Ángel Rodríguez Martínez

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.

Electrochemical Etching of silicon with sub-500 nm feature size

In this work we present the first steps towards achieving Photonic Crystals (PCs) operating in the Near-Infrared (NIR) wavelength range using Macroporous Silicon (MPS). The MPS structures herein shown are fabricated using Electrochemical Etching (EE) of silicon. Pores are arranged in a square lattice of 500 nm periodicity and pore size is around 200 nm to 350 nm. Preliminary results show straight pores with good uniformity and controlled dimensions.

Transmission and Thermal Emission in the NO2 and CO Absorption Lines using Macroporous Silicon Photonic Crystals with 700 Nm Pitch

Macroporous silicon photonic crystals with a cavity in the middle of their structure have been studied in both, transmission and emission. The initial transmittance of the photonic crystals was increased form 4%6% up to the value of 25%-30% by performing a rear attach of the samples of approximately 160 μm. The use of wafers with 700 nm of pitch allowed us to fabricate the optical response of the photonic crystals in the ranges of 6.4 μm and 4.6 μm, where different gases have their absorption frequency –such as NO2 or CO. The fabricated samples have been also heated in order to evaluate their viability to be used as selective emitters for gas sensing purposes. Results show a good agreement in the position of the respective peak compared to the transmission spectrum. However, further studies have to be done to place the base of the peak as close as possible to the 0% of emission in order to have a better selective emitter. This work is a starting point for gas detection devices using macroporous technology in the mid-infrared, which includes ammonia, formaldehyde, carbon monoxide or nitrous oxide, among others.

Macroporous Silicon: Technology and Applications

The knowledge of fundamental silicon questions and all aspects of silicon technology gives the possibility of improvement to both initial silicon material and devices on silicon basis. The articles for this book have been contributed by the much respected researchers in this area and cover the most recent developments and applications of silicon technology and some fundamental questions. This book provides the latest research developments in important aspects of silicon including nanoclusters, solar silicon, porous silicon, some technological processes, and silicon devices and also fundamental question about silicon structural perfection. This book is of interest both to fundamental research and to practicing scientists and also will be useful to all engineers and students in industry and academia.

Infrared thermal emission inmacroporous silicon three-dimensional photonics 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 673 K. 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.