i.e the modal method using surface impedance boundary conditions, can be used [3]. This method has already demonstrated its ability to give a good qualitative and quantitative agreement with the measured reflectivity of metallic gratings [4,5,6]. The case of one groove only was considered a long time ago [7], while the transmission for one [8] and two slits [9] were only recently considered. In contrast with [9], the distance between our two grooves is small with respect to the incident wavelength. Very recently it also was shown [10] that sharp and deep resonances appear in the transmission response of gratings with more than one slit per period or in gold dipole antennas [11]. We here analyze the physical origin of this new kind of resonances for a two slit system. As we will see, this allows us to point out some very fundamental aspects of electromagnetic resonances on metallic surfaces, and to control the light localization by using a simp...

We theoretically investigate an elementary subwavelength plasmonic sensor comprising a very thin active region. High quantum efficiency (QE), broad spectral band and nearly no sensitivity to the incidence angle and polarization can be achieved. We particularly discuss different examples based on HgCdTe for infrared detection: QEs of 75% are obtained for active layers λ/(8n) thin, corresponding to a tenfold absorption enhancement.

We provide the experimental and theoretical evidence that several nano-patch antennas assembled within a wavelength-scale region may constitute an efficient and easily tunable multi-band photodetector. The system uses highly confined localization states of light and exhibits a robust spectral sorting capability, paving the way to highly integrated hyperspectral imaging.

We study the light localization on commensurate arrangements of deep metallic sub-wavelength grooves. We theoretically show that as the degree of commensuration tends to an irrational number new light localization states are produced. These have properties close to that reported for hot spots on disordered surfaces and are not permitted for simple period gratings. Existence of these new resonances is experimentally provided in the infra-red region by reflectivity measurements performed on two commensurate samples with respectively two and three slits per period. Manipulations of these hot spots which can be controlled from far-field could be used for high sensitivity spectroscopy applications.

Ion implantation has the advantage of being a unidirectional doping technique. Unlike gaseous diffusion, this characteristic highlights strong possibilities to simplify solar cell process flows. The use of ion implantation doping for n-type PERT bifacial solar cells is a promising process, but mainly if it goes with a unique co-annealing step to activate both dopants and to grow a SiO 2 passivation layer. To develop this process and our SONIA cells, we studied the impact of the annealing temperature and that of the passivation layers on the electrical quality of the implanted B-emitter and P-BSF. A high annealing temperature (above 1000°C) was necessary to fully activate the boron atoms and to anneal the implantation damages. Low J 0BSF (BSF contribution to the saturation current density) of 180 fA/cm 2 was reached at this high temperature with the best SiO 2 passivation layer. An average efficiency of 19.7% was reached using this simplified process flow ("co-anneal process") on large area (239 cm 2 ) Cz solar cells. The efficiency was limited by a low FF, probably due to contaminations by metallization pastes. Improved performances were achieved in the case of a "separated anneals" process where the P-BSF is activated at a lower temperature range. An average efficiency of 20.2% was obtained in this case, with a 20.3% certified cell.

We report the study of a resonant bandpass filter made of a very thin subwavelength metal patch array coupled to a high index dielectric waveguide. The spectral properties of those filters can easily be tuned by playing on the lateral dimensions of the grating. They exhibit high and narrow transmission peaks together with very good rejection of light out of the pass-band and low angular dependance. An experimental demonstration using standard large scale silicon microelectronics processes is presented in the mid infrared spectral range. This concept of filters can easily be scaled throughout the optical spectrum, and can be integrated within focal plane arrays of various imaging technologies, down to visible wavelengths.

The use of ion implantation doping instead of the standard gaseous diffusion is a promising way to simplify the fabrication process of silicon solar cells. However, difficulties to form high-quality boron (B) implanted emitters are encountered when implantation doses suitable for the emitter formation are used. This is due to a more or less complete activation of Boron after thermal annealing. To have a better insight into the actual state of the B distributions, we analyze three different B emitters prepared on textured Si wafers: (1) a BCl 3 diffused emitter and two B implanted emitters (fixed dose) annealed at (2) 950°C and at (3) 1050°C (less than an hour). Our investigations are in particular based on atom probe tomography, a technique able to explore 3D atomic distribution inside a material at nanometer scale. Atom probe tomography is employed here to characterize B atomic distribution inside textured Si solar cell emitters and to quantify clustering of B atoms. Here, we show that implanted emitters annealed at 950°C present maximum clusters due to poor solubility at lower temperature and also highest emitter saturation current density (J 0e = 1000 fA/cm 2 ). Increasing the annealing temperature results in greatly improved J 0e (131 fA/cm 2 ) due to higher solubility and a consequently lower number of clusters. BCl 3 diffused emitters do not contain any B clusters and presented the best emitter quality. From our results, we conclude that clustering of B atoms is the main reason behind higher J 0e in the implanted boron emitters and hence degraded emitter quality.