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Zinc oxide/silicon nanowires (ZnO/SiNWs) nanocomposites is a promising material for heterojunction solar cells. They combine the low-reflectivity of SiNWs, where photogenerated charge carriers are produced and harvested, and the high transparency of ZnO, which serves as a functional transparent conductive electrode. In this paper, we present a study of the anti-reflective properties of ZnO/SiNWs core-shell nanostructures. SiNWs were fabricated by a two-step metal-assisted chemical etching and coated with ZnO by electrochemical deposition. Particularly, the change in the specular reflectance of ZnO/SiNWs nanocomposites as a function of thermal annealing temperature under ambient atmosphere is investigated. First, it was shown that the reflectance in the wavelength range of 400-1000 nm of as-synthesized ZnO/SiNWs nanocomposites increases when compared to the bare SiNWs formed from Si wafers with resistivity of 0.3 and 12 Ω∙cm by an 0.51 % and 0.47 %, respectively. Second, it was found that annealed ZnO/SiNWs had a 0.26 % and 0.17 % lower reflectance in the wavelength range of 400-1000 nm than as-synthesized ZnO/SiNWs and yet higher than bare SiNWs. Potential causes such results are discussed in the context of existing literature.

[EN] A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, European Commission through the project H2020-644242 SAPHELY; Spanish government through the projects TEC2013-49987-EXP BIOGATE and TEC2015-63838-C3-1-R-OPTONANOSENS; Generalitat Valenciana through the Doctoral Scholarship GRISOLIAP/2014/109.

An electrochemical deposition process of ZnSe and CdSe compound semiconductors from aqueous acidic solutions onto silicon substrates with porous silicon layers formed on their surfaces was studied by the voltammetry method. The experimental data obtained were compared with the deposition data onto metal and silicon substrates, and the optimal conditions for the binary compound deposition onto porous silicon were determined. Semiconductor films deposited were studied by scanning electron microscopy, X-ray diffractometry, and X-ray microanalysis. The films are shown to have the crystalline structure and a nearly stoichiometric composition with a minor Se excess. Further annealing in air for 15 min allowed the Se concentration to be decreased.

We studied the influence of the thickness and porosity of the buffer layer on the guiding properties of oxidized porous silicon waveguides (OPSWG). It is demonstrated how a modified anodization process acts on the porosity of the final oxidized porous silicon. In this way, it is possible to control the refractive index jump between the core of OPSWG made of compact silicon dioxide and the bottom buffer layer made of porous silicon dioxide. The adoption of a double-step anodization process decreases the propagation losses to 0.5 dB / cm against the 8 dB / cm measured for the waveguide realized using a single-step anodization. The main reason seems not to be the increase of the difference of refractive index values but the more homogeneous buffer layer obtained along the core of the waveguide. This homogeneous layer permits a better lateral confinement of the light as demonstrated by spatial refractive index profile measurement.

Different types of silicon modified patterned substrates with and without p–n-junction were applied as a way for improving solar cells performance in order to prevent the light losses: (i) pyramid like (textured) surfaces (PrS); (ii) hemispherical plate like surface forms (PIS); (iii) dendritic structures (DS); (iv) porous morphology (LEPSi); (v) combinations of a textured surface with a porous one, etc. To realize them the anisotropical chemical and electrochemical etching in various etched mixtures and regimes, epitaxy and ion implantation were performed. Using scanning electron microscopy, spectral photoresponse measurements and current–voltage data, the morphological design, the variations in the photosensitivity, the wavelength peak position and the recombination parameters induced by the patterned processing and their influence for achieving the successful Si solar irradiance detection have been studied and analysed.

Magnetoresistance oscillations were observed on networks of superconducting ultrathin Nb nanowires presenting evidences of either thermal or quantum activated phase slips. The magnetic transport data, discussed in the framework of different scenarios, reveal that the system behaves coherently in the temperature range where the contribution of the fluctuations is important., accepted for publication on Nanotechnology

Low cost concept based on the porous silicon technology is shown to be well suitable for integrating monolithically the photonic devices on a standard silicon wafers by using localized SOI structures fabricated by electrochemical anodization of silicon wafers followed by thermal oxidation of porous silicon. The new approach consists in realizing buried localized porous oxidized silicon by exploiting two different routes: n - epi/n + /n - structures on p-type wafers and ion-implantation on standard CMOS/BiCMOS wafers. The peculiarities of the developed approach, including anodization and thermal oxidation regimes to form oxidized porous silicon regions with the required properties are presented. The advantages of the proposed approach in realizing the fiber-to-chip and power-over-fiber coupling are discussed.

In the present work, we report on the heteroepitaxial growth of PbS on porous silicon (PS). Epitaxial PbS films were grown by MBE on the surface of PS formed on the n+-type silicon (111) substrate. The films were comparable with films grown on BaF2 substrates. Beneficial influence of a PS buffer layer on the structure and properties of PbS epitaxial films was supported by implementation of sensitive Schottky-barrier photodiodes fabricated in these films.

The greatest limit in high-speed communications between different circuit blocks is due to the delays introduced by metal interconnections. Knock-down wire communication bottleneck is, therefore, one of the best goals that current research could reach in the field of fast electronics. A possible solution is to build fast optical links and even better if the technology is based on silicon. To attain these ends, we have made studies into possibility to fabricate optical waveguide based on oxidized porous silicon. In the last few years, such a device was realized and characterized. Waveguiding in the visible and in the near infrared was demonstrated, with propagation losses of about 3–5 dB/cm for a light with a wavelength of 632.8 nm. Moreover, a design feature of an integrated waveguide based on oxidized porous silicon is that it offers a spontaneous bending of the waveguiding layer at its ends. The edge bending is provided by a convex camber of a leading edge of forming porous silicon. This bending can be exploited to promote a vertical light output with no use of any additional devices. The paper discusses the properties of edge bending, evaluation of the light losses depending on the radius of curvature, and analysis of possibilities to reduce these losses.

A brief review of 20-years research of formation, processing and utilizing of oxidized porous silicon (OPS) is presented. Electrolytes to form porous silicon (PS) layers, special features of PS chemical cleaning and thermal oxidation are discussed. OPS application for dielectric isolation of components of bipolar ICs and for the formation of silicon-on-insulator structures has been demonstrated. Although these OPS-based techniques have found limited current commercial use, experience gained is applicable to the fabrication of optoelectronic devices. Specifically, integrated optical waveguides based on OPS have been developed.

Epitaxial PbS films were grown by molecular-beam epitaxy (MBE) on the surface of porous silicon (PS) formed on the silicon substrate of (111) orientation. The uniform PS layers 5 μm thick were produced by electrochemical anodic treatment of n + -silicon in HF solution. The structure of both PbS and buffer PS was studied by X-ray diffraction analysis as well as scanning electron microscopy. The PbS layer has been demonstrated to have a columnar structure at the early stages of growth, while a solid structure of the grown layer has been observed with increasing a thickness of the epitaxial layer up to 0.5–1.0 μm. PbS epitaxial films grown on the substrates with the 2–5 μm thick PS layers of 20–40% porosity were comparable with the films grown on the BaF 2 substrates.

A low-dimensional matrix of porous silicon (PS) was found to be an effective host material for erbium (Er) electrodeposition from Er(NO 3 ) 3 ·5H 2 O/ethanol solution. After thermal annealing at 850–1200 °C in an O 2 -containing atmosphere, such material exhibited sharp 1.54 μm luminescence at 77 K and 300 K. In contrast to previous studies, strong Er-related photoluminescence (PL) was found not only in the case of red-emitting PS formed in initial p-Si(111) wafers of 0.3 Ω cm resistivity but also for micro-sized material formed in initial 0.01 Ω cm n + -Si(111). Erbium doping of p-type PS resulted in a 1.54 μm peak appearance in addition to two broad PL bands at about 1.3 μm and 0.8–0.9 μm. In contrast, n + -type PS:Er exhibited only a sharp 1.54 μm peak without other PL bands. The intensity of the Er-related peak depended strongly on the Si anodization regime and increased with the PS thickness growth from 1 to 20 μm. Application aspects of PS:Er for light-emitting devices and integrated optical waveguides are discussed. © 1997 Elsevier Science S.A.

Porous-silicon-based white-light-emitting devices are presented. The fabrication process on different substrates is described. The peculiarities of technological steps for device fabrication (porous-silicon formation and aluminum treatment) are underlined. Doping profile of the porous layer, current-voltage characteristics, time response, lifetime tests and electroluminescence emission spectrum of the device are presented. A model for electrical behaviour of Al/porous silicon Schottky junction is presented. Electroluminescence spectrum of the presented devices showed strong similarities with white emission from crystalline silicon junctions in the breakdown region.

The electrical behaviour of electroluminescent Schottky diodes fabricated on the base of aluminum and n-type porous silicon is reported. Porous silicon was formed by electrochemical etching in HF aqueous solutions of n-type monocrystalline silicon and of degenerate n + -type polysilicon. The polysilicon layer was formed on monocrystalline silicon substrate by low pressure chemical vapour deposition (LPCVD). The electroluminescence (EL) starting voltage was in the range 4–20 Volt, depending on the doping level of Si substrate; polysilicon samples showed a higher starting voltage. Developed devices showed broad EL spectra, covering the whole visible range. Electrical measurements include current-voltage characteristics and capacitance-voltage characteristics. Time response and stability of the light emitting devices was also measured, showing excellent speed and reliability characteristics.

Porous silicon doped by erbium electrodeposition or from spin-on silica gel film followed by rapid thermal processing at 950 °C or higher exhibited liquid-nitrogen and room-temperature luminescence at 1.54 μm. The full width at half maximum was about 0.01 eV at 77 K. The mechanism of light emission from erbium-doped porous silicon is proposed. The direct bandgap of nanocrystallites in porous silicon is considered to provide an effective pumping media.

Optical waveguiding has been observed in oxidized porous silicon layers. Main steps of integrated optical waveguide formation and experimental results on lightguiding in the visible range are presented.

In this work it is described an high-density contacting technology that can replace wire bonding in power electronic applications, to overcome known limitation of bond wires liftoff occurring after several power cycles due to the difference in the coefficient of thermal expansion of silicon and aluminum. In the presented technology, MEMS (micro-electro-mechanics systems) micro-fabrication processes are used to realize contact structures that, pressed against the silicon dice, provide a reliable compliant contact. One advantage of this technology is that the contacts can be hosted on a printed circuit board that integrates the control circuitry for the power devices. This will reduce the footprint of power systems, like Integrated High Power Modules (IHPM). Reduced footprints are beneficial in applications where space is a concern, like the automotive industry. The description of the technological steps for building the contacting assembly is reported together with process conditions and electrical performances of two test structures.

The present work reports Er-doped channel oxidized porous silicon waveguides (OPSWG) formed from n + -type Si by the two-step anodisation process. Er has been introduced into porous silicon before oxidation by a cathodic treatment in 0.1 M Er (NO 3 ) 3 aqueous solution. A correlation between Er concentration and refractive index profiles has shown dominant core doping with Er relative to cladding regions. Reported Er concentration of 0.8 at.% in the OPSWG is large enough to attain the amplification effect.

Most power electronic modules are specifically designed for the customer and this entails intense labour during the production phase. The monolithic integration for power electronic devices in the form of power IC has not proven to be efficient, neither from a technical, nor from an economic point of view. In a typical high power module the power devices are assembled on a heatsink and, driver, sensor and protection circuits are mounted on separate PCBs assembled to the power devices. This results in low performance and high cost. Higher integrated power modules are produced assembling power devices in die format onto a DCB (Direct Copper Bonding) substrate and interconnect them by wire bonding technique [1]. The relative driver, sensor and protection circuits are surface mounted on a separate PCB assembled with the former.

Porous silicon (PS) prepared from n-type Si crystal is proposed as a new material for the fabrication of sensitive substrates for surface-enhanced Raman scattering (SERS). The formation procedure for nanostructured silver films on the surface of PS was optimized. Maximum of SERS enhancement for rhodamine 6G probing molecule is observed for samples obtained by the immersion plating from the water solution of AgNO 3 with the 10 mM concentration during 5 min. The dependence of morphological parameters of PS and corresponding silvered surfaces on the anodization current density has been studied. It is shown that the most SERS activities possess substrates produced from PS with lower porosity. The optimum of the PS layer thickness for high Raman signal is about 5 μm. The detection limit for rhodamine 6G adsorbed on Ag-coated PS from the 100 pM solution is established to be comparable with that for p-type PS-based substrates. Thus, the n-type porous silicon is suitable material for the preparation of sensitive SERS-active substrates.

Oxidised porous silicon optical waveguides (OPSWG) are fabricated and characterised. Porous silicon, selectively formed on boron-doped silicon substrates, is oxidised in order to obtain a channel SiO2 optical waveguide. Light confinement within the guide is obtained by a decreasing profile of the refractive index of the oxidised porous silicon from the centre of the guide toward the surrounding silicon. Light guiding is observed in the whole visible range. Out-of-plane scattering and near-field profile are measured. A Scanning Electron Microscopy (SEM) micrograph of the resulting waveguide is shown. OPSWG are promising as silicon technology optical links for optoelectronic interconnections in VLSI integrated circuits. © 1997 Elsevier Science S.A.

In the present work, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy were used to study oxidized porous silicon (OPS) doped with Er by electrochemical migration. Three types of OPS were investigated: (a) partially oxidized PS (POPS); (b) fully oxidized PS (FOPS); (c) oxidized PS co-doped with Fe (OPS:Fe). The OPS consists of oxide, Si nanoclusters and voids, and their composing fractions are dependent on the PS porosity and oxidation regime. The main result of this work is the assessment that the location of Er ions in composing fractions of OPS has a profound effect on the PL and PLE spectra. We show that for both POPS and FOPS, Er exhibits a broad 1530 nm PL spectrum similar to that observed in the Er-doped silica glasses. For POPS, the PLE spectrum of the 1530 nm Er PL band consists of a superposition of sharp peaks, which are attributed to the absorption transitions of Er ions incorporated into the oxide fraction, and a broad band, which is related to the absorption band of Si nanoclusters. For FOPS, the PLE spectrum consists just of sharp peaks. In contrast to POPS and FOPS, for OPS:Fe, Er PL spectrum consists of 21 highly resolved peaks. PLE spectrum of the strongest 1535 nm PL peak represents a wide band which is attributed to the absorption band of Fe:O nanoclusters formed inside OPS:Fe. Mechanism of excitation and luminescence of Er ions in OPS is presented.

In this work we report the latest improvements in integrated optical waveguides based on oxidized porous silicon. Remarkably low propagation loss of 0.2 dB/cm in the visible is demonstrated. Straight waveguides of 1–10 cm long were fabricated in N+-type silicon substrates. Thickness of core region of all fabricated waveguides was of 8 μm while thickness of cladding layer was of 0.8, 1.5, and 2.5 μm. Optical loss in the visible and IR were measured by original method utilizing the 90° vertical bending at the waveguides endings which is a unique property of our waveguides. Significant improvement of the waveguide characteristics was obtained by optimizing the technological process: (a) eliminating the negative effect of swirl defects on uniformity of porous silicon layers; (b) developing the anodization regimes allowing the careful control of the porosity through the porous silicon thickness; (c) using silica mask instead of silicon nitride mask.

The fabrication and the properties of light-emitting aluminum-porous silicon Schottky diodes, formed on the base of highly doped n-type polysilicon are presented. The polysilicon layer was formed on a crystalline silicon substrate by low-pressure chemical vapour deposition. Highly doped n+-poly-Si was then formed by phosphorous thermal diffusion. On this material the porous layer was obtained by electrochemical anodization using process parameters between electropolishing and pore formation regimes. The structure of the formed layer was investigated using the transmission electron microscopy technique. Photoluminescence spectra obtained after anodization are reported. The aluminum electrodes (pads) were obtained by standard photolithography and subsequent electrochemical aluminum anodization process. Electroluminescence (EL) was observed in reverse biased junctions. EL emission spectrum was broad and covered the whole visible range with a maximum at 770–800 nm. Current-voltage characteristics were determined at different temperatures. The optical and electrical characteristics of the developed light emitting diodes are promising for display device applications.

Technological aspects related to the fabrication of buried oxidized porous silicon waveguides (OPSWG) as the influence of swirl defects and a suitable epitaxial method to bury OPSWG have been investigated. The influence of swirl defects on OPSWG performances is presented. The formation of a non-homogeneous porous silicon, caused by swirl defects, results in an incomplete oxidation and in an increase of optical loses. The idea of burying waveguides has been tested by a suitable epi process covering using dichlorosilane and silane as reacting gases. The paper presents and discusses the preliminary results. In this paper, are presented the technological studies related to the fabrication of buried OPSWG: (i) swirl defects influence on the structure and on the guiding properties of OPSWG; (ii) epitaxial deposition process suitable for the realization of defects free silicon layer over the OPSWG.

Emission and excitation spectra of visibly luminescing porous Si structures subjected to a long‐term air impregnation are analyzed. A red shift of emission spectrum with increasing initial porosity is reported. A correlation of excitation spectra with the energy of Γ’25‐Γ15 transition in Si monocrystal is found in the samples differing in the initial porosity. The results seem to be hard to explain in terms of the quantum‐confinement models in their present state. An alternative model based on band‐gap widening in heavily doped silicon structures is considered as well.

The Oxidized Porous Silicon Waveguides (OPSWG) present the chance to realize waveguide in the visible range compatible with integrated circuit (IC) fabrication technology. In OPSWG the light is confined in dense silica surrounded by a buffer of porous oxidized silicon. In this paper some of the results of the European project OLSI N degree(s) 28.934 are discussed. The waveguides were fabricated using p-doped (100) and n-doped (100) and (111) silicon wafers to investigate the influence of the doping type and of silicon crystal orientation on the guiding properties and the thickness of the buffer layer was varied from 1 micrometers to 2.5 micrometers changing the anodization regimes and the propagation losses were measured. Two different topology of mask have been used to determine propagation and planar bending losses. Buried OPSWG, realized depositing one micron poly- silicon layer on top of waveguides, have been thermally treated and measurements have not shown a great difference in terms of propagation losses with surface OPSWG.

This work reports on the CMOS-SOI devices based on porous silicon technology (PST) opening the possibility of wafer scale integration realizing on-chip optoelectronic integrated circuits by the PST. Silicon on insulator (SOI) structure based on the preferential anodization of n+ layer within n-/n+/n- were realized. Standard n-type Si (100) have been used as initial substrates. N+ layer have been formed by Sb ion implantation into the front and backside of the substrates followed by annealing. Then an epitaxial layer has been grown on the front of the wafers and projection photolithography using reactive ion etching of both the mask and the epitaxial layer has been used to define three dimensional pattern of islands wherein device components are formed. Characteristics and device layout are presented for partially depleted devices used to build ring oscillator showing that a 1.2 micron resolution in SOI porous silicon technology is comparable with a 0.5 micron CMOS technology.

It is common knowledge that silicon emits visible light in its breakdown condition, but it is also known to have low efficiency. In this letter, we report an in-depth analysis of data for light emitting devices based on porous silicon. A theoretical model of luminescence from reverse biased p-n junction has been developed for this n-type porous silicon–aluminium Schottky junction to explain the higher efficiency of these electroluminescence devices in comparison with that from a reverse biased p-n junction structure. Through this model, it is possible to understand the steps that are necessary to improve the efficiency of porous-aluminum Schottky junction.

The work presented, that is a part of the ongoing European project OLSI no. 28934, overcomes problems by an OPSWG (oxidized porous silicon waveguide). In order to provide confinement and propagation of light within the waveguide (WG), the guiding region (core) has to have a higher refractive index than the surrounding cladding regions. Such construction of a WG can be provided by a variation of anodization regimes during the PS (porous silicon) formation. The technological process of the OPSWG fabrication consists of three main steps: (a) anodization of Si through the openings in a mask to form PS; (b) thermal oxidation of PS; (c) high temperature densification of OPS.

Infrared photoluminescence (PL) and electroluminescence (EL) from erbium-doped porous silicon (PSi) structures are studied. The PL and EL from the Er-doped PSi structures and the absence of silicon band edge recombination, point defect, and dislocation luminescence bands suggest that the Er-complex centers are the most efficient recombination sites. PSi multilayers with very high reflectivity (R ≥ 90%) in the 1.5 gim range have been incorporated in the structures resulting in a PL enhancement of over 100%. Stable and intense EL is obtained from the Er-doped structures. The EL spectrum is similar to that of the PL, but shifted towards higher energy. The unexpected shift in emission opens up the possibility for erbium related luminescence to encompass a larger part of the optimal wavelength window for fiber optic communications.

Integrated optical waveguides based on oxidized porous silicon were fabricated by means of traditional silicon technology. Near- field pattern and out-of-plane scattering losses were measured to characterize optical properties of the waveguides. Strong confinement of light within the core of the waveguides as well as optical losses of about 5 dB/cm have been demonstrated in the visible range. The achieved results make the waveguides promising in optoelectronics use.

We have developed an original technology to fabricate channel waveguides on monocrystalline silicon wafers, consisting of selective anodization followed by thermal processing. The obtained oxidised porous silicon waveguides show waveguiding properties, moreover, due to the fabrication process, the waveguides are placed just under the surface of the silicon wafer. A hydrogenated amorphous silicon film has been grown on top of the waveguide by a low temperature process, then aluminum contacts have been formed by standard lithography. Different device structures (photodiodes and photoresistors) are presented. Current/voltage properties in the dark and under light excitation accompanied with capacitance/voltage measurements have been used to develop a band diagram model.

The first successful attempt to integrate on-chip optical waveguides based on oxidized porous silicon and amorphous silicon photodetectors have been demonstrated. Buried channel waveguides were performed by thermal oxidation of porous silicon. Amorphous silicon photodetectors were fabricated on the waveguides. Different device structures as well as their performance attributes are exhibited. The devices were demonstrated to have photocurrent characteristics promising for optoelectronic applications.

CMOS devices fabricated on Silicon-On-Insulator (SOI) substrates offer several advantages over bulk silicon due to their low power consumption, and inherent immunity to single event and transient upsets as a result of their small active volumes [1]. There are several different technologies to create SOI structures. Thermal oxidation of porous silicon (PS) is a promising technique for the fabrication of high-quality SOI: in contrast to other SOI methods, the Si islands formed are undamaged monocrystalline silicon [2–7].

The propagation losses are evaluated for the first time in curved integrated (buried) optical waveguides (WGs) based on oxidized porous silicon. In the visible red range, the losses decrease from 20 to 5 dB per 90° bending (for about 0.4 dB/cm loss in the straight WG) when the WG curvature radius increases from 125 to 2500 μm. The main component of the total bending losses in WGs is related to the coupling loss on the passage from straight to curved WG parts. Additional losses are introduced by the regions of incompletely oxidized porous silicon on the walls of curved WGs.

We demonstrate current induced visible light emission from Schottky junctions between aluminium electrodes and porous silicon formed by electrochemical etching of degenerate n+ -type silicon. HF concentration and anodizing current were chosen to yield preparation conditions in the transition region between electropolishing and porous silicon formation regimes. The light emitting diodes were formed by magnetron sputtering of aluminum on the porous silicon surface. Visible electroluminescence (EL) was recorded when dc or ac voltages larger than 4 V were applied between the aluminium electrodes. The visible EL appears in the dark, at the edge of the electrodes at a reverse bias of 5-6 V. The intensity of emitted light increases with applied voltage; at applied bias higher than 7 V the light emitted was observable by the naked eye at normal daylight. Compared to forward bias solid state contact porous silicon devices, the structure has an increased stability (after 100 hours of continuous operation under a 7 V reverse bias, no appreciable modification was observed in emission intensity). The main features of this electroluminescence are very similar to the ones observed under avalanche breakdown of silicon p-n junctions.

Slightly modified CMOS process has been used for the formation of lateral pn junctions in SOI structures based on oxidized porous silicon. Under forward bias these junctions emit infrared light at 1120 nm. Under reverse bias in the breakdown regime the pn junctions demonstrate both infrared and visible light emissions with efficiencies of 10 −4 and 10 −7 , respectively. The beneficial influence of SOI structures on electroluminescence characterictics of light-emitting pn junctions has been established.