Porous single crystalline 4H silicon carbide rugate mirrors

Revista Mexicana de Física, 2018

There are two main physical properties needed to fabricate 1D photonic structures and form perfect photonic bandgaps: the quality of thethickness periodicity and the refractive index of their components. Porous silicon (PS) is a nano-structured material widely used to prepare 1Dphotonic crystals due to the ease of tuning its porosity and its refractive index by changing the fabrication conditions. Since the morphologyof PS changes with porosity, the determination of PS’s refractive index is no easy task. To find the optical properties of PS we can usedifferent effective medium approximations (EMA). In this work we propose a method to evaluate the performance of the refractive index ofPS layers to build photonic Bragg reflectors. Through a quality factor we measure the agreement between theory and experiment and thereinpropose a simple procedure to determine the usability of the refractive indices. We test the obtained refractive indices in more complicatedstructures, such as a broad...

2017

Porous Silicon (PSi) samples with (100) orientation n-type were prepared by photo-electrochemical etching process for different variable parameters and fixed electrolyte solution HF:C2H5OH:H2O (2:3:3). Physical and optical properties of PSi would be varied with the variation of process parameters such as current density, anodization time and laser wavelengths. Two types of 50 mW diode lasers were chosen, 473 nm Blue & 532 nm green at 20 mA/cm2 & 15 min etching time to assist the iodization process. The band gap of the fabricated layer has raised up to (2.9 eV) which is more than twice its original value for the c-Si (1.12 eV). Exploiting the obtained gap energy values, the refractive index of porous silicon layer was calculated depending upon Vandamme empirical relation. It was observed that the porosity is modifiable through etching conditions, which in turn makes refractive index also modifiable. Thus, the calculation depended on taking certain parameters as the current density ...

Engineering and Technology Journal

In this work photo-electrochemical etching was used to synthesize uniform and non-uniform macro porous silicon from n-type with orientation (100). Specimens were anodized in a sol of 25% HF: C2H2OH at 1:1 rate. Morphology and porosity of the samples were studied. Optical characteristics (reflection and photoluminescence) of PS samples by changing current density (10, 12, 14 and 16 mA/cm 2) for fixed etching time (8min) and power density (17mW/cm 2) by using red laser illumination wavelength (645nm) were investigated. Porous silicon samples imaged via scanning electron microscope (SEM), which showed the topography of silicon surface and pores distribution.

Optics Express, 2007

Bragg reflectors with widths down to 300 nm have been fabricated in porous silicon. This was achieved by irradiation of highlydoped p-type silicon with a focused beam of high-energy ions in a channeled alignment, in which the beam is aligned with a major crystallographic direction. The reflected colour is controllably tuned across the visible spectrum by varying the ion irradiated dose. The depth distribution of ion induced defects differs in channeled alignment compared to random beam alignment, resulting in the hole current during subsequent anodisation being more confined to narrower lateral regions, enabling different reflective wavelengths to be patterned on a sub-micron lateral scale. This work provides a means of producing high-density arrays of micron-size reflective colour pixels for uses in high-definition displays, and selectively tuning the wavelengths of porous silicon Fabry-Perot microcavities across the visible and infra-red ranges for optical communications and computing applications.

International Journal of Nanotechnology, 2011

Electrochemical etching-a usual technique in nanotechnology-creates porous silicon with novel and useful properties. The considerable and controllable changes in the electronic structure and refractive index of porous silicon make it a promising material for photonics in comparison with bulk silicon. In this paper, we review as well as report on some interesting and unique properties of porous silicon material. In studying porous silicon as a low-dimensional material, we focus on the effect of the surface passivation of silicon nanocrystals on photoluminescence characteristics of such zero-dimensional crystals. As an optical material, we demonstrate the fabrication method and optical properties of the planar waveguide as well as the active waveguide and optical interference filters operated in infrared wavelengths. In addition, we investigated the effect of energy transfer from silicon nanocrystals to erbium ions in the erbium-doped porous silicon waveguide and also elaborate on the origins of the difference between the reflectivity spectra from fabricated filters and that of the simulation program.

physica status solidi (a), 2003

The sensitivity of the optical reflectivity of porous silicon structures to the refractive index of liquid within the pores is studied for a single layer, a Bragg mirror and a microcavity. Sucrose solutions of concentration in the range 0.05 to 1.0% by weight are introduced into the pores within a flow cell in order to change the refractive index of the liquid in the pores from 1.3330 to 1.3344. Optimum wavelengths for detection via reflectivity changes are determined based on a signal to noise analysis. The optical thickness of the single layer is also monitored by measuring the fringe spacing via a Fourier transform technique. It is just possible to detect the effect of a change in refractive index of liquid in the pores of 0.00007 for both the reflectivity and optical thickness approaches.

Applied Optics, 2005

We report an experimental study of porous silicon-based rugate filters. We performed filter apodization, following a half-apodization approach, which successfully attenuated the sidelobes at both sides of the photonic stop band. We achieved successful reduction of interference ripples through the insertion of index-matching layers on the first and last interfaces. An apodized dielectric mirror and a rugate filter are compared: Appreciable differences in the harmonic presence and stop-band performance were observed and are commented on. Bandwidth control when index contrast is modified is also demonstrated. Finally, the possibility of combining different rugate filter designs to attain more complex responses is demonstrated by the achievement of a multi-stop-band filter. Numerical calculations for design optimization and comparison with experimental data are reported too.

The measurements and calculations of monolayer and multilayer reflectance, made of porous silicon films, have been carried out. The multilayer component has been made of porous silicon layers that has refractive indices of n A =2.16 and n B = 1.55. The band structure of one dimensional photonic crystal has been calculated using the transfer matrix method which consists of alternative layers of two dielectric materials A and B. As for the multi layers component which are consist of the periodical repetition of two layers of different refractive indices (n H and n L) which has an omnidirectional photonic band gap (PBG), the width of which depends on the incidence medium and on the refractive index ratio n H /n L . In porous silicon, this ratio is limited by the material and fabrication characteristics. Theoretical and experimental study has been carried on the wide range of practical fabrication parameters for the formation of omnidirectional PBG. A band width of 400 nm is correspondi...

RSC Advances, 2016

Metal-assisted chemical etching was exploited for fabricating a porous silicon double beam interferometer composed of pillars with large pores on top of a monolayer with smaller pores which can act as a sensing and reference channel, respectively.

Advances in Chemical Sensors, 2012

The area of chemical sensors is one of the fastest growing both in research and in commercial fields. Most of the research work in this area is concentrated towards reducing the size of sensors and the identification and quantification of multiple species. Quick response, minimum hardware requirement, good reversibility, sensitivity, and selectivity are expected from an excellent sensor, and hence there is a need for further research. The applications of chemical sensors include quality and process control, biomedical analysis, medical diagnostics, environmental pollution control, continuous and long term monitoring of pollutants and hazardous substances. There are however several outstanding problems hindering applications of chemical sensors based on optical readout. It is widely accepted that in many instances the sensitivity is not the limitation of the sensor. Indeed many sensors display over-sensitivity at the expense of specificity and are vulnerable to noise. In real applications the environment in which sensors are located is not sterile: additional substances present will cause spurious readouts, and moreover, the substances may react over the sensor's surface and readouts will be then cross-correlated. Methods to overcome these hindrances are addressed in this chapter using porous silicon as a testbed. They are based on signal or statistical analyses of the data acquired and take advantage of the possibility of multi-sensing with properly modified sensor arrays. Several new configurations for optical multi-sensing are presented in this chapter, and demonstrated for ammonia detection. The methods are however generic for optical remote sensing of multiple gas components and can be applied to industrial and environmental gas supervision as well as biomedical applications. The detection of ammonia is based on chemical reaction between ammonia-sensitive dye and the detected molecules. These reactions are accompanied by changes in optical absorption spectrum within the VIS-NIR range. pH sensitive dyes have been widely used for ammonia detection . For these sensors, the response to ammonia vapour is highly dependent upon the level of humidity in the environment since the acid-base reaction of the dye materials is always mediated by water, and therefore calibrating for atmospheric humidity is required for determining true values of ammonia concentration. Advances in Chemical Sensors 48 Porous silicon (PSi) is typically produced by electrochemical etching of bulk crystalline silicon. The porosity of the produced material is directly proportional to the applied current density during the etching process, providing therefore a simple means to control its refractive index . Various optical components such as Bragg and rugate reflectors have been successfully fabricated with porous silicon . PSi can be used as smart transducer material in sensing applications, and in particular in the detection of vapours . Upon exposure to chemical substances, several physical quantities, such as refractive index, photoluminescence, and electrical conductivity change drastically. A key feature of a physical transducer, being sensitive to chemical molecules, either in vapour and liquid state, is a high surface area to volume ratio. Moreover, PSi is an available, low cost material, compatible with standard microelectronics processes, so that it can be successfully employed in the realization of smart sensors and microsystems.