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We are proposing a new subfield of engineering, called Inclusion Engineering, that is defined as the use of engineering tools, design, research, and thinking to create environments through which individuals whose abilities and contributions would previously have been marginalized by society can become productive members within society, and at the same time, organizations and society as a whole are made better through more full engagement of the broad spectrum of human abilities.

Systematic studies of the relaxation processes in nm-thick Er-doped SiO2/nc-Si multilayers have been conducted using cw photoluminescence and time-resolved photoluminescence. The size of the Si nanocrystals is determined by thickness of the Si layer. The distance between the Si nanocrystals and the Er ions in the SiO2 layers is fixed between 0 and 2.2 nm. An efficient energy transfer from amorphous and crystalline Si nanostructures to Er is observed and leads to a strong Er photoluminescence at 1535 nm, which increases as the Si layer thickness decreases. The fast Er photoluminescence (μs lifetime) results from energy transfer from a-Si nanostructures and the slow Er emission (ms lifetime) is caused by energy transfer from confined states in nc-Si. The transfer time was estimated to be 20 ± 5 ns by a direct time-resolved photoluminescence experiment. A model is proposed to explain these results.

Nanopore formation in silicon films has previously been demonstrated using rapid thermal crystallization of ultrathin (15 nm) amorphous Si films sandwiched between nm-thick SiO2 layers. In this work, the silicon dioxide barrier layers are replaced with silicon nitride, resulting in nanoporous silicon films with unprecedented pore density and novel morphology. Four different thin film stack systems including silicon nitride/silicon/silicon nitride (NSN), silicon dioxide/silicon/silicon nitride (OSN), silicon nitride/silicon/silicon dioxide (NSO), and silicon dioxide/silicon/silicon dioxide (OSO) are tested under different annealing temperatures. Generally the pore size, pore density, and porosity positively correlate with the annealing temperature for all four systems. The NSN system yields substantially higher porosity and pore density than the OSO system, with the OSN and NSO stack characteristics fallings between these extremes. The higher porosity of the Si membrane in the NSN stack is primarily due to the pore formation enhancement in the Si film. It is hypothesized that this could result from the interfacial energy difference between the silicon/silicon nitride and silicon/silicon dioxide, which influences the Si crystallization process.

We have developed electroosmotic pumps (EOPs) fabricated from 15-nm-thick porous nanocrystalline silicon (pnc-Si) membranes. Ultrathin pnc-Si membranes enable high electroosmotic flow per unit voltage. We demonstrate that electroosmosis theory compares well with the observed pnc-Si flow rates. We attribute the high flow rates to high electrical fields present across the 15-nm span of the membrane. Surface modifications, such as plasma oxidation or silanization, can influence the electroosmotic flow rates through pnc-Si membranes by alteration of the zeta potential of the material. A prototype EOP that uses pnc-Si membranes and Ag/AgCl electrodes was shown to pump microliter per minute-range flow through a 0.5-mm-diameter capillary tubing with as low as 250 mV of applied voltage. This silicon-based platform enables straightforward integration of low-voltage, on-chip EOPs into portable microfluidic devices with low back pressures.

Frontiers in Biological Detection: From Nanosensors to Systems VII, edited by Benjamin L. Miller, Philippe M. Fauchet, Brian T. Cunningham, Proc. of SPIE Vol. 9310, 931001 · © 2015 SPIE CCC code: 1605-7422/15/$18 · doi: 10.1117/12.2183941Proc. of SPIE Vol. 9310 931001-1Downloaded From: http://proceedings.spiedigitallibrary.org/ on 12/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.aspx

Infrared photoluminescence (PL) and electroluminescence (EL) near 1.5 μm from Er-doped SiO2/nc-Si multilayers are reported. A novel, effective method of lateral carrier injection is demonstrated in forward bias. The in-plane geometry increases the current density over those typically reported from Er doped SiO2 layers containing Si nanocrystals under vertical carrier injection. The observed strong PL under off-resonance excitation for Er in SiO2 and EL under forward bias are very promising for Si-based light sources – the missing link in an all-silicon on-chip optical interconnection system.

Label-free sensing strategies are an intensely studied and increasingly used alternative to signal amplification via fluorescent labels and enzymatic methods. This article discusses one class of optical sensors, termed "photonic crystals", that effectively amplify binding events (such as analyte capture) via strong light-matter interactions.

Ultrathin porous nanocrystalline silicon (pnc-Si) membranes metallized with gold are used as flexible conductive electrodes in chemical capacitive vapor sensor. This use of a porous electrode simplifies the conventional parallel-plate design of typical sensors. pnc-Si is a 15 nm thick membrane material with pore sizes ranging from 5 to 50 nm and porosities from

A photonic crystal (PhC) waveguide based optical biosensor capable of label-free and error-corrected sensing was investigated in this study. The detection principle of the biosensor involved shifts in the resonant mode wavelength of nanocavities coupled to the silicon PhC waveguide due to changes in ambient refractive index. The optical characteristics of the nanocavity structure were predicted by FDTD theoretical methods. The device was fabricated using standard nanolithography and reactive-ion-etching techniques. Experimental results showed that the structure had a refractive index sensitivity of 10−2 RIU. The biosensing capability of the nanocavity sensor was tested by detecting human IgG molecules. The device sensitivity was found to be 2.3 ± 0.24 × 105 nm/M with an achievable lowest detection limit of 1.5 fg for human IgG molecules. Additionally, experimental results demonstrated that the PhC devices were specific in IgG detection and provided concentration-dependent responses consistent with Langmuir behavior. The PhC devices manifest outstanding potential as microscale label-free error-correcting sensors, and may have future utility as ultrasensitive multiplex devices.

In this work we study the role of fluorine for the selective suppression of porous silicon in localized SOI applications. The formation of porous silicon can be done selectively by controlling the Fermi level in areas to be etched or not etched, which is typically done by adjusting the level of doping. Implanted fluorine in silicon has demonstrated a donor effect upon annealing at low temperature (600 °C), which is reversible as the fluorine outdiffuses during higher temperature annealing (1100 °C). The investigated technique has been used to form crystalline silicon active regions with thickness less than 200 nm completely surrounded by oxidized porous silicon. The electronic integrity of the active area has also been established through nMOS transistor fabrication and characterization (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the application of scanning electrochemical microscopy (SECM) to the measurement of the ion-selective permeability of porous nanocrystalline silicon membrane as a new type of nanoporous material with potential applications in analytical, biomedical, and biotechnology device development. The reliable measurement of high permeability in the molecularly thin nanoporous membrane to various ions is important for greater understanding of its structure-permeability relationship and also for its successful applications. In this work, this challenging measurement is enabled by introducing two novel features into amperometric SECM tips based on the micropipet-supported interface between two immiscible electrolyte solutions (ITIES) to reveal the important ion-transport properties of the ultrathin nanopore membrane. The tip of a conventional heat-pulled micropipet is milled using the focused ion beam (FIB) technique to be smoother, better aligned, and subsequently, approach closer to the membrane surface, which allows for more precise and accurate permeability measurement. The high membrane permeability to small monovalent ions is determined using FIB-milled micropipet tips to establish a theoretical formula for the membrane permeability that is controlled by free ion diffusion across water-filled nanopores. Moreover, the ITIES tips are rendered selective for larger polyions with biomedical importance, i.e., polyanionic pentasaccharide Arixtra and polycationic peptide protamine, to yield the membrane permeability that is lower than the corresponding diffusion-limited permeability. The hindered transport of the respective polyions is unequivocally ascribed to electrostatic and steric repulsions from the wall of the nanopores, i.e., the charge and size effects.

Porous nanocrystalline silicon (pnc-Si) is new type of silicon nanomaterial with potential uses in lab-on-a-chip devices, cell culture, and tissue engineering. The pnc-Si material is a 15 nm thick, freestanding, nanoporous membrane made with scalable silicon manufacturing. Because pnc-Si membranes are approximately 1000 times thinner than any polymeric membrane, their permeability to small solutes is orders-of-magnitude greater than conventional membranes. As cell culture substrates, pnc-Si membranes can overcome the shortcomings of membranes used in commercial transwell devices and enable new devices for the control of cellular microenvironments. The current study investigates the feasibility of pnc-Si as a cell culture substrate by measuring cell adhesion, morphology, growth and viability on pnc-Si compared to conventional culture substrates. Results for immortalized fibroblasts and primary vascular endothelial cells are highly similar on pnc-Si, polystyrene and glass. Significantly, pnc-Si dissolves in cell culture media over several days without cytotoxic effects and stability is tunable by modifying the density of a superficial oxide. The results establish pnc-Si as a viable substrate for cell culture and a degradable biomaterial. Pnc-Si membranes should find use in the study of molecular transport through cell monolayers, in studies of cell-cell communication, and as biodegradable scaffolds for three-dimensional tissue constructs.

A novel method of selecting a subset of Bloch modes in silicon-based photonic crystal microring resonators (PhCR)s is demonstrated. Bloch modes in the PhCR are calculated, and their intensity beating patterns are analyzed. Based on the different spatial intensity distribution for each resonance, a subset of resonances is out-coupled using an output coupler waveguide (CWG) which is positioned at an angle θ=90° with respect to the input CWG. As shown in theory and experiment, resonances with an even mode number are selected, while resonances with an odd mode number are rejected. The highest contrast between mode selection and mode rejection is ∼9 dB in the experiments. This approach opens another design freedom for ring resonator-based devices and could potentially reduce the footprint of microring resonator-based multiplexers and add-drop filters.

We report on the fabrication of a macroporous silicon diode that successfully operates in a photovoltaic mode of energy conversion. Typical device structures are fabricated on 4″, Cz grown, , p-type, 5 – 30 Ω-cm, Si substrates and make use of random or pre-patterned macroporous silicon films up to 100 μm thick with pores ∼1 μm in diameter and a center-to-center pore spacing of 2.5 μm. Phosphorous dopants are introduced throughout the porous silicon region with a newly adapted technique based on proximity rapid thermal diffusion. This development effort has enhanced the uniformity of dopant diffusion into the pores and subsequently improved device performance. The resulting p-n diode within the porous silicon is of a three-dimensional nature and exhibits an extremely high internal surface area up to ∼6690 cm2/cm3. To our knowledge, this is the first use of such a technique to fabricate conformal, three-dimensional p-n junctions for photovoltaic applications. The large internal surface area of this diode makes it applicable to next generation photovoltaics. Moreover, the porous silicon within this device is not simply an antireflection coating; rather it is a light trapping medium that has the ability to become a large surface area diode and can serve as a host matrix for photoactive compounds. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Interconnect has become a primary bottleneck in integrated circuit design. As CMOS technology is scaled, it will become increasingly difficult for conventional copper interconnect to satisfy the design requirements of delay, power, bandwidth, and noise. On-chip optical interconnect has been considered as a potential substitute for electrical interconnect in the past two decades. In this paper, predictions of the performance of CMOS compatible optical devices are made based on current state-of-art optical technologies. Electrical and optical interconnects are compared for various design criteria based on these predictions. The critical dimensions beyond which optical interconnect becomes advantageous over electrical interconnect are shown to be approximately one tenth of the chip edge length at the 22 nm technology node.

A three-dimensional p-n diode structure is presented for the generation of energy via photovoltaic and betavoltaic modes of operation. Macroporous Silicon (MPS) has a large degree of internal surface area and its vertically oriented pores, which extend deep into the bulk of the Si substrate, allow for the creation of three-dimensional structures. In this device the MPS will not only serve as a means for creating 3D diode structures, it will also serve as a host matrix for a tritium isotope which emits energetic beta particles. By varying electrochemical etching conditions and using a prepatterning technique, 1.1 μm diameter pores with a spacing of 2.5 μm were achieved. The p-n junction was created using a rapid thermal process (RTP) which relies on the diffusion from an n-type solid source into the MPS. To ensure the quality of the diode structure, devices were tested using a light source which resulted in a photovoltaic response. Finally, betavoltaic operation was demonstrated by exposing devices to a tritium gas source. The average energy conversion efficiency of the first generation 3D diode was one order of magnitude higher than that of a similar planar device.

Photochemical etching of silicon assisted by two-photon absorption (TPA) in the presence of hydrofluoric acid (HF) is demonstrated using a below-bandgap femtosecond laser source. We investigate the morphology of the etched silicon as a function of the laser power, exposure time, as well as the substrate doping level. Self-organized periodic silicon trenches with ∼150 nm spacing were observed at the etch front as the initial stage of the TPA photochemical etching process. Since the etching front can be precisely controlled by the focal point, this technique can be used for writing silicon microfluidic systems and for 3D micromachining.

A novel cell interface has been constructed on porous silicon. We have demonstrated that nano- to macro-scale porous architectures have promising osteoconductive potentials. Macroporous silicon (pore opening 1-2 μm) is especially favorable for osteoblast adhesion, growth, protein synthesis and mineralization. An electronic/optoelectronic controllable medical implant with both scaffolding and drug delivery functions may be created for orthopaedic tissue engineering with this material.

Integration of electrical and fluidic systems for the design and fabrication of a system-on-chip (SOC) capable of sensing various liquid phase solvents is reported. A monolithic integration strategy makes use of macroporous silicon (MPS) as a gateway to interface the electrical and fluidic domains. In this application, the MPS material, acting as a sensing membrane, is used in a flow-through structure to transport an analyte from fluidic channels on one side of the chip to sensing electrodes on the other. A fluid-oxide-semiconductor interface results in the modulation of a space charge region in the semiconductor where real-time measurements are used to detect and distinguish between the presences of various solvents. The fluidic system has delivered sample volumes as small as 2 mul. Selected test solvents (i.e. acetone, ethanol, isopropyl alcohol, methanol, and toluene) have generated a measured change in capacitance up to 11%. A practical application of this sensor was demonstrated by monitoring various concentrations of isopropyl alcohol in a water supply. Undiluted samples provide characteristic responses that can be used for signature identification. The sensing device has a high degree of reusability and does not require heating or other solvent removal methods often necessitated in other sensing devices

A label-free biosensor was demonstrated using macroporous silicon (pore size100 nm) one-dimensional photonic band gap structures that are very sensitive to refractive index changes. In this study, we employed Tir-IBD (translocated Intimin receptor-Intimin binding domain) and Intimin-ECD (extracellular domain of Intimin) as the probe and target, respectively. These two recombinant proteins comprise the extracellular domains of two key proteins responsible for the pathogenicity of enteropathogenic Escherichia coli (EPEC). The optical response of the sensor was characterized so that the capture of Intimin-ECD could be quantitatively determined. Our result shows that the concentration sensitivity limit of the sensor is currently 4 microM of Intimin-ECD. This corresponds to a detection limit of approximately 130 fmol of Intimin-ECD. We have also investigated the dependence of the sensor performance on the Tir-IBD probe molecule concentration and the effect of immobilization on the Tir-IBD/Intimin-ECD equilibrium dissociation constant. A calibration curve generated from purified Intimin-ECD solutions was used to quantify the concentration of Intimin-ECD in an E. coli BL21 bacterial cell lysate, and results were validated using gel electrophoresis. This work demonstrates for the first time that a macroporous silicon microcavity sensor can be used to selectively and quantitatively detect a specific target protein with micromolar dissociation constant (Kd) in a milieu of bacterial proteins with minimal sample preparation.

Intrachip optical interconnects (OIs) have the potential to outperform electrical wires and to ultimately solve the communication bottleneck in high-performance integrated circuits. Performance targets and critical directions for ICs progress are yet to be fully explored. In this paper, the International Technology Roadmap for Semiconductors (ITRS) is used as a reference to explore the requirements that silicon-based ICs must satisfy to successfully outperform copper electrical interconnects (IEs). Considering the state-of-the-art devices, these requirements are extended to specific IC components

Porous silicon one-dimensional (1-D) photonic crystal microcavities are fabricated as building blocks for optical modulators. The microcavities consist of porous silicon layers with alternating low and high porosity. Since the pore size is much smaller than the incident wavelength of light, each porous silicon layer is treated as an effective medium with a specific effective refractive index that corresponds to the given porosity. Active tuning of the microcavity resonance is accomplished through electrical actuation of liquid crystals infiltrated into the pores. As the refractive index of the liquid crystals change in response to the external stimulus, the effective refractive index of the porous silicon layers changes and the resonance wavelength shifts accordingly. The resonance wavelength shift creates an optical signal intensity modulation at a particular wavelength. Extinction ratios greater than 10 dB are achievable for these devices. The performance characteristics of the porous silicon photonic crystal microcavities can be tailored to specific applications based on the choice of infiltrated optically active material and the quality factor of the device

Electrical tuning of high refractive index-contrast photonic bandgap (PBG) structures is required for a majority of PBG applications, particularly for integrated optics. When the host material is a semiconductor with poor electro-optical properties, tuning can be achieved by infiltrating the structure with an active optical material. In this paper we analyze the switching of electro-optic material in such structures, and suggest design rules to help achieve electrical tuning. In particular, a design concept that eliminates the electric field screening effects is proposed. The developed rules and concepts are demonstrated by the electrical tuning of liquid crystals inside two-dimensional porous silicon PBG structures. This approach can be generalized to different combinations of semiconductor PBG structures and active optical materials

New nanocomposite materials with large optical nonlinearity are important for the development and miniaturizing of active components and integrated circuits for all-optical signal processing and computing. To enable on-chip integration with silicon microelectronics nonlinear signal processing components compatible with silicon nanophotonics need to be developed. In this paper, we study the nonlinear optical response of silicon-based photonic bandgap (PBG) structures filled with PbSe quantum dot (QD) materials and experimentally demonstrate the feasibility of a new class of nonlinear nanophotonic devices for all-optical signal processing based on such microstructures. Active tuning is demonstrated for both out-of-plane components, with one-dimensional porous silicon PBG microcavities and in-plane components, using one-dimensional PBG waveguide-based microresonators.

Macroporous silicon microcavities for detection of large biological molecules have been fabricated from highly doped n-type silicon. Well-defined controllable pore sizes up to 120 nm have been obtained by systematically optimizing the etching parameters. The dependence of the sensor sensitivity on pore size is discussed. Excellent infiltration inside these macroporous silicon microcavities is demonstrated using 60 nm diameter latex spheres and rabbit IgG (150 kDa; 1Da = 1 g mol–1). The sensing performance of the device is tested using a biotin/streptavidin couple, and protein concentration down to 1–2 μM (equivalent to 0.3 ng mm–2) could be detected. Simulations show that the sensitivity of the technique is currently approximately 1–2 % of a protein monolayer.

Photonic bandgap (PBG) materials offer an attractive and compact way of integrating the building blocks for optical interconnects and optoelectronic circuits. In this work we demonstrate 2-D macroporous silicon PBG structures fabricated using interferometric lithography and electrochemical etching of silicon. Optical measurements match well with simulations. We achieve tuning of the PBG using liquid crystals (LCs) infiltrated inside the porous silicon. Surface treatment methods for controlling the initial LC molecule orientation inside the pores are also demonstrated. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal tuning of silicon-based one-dimensional photonic bandgap microcavities is demonstrated. Thermally induced spectral shifts are caused by both the host silicon matrix and the optically active material infiltrated inside the photonic bandgap structures. The active material leads to the dominant thermal tuning contribution but the effect of the silicon matrix cannot be neglected. The interaction of the temperature dependence of the host matrix with that of the active material is explored. The general trends revealed by the characterization should be relevant for two-dimensional silicon-based photonic bandgap structures as well as other photonic bandgap materials systems. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Porous silicon (PSi) is a versatile material that possesses a wide range of morphologies. There are two main types of microstructures that are widely used and well studied: branchy mesoporous silicon with pore sizes from 10 nm to 50 nm and classical macroporous silicon with pore sizes from 500 nm to 20 μm. Much less work has been done on structures with intermediate pore sizes from 100 nm to 300 nm. Applications such as immunoassays biosensing can greatly benefit from the intermediate morphology due to the larger pore openings compared to mesopores, and increased internal surface compared to classical macropores. In this work we demonstrate well-defined macropore of 150 nm diameter in average and precise control of the porous silicon morphology transition from smooth macropores to branchy mesopores on one substrate with one electrolyte. A multilayer structure (microcavity) consisting of both mesopores and macropores is presented.

A novel electrical sensor platform containing a porous silicon (PSi) layer on a crystalline silicon substrate has been developed in which the electrical contacts are made exclusively on the backside of the substrate allowing complete exposure of the surface to the sensing molecules. The PSi layers were 20 μm thick with an average pore diameter of 1 μm. Real-time measurements of capacitance (C) and conductance (G) were performed and the response produced by the addition of different organic solvents was evaluated. The observed response is attributed to the combined effect of a change in dielectric constant inside the porous matrix and a modification in the depletion layer width in the crystalline silicon structure. A space charge region modulation model was used to explain the effect induced by molecules of different dipole moments, dielectric constants, polarizabilities and water solubilities.

As continued progress towards faster, low power consuming microelectronic devices becomes increasing difficult due to the scaling challenges of electrical interconnects, it becomes even more critical to explore alternative technologies. Tunable porous silicon photonic bandgap structures are viable building blocks for optical interconnects, which present a possible long term solution to the interconnect problem. Forming the structures on a silicon platform provides the advantage of easier integration with current semiconductor processing techniques. In this work, tuning of the optical properties is controlled by liquid crystals (LCs) that are infiltrated into the silicon matrix. Active tuning is demonstrated both out-of-plane, with one-dimensional porous silicon photonic bandgap microcavities, and in-plane, using two-dimensional porous silicon photonic bandgap structures.

An extensive experimental study of optical gain in silicon nanocrystals is under way. Different types of samples have been tested (e.g., nanocrystalline silicon superlattices prepared in Rochester, ion implanted silicon dioxide prepared in Canberra) using different measurement techniques (e.g., variable stripe length method in Trento and in Rochester, prism coupling in Canberra) and different pump laser sources (from femtosecond to cw). All the results presented here have been reproduced in at least two different laboratories, making it unlikely that experimental artifacts play a role. So far, we have observed nsec-duration gain in the visible/near infrared range in nanocrystalline silicon superlattices under high photoinjection conditions with short laser pulses. For other conditions (e.g., lower photoinjection, ion implanted samples with a lower concentration of quantum dots), we have not observed gain.

Si quantum dots (QDs) as small as ∼2 nm in diameter have been synthesized by a variety of techniques. Because of quantum confinement and the elimination of bulk or surface defects, these dots can emit light from the near infrared throughout the visible with quantum efficiencies in excess of 10%. The luminescence wavelength range has been extended to longer wavelengths by the addition of light-emitting rare earths such as erbium (Er). Light-emitting devices (LEDs) have been fabricated and their performances are starting to approach those of direct band gap semiconductor or organic LEDs. A search for a Si QD-based laser is even under way. The state-of-the-art in the materials science, physics, and device development of luminescent Si QDs is reviewed and areas of future research are pointed out.

Films consisting of nanometer-scale silicon crystals with narrow size distribution can be fabricated using a variety of techniques and are of technological interest for nonvolatile semiconductor memory applications. One fabrication technique based on the crystallization of thin amorphous silicon films also shows potential for large-scale production of single isolated nanocrystals for future single-electron transistor and memory applications. A review of the most promising nanocrystalline silicon fabrication techniques and a discussion of current research in the area of crystallized thin-film amorphous silicon are presented in this article.

Macroporous silicon (pore diameter 1-2 microm) was used in an electrical sensor for real time, label free detection of DNA hybridization. Electrical contacts were made exclusively on the back side of the substrate, which allowed complete exposure of the porous layer to DNA. Hybridization of a DNA probe with its complementary sequence produced a reduction in the impedance and a shift in the phase angle resulting from a change in dielectric constant inside the porous matrix and a modification of the depletion layer width in the crystalline silicon structure. The effect of the DNA charge on the response was corroborated using peptide nucleic acid (PNA), an uncharged analog of DNA. The sensitivity and selectivity of the device were characterized and the sensing properties of the porous layer alone were investigated using self-supporting macroporous silicon membranes.

The objective of this work is to use porous silicon (PSi) layers as substrate material to transduce hybridization of DNA into a change in conductance. A coplanar configuration of the contact electrodes allows a complete exposure of the porous silicon layer to the sensing species without the need of top contacts or electrolyte solutions. Synthetic oligonucleotides were infiltrated into the porous silicon layers to sense the hybridization event. Hybridization of a single base sequence to its complementary strand was used as a model to demonstrate the response of the layer to the binding of complex sequences. We hypothesize that the observed response involves the activity of surface states present at the silicon-silicon dioxide (Si-SiO 2 ) interface and sensitive to the change in charge at the surface of the layer.

If porous silicon (PSi) is going to be seriously considered for antireflection (AR) applications in the solar cell industry, it must not only offer superior AR properties, but must also prove minimally disruptive to the current manufacturing process. This limits its application to the final (backend) fabrication steps, after p-n junction formation. Since typical commercial junction depths are on the order of 350 nm, the PSi etching process must only consume a portion of this emitter layer if the electrical properties of these devices are to be maintained. In this study, we have focused on the development of a dynamic etching process to form thin (

We demonstrate tunable mirrors that consist of a porous silicon microcavity infiltrated with liquid crystal molecules. We show theoretically that by utilizing the electro-optic properties of liquid crystals and the sensitivity of the microcavity resonance position to small changes in optical thickness, the porous silicon active mirror can be switched on (high reflectance) and off (low reflectance) by simply applying a voltage. We discuss the issues of obtaining uniform infiltration of liquid crystal molecules in the constricted geometry of the porous silicon microcavity and determining the necessary change in the liquid crystal orientation to achieve a high reflectance contrast. We also present preliminary experimental results showing a greater than 40% change in the reflectance of our active mirror with the application of voltage.

We report photocarrier time-of-flight measurements in diode structures made of highly porous crystalline silicon. The corresponding electron and hole drift mobilities are very small ð