T. Trifonov

Larger absolute photonic band gap in two-dimensional air–silicon structures

We investigate different aspects of the absolute photonic band gap (PBG) formation for two-dimensional photonic crystals, consisting of air rods drilled into silicon. Specifically, square lattices of square and circular rods are considered. The lattice symmetry, shape and orientation of the rods affect the photonic gap parameters. A symmetry reduction by addition of a smaller different shaped rod into the center of the lattice unit cell can produce significantly larger band gap. Combining the symmetry reduction and rotation of the noncircular rods yields the greatest improvements in the size of absolute band gap. We discuss the maximization of the absolute PBG width as a function of lattice parameters and the practical fabrication feasibility of these optimized structures.

Vertical hybrid microcavity based on a polymer layer sandwiched between porous silicon photonic crystals

A vertical hybrid microcavity is fabricated by sandwiching a polymer layer between distributed Bragg reflectors (DBRs) composed of porous silicon photonic crystals. The DBRs are made by electrochemical etching of Si and consist of alternating porous Si layers of high and low porosity, the top DBR being a freestanding film. The hybrid microcavity demonstrates a deep microcavity mode placed within a 200 nm wide photonic band gap, and reveals a many-fold enhancement of the third-order nonlinearity of the microcavity layer. The fabrication technique employed is rather simple, enabling the use of a variety of functional materials as the microcavity spacer.

Improving selective thermal emission properties of three-dimensional macroporous silicon through porosity tuning

We present a theoretical and experimental study on the effect of progressive porosity increase, through multiple oxidation/oxide removal steps, upon the optical characteristics in three-dimensional macroporous silicon. It is shown that, by increasing porosity, optical features can be pushed toward higher frequencies. Optimum porosities exist where normal or omnidirectional total reflection bandwidths are maximized, doubling the initial values. Results are confirmed experimentally through angle-resolved reflectance and thermal emission measurements.

“Silicon millefeuille” : From a silicon wafer to multiple thin crystalline films in a single step

During the last years, many techniques have been developed to obtain thin crystalline films from commercial silicon ingots. Large market applications are foreseen in the photovoltaic field, where important cost reductions are predicted, and also in advanced microelectronics technologies as three-dimensional integration, system on foil, or silicon interposers [Dross et al., Prog. Photovoltaics 20, 770-784 (2012); R. Brendel, Thin Film Crystalline Silicon Solar Cells (Wiley-VCH, Weinheim, Germany 2003); J. N. Burghartz, Ultra-Thin Chip Technology and Applications (Springer Science + Business Media, NY, USA, 2010)]. Existing methods produce “one at a time” silicon layers, once one thin film is obtained, the complete process is repeated to obtain the next layer. Here, we describe a technology that, from a single crystalline silicon wafer, produces a large number of crystalline films with controlled thickness in a single technological step.

Infrared thermal emission in macroporous silicon three-dimensional photonic crystals

In this paper we investigate the infrared thermal emission properties of macroporous silicon with modulated pore diameter. Samples with different pore modulation periodicities but fixed in-plane lattice constant are fabricated. Normal emission of these samples is measured between 373 and 673K. Room-temperature normal-incidence reflectance and transmission spectra are also measured and compared with the photonic band structure simulation. It is shown that thermal emission is suppressed due to photonic band gap effect along the pore axis in excellent agreement with the numerical calculations.

Thermal emission of macroporous silicon chirped photonic crystals

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.

Optical study of polymer infiltration into porous Si-based structures

This work describes the infiltration of a polymeric solution into porous Si structures towards the fabrication of tunable photonic crystals (PC) and microcavities for photonics applications. The tunability is achieved by infiltrating the porous silicon based PCs by active organic materials, such as an emissive and nonlinear polymer called 2-methoxy-5-(2- ethylhexyloxy)-p-phenylenevinylene (namely MEH-PPV). This preliminary work shows the infiltration of this polymeric solution into PC based on macroporous Si structure as well as in microcavities based on multiple layers of microporous Si. The solidification of the polymer was obtained by the evaporation of the solvent. Various techniques of infiltration were studied to obtain an optimized filling of the pores. The infiltration was then characterized using photoluminescence measurements. Finally, we will report on the study of third harmonic generation (THG) in samples of porous silicon microcavity infiltrated with MEHPPV. The k-domain THG spectroscopy was applied and an increase of the THG intensity up to an order of magnitude was achieved for the filled microcavity.

The Effect of Absorption Losses on the Optical Behaviour of Macroporous Silicon Photonic Crystal Selective Filters

The effect of losses in photonic crystal structures on transmittance and reflectance has been studied by numerical techniques, and compared to fabricated macroporous silicon samples. Material absorption and tolerances of the pores play an essential role in determining performance in optical applications. The relevance of the structure geometry has been investigated through the porosity. The considered photonic crystals in this paper are 3-d macroporous silicon structures fabricated by electrochemical etching with pore profile modulation, and defect inclusion. The examined structures are intended to work with quasi-normal light incidence as selective filters. The effect of losses on the forbidden band and resonance is studied and reported for both transmittance and reflectance. The reflectance peak is less affected by losses, while transmitted light experiences a noticeable reduction even for small absorption factors. This has critical implications for the performance of these structures as transmission filters. Furthermore, it is shown that an optimum can be found for a given absorption coefficient by choosing the appropriate porosity.

Macroporous silicon for spectroscopic CO2 detection

A carbon dioxide sensor based on a photonic crystal of macroporous silicon and measurements of its response are presented in this paper. Photonic crystals have opened new ways for the miniaturization of optical detector devices. In particular, macroporous silicon has proven to be a versatile material for many applications, and more specifically for the creation of photonic crystals in the MIR and NIR spectral regions. In this paper we present the design and fabrication of a MpSi photonic crystal with a photonic stopband in the lambda 4.2 μm region. This bandgap creates a spectral reflection peak centred on one of the main absorption bands for carbon dioxide which can be used to detect the presence of this gas. The device structure is a square lattice of modulated pores with a 700 nm pitch produced by electrochemical etching of silicon. No sensing materials such as polymers are used to perform detection, relying just on the spectral response of as-etched MpSi.

Synthesis of Ordered Polymer Micro and Nanostructures Via Porous Templates

The deposition of specific materials into ordered pores arranged in a regular lattice allows the fabrication of ordered fiber arrays. Polymer micro- and nanofibers using macroporous silicon and nanoporous alumina templates were fabricated employing a vacuum infiltration method for Poly(methyl methacrylate) (PMMA) structures or a melt-assisted template wetting into the pores for Poly(3-hexylthiophene) (P3HT) structures. We have studied how the aspect ratio of the micro- and nanopores and the kind of polymer influence the structures fabrication.