Porous Silicon Wafers Research Articles

Performance of high sensitive heterojunction CuS/porous silicon photodetector

In this work, copper sulfide (CuS) nanostructure was deposited on a porous silicon wafer for the visible light by spray pyrolysis method. Through this, a series of devices were suggested as a part of the deposit concentration of CuS on n-type porous silicon. Simultaneously, the physical features of the attained film were illustrated. FESEM exhibited that the average nanoparticle diameter increased with the concentration of CuS at orientation (100) and was found to be 47.84 nm, 56.36nm and 71.32nm, while the average diameter at (111) orientation was found to be 37.64 nm, 41.46nm, 55.22 nm of 0.1, 0.3 and 0.5M respectively. In addition to the atomic force microscope (AFM) showed the roughness and uniformity of the CuS/PSi fabricated decreased with increasing concentration of CuS, In detail, the attained photo-responsivity and specific detectivity were observed to be 210 mW/A, 340 mW/A and 3×1010 Jones, 4.2×1010 Jones at orientation (100 )using concentration of 0.1M and 0.5M respectively . On the other hand, the photo-responsivity and specific detectivity were observed to be 260 mW/A, 380 mW/A and 1.8 ×1010 Jones, 4.5×1010 Jones at orientation (111) using concentrations of 0.1M and 0.5M respectively. The presented work shows a substitutional system for an economical and environmentally friendly optoelectronic scheme. The photo-responsive considered to be in a positive linear relationship with the used concentration.

Vegetal melanin-induced radiative recombination centers in porous silicon

Melanin has attracted significant attention in recent years due to its optoelectronic properties exploited in micro and nano-bioelectronic applications. Herein, were report on the photoluminescence tuning of porous silicon (PSi) functionalized with melanin. PSi was prepared through an electrochemical etching process applying a density current of 2.8 mA/cm2 to a silicon wafer using an electrolyte composed of HF and ethanol (1:1). The melanin/PSi heterojunction interface was created by drop casting a melanin solution (0.1 mg/mL in dimethyl sulfoxide) using different volumes of 10, 30 and 50 μl onto a PSi wafer. A remarkable increment of the photoluminescence intensity in the melanin/PSi interface as compared to the pristine PSi was observed through steady-state experiments. Moreover, a pronounced blue-shift (50 nm) of pristine PSi emission maximum as compared to melanin/PSi interfaces was also recorded. This behavior could be ascribed to the generation of radiative recombination centers as indicated by an increment of silicon-hydrogen (Si–H) and silicon-oxygen (Si–O) defects formed in the PSi upon interaction with the melanin, as proven by infrared (FT-IR) experiments. Time-resolved experiments revealed a remarkable decrease in the decay times of the melanin/PSi composites moving from microsecond-time components in the pristine PSi towards nanosecond decay times when the highest amount of melanin was employed, indicative of an increment of radiative recombination centers. Surface morphology changes of the composites were monitored by scanning electron microscopy (SEM), displaying the formation of small grains of melanin on the surface of the PSi up to the appearance of a melanin thin film when low and high amounts of melanin were used, respectively. This study demonstrates the enormous potential of melanin-PSi heterojunctions to provide a novel and sustainable solution for developing (bio)optoelectronic devices.

The impact of laser energy on the photoresponsive characteristics of CdO/Si visible light photodetector

In this article, cadmium oxide (CdO) was deposited using pulsed laser deposition approach on porous silicon (Si) wafer for visible light photodetector application, through which a series of devices were proposed as a function of the deposition energy. The microstructural as well as optical characteristics of the prepared film/s were demonstrated, respectively, using x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and ultraviolet visible light spectroscopy (UV–Vis) analysis. In details, the UV–Vis analysis revealed the occurrence of optical band gaps within the range of 2.38–2.42 , while an average nanoparticle diameter was found to be 45 using FE-SEM technique. This in turn demonstrated a sound relation with the photoresponsive behavior of the attained photodetectors. A photoresponsivity and specific detectivity of 1.9 and Jones were attained using 700 laser energy. In the meanwhile, the estimated response/recover time of the addressed laser energy was found to be 300 and 340 , respectively. The photo-responsive characteristics of the fabricated devices were found to be in positive linear correlation with the applied laser energy.

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers.

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Unprecedentedly Low CO2 Transport through Vertically Aligned, Conical Silicon Nanotube Membranes.

Nanotube membranes could show significantly enhanced permeance and selectivity for gas separations. Up until now, studies have primarily focused on applying carbon nanotubes to membranes to achieve ultrafast mass transport. Here, we report the first preparation of silicon nanotube (SiNT) membranes via a template-assisted method and investigate the gas transport behavior through these SiNT membranes using single- and mixed-gas permeation experiments. The SiNT membranes consist of conical cylinder-shaped nanotubes vertically aligned on a porous silicon wafer substrate. The diameter of the SiNT pore mouths are 10 and 30 nm, and the average inner diameter of the tube body is 80 nm. Interestingly, among the gases tested, we found an unprecedentedly low CO2 permeance through the SiNT membranes in single-gas permeation experiments, exceeding the theoretical Knudsen selectivity toward small gases/CO2 separation. This behavior was caused by the reduction of CO2 permeability through the blocking effect of CO2 adsorbed in the narrow pore channels of the SiNT cone regions, indicating that CO2 molecules have a high affinity to the native silicon oxide layer (∼2 nm) that is formed on the inner walls of SiNTs. SiNT membranes also exhibited enhanced gas permeance and water flux as compared to classic theoretical models and, as such, may prove useful as a new type of nanotube material for use in membrane applications.

Structural and Optical Properties for Nanostructure (Ag2O/Si & Psi) Films for Photodetector Applications

Ag2O (Silver Oxide) is an important p-type (in chasm to most oxides which were n-type), with a high conductivity semiconductor. From the optical absorbance data, the energy gap value of the Ag2O thin films was 1.93 eV, where this value substantially depends on the production method, vacuum evaporation of silver, and optical properties of Ag2O thin films are also affected by the precipitation conditions. The n-type and p-type silicon substrates were used with porous silicon wafers to precipitate ±125 nm, as thick Ag2O thin film by thermal evaporation techniques in vacuum and via rapid thermal oxidation of 400oC and oxidation time 95 s, then characterized by measurement of XRD, optical properties and scanning electron microscopy properties (SEM). Maximum value of photo response obtained from p-Ag2O/p-PS/Si photodetector results revealed two peak sat 600 nm and 800 nm. According to the x-ray diffraction four peaks appear, (111), (200), (110) and (311) Ag, respectively, (polycrystalline film) and lattice constant of (4.077 Å). Also the results showed a sharp increasing in the absorption-wave length plot of Ag2O film at UV and IR regions. The accumulation of the stars-like are semi-regular of the Ag2O nanocrystals on the surface of p-type PS and the other diffuse inside the pores in a nearly uniform distribution with a different grain size on the surface. The results of the dislocation density and strain are decreased with the grain size increasing.

Detachment yield statistics for kerfless wafering using the porous silicon process

The porous silicon (PSI) process is a wafering method to fabricate high quality kerfless crystalline Si wafers by epitaxial wafer growth on porous Si and subsequent detachment from a reusable substrate wafer. The process yield is a key parameter for the economic viability of the PSI process. We experimentally demonstrate the detachment of 59 out of 62 PSI wafers with a size of 10 × 10 cm2, and separation layer etch current densities of 105–120 mA/cm2 for electrochemically etching the porous Si, and for substrate wafers with a resistivity of 15.7–16.9 mΩcm. We discuss the statistics of how to deduce a detachment probability from this. From our experiments, we determine a detachment yield of at least 88% with an error probability of 5%. The demonstration of a 99% detachment yield with an error probability of 5% would require at least 300 successfully detached wafers with no failed detachment. Samples have a minority carrier density ranging from 1 to 1.7 ms before any external gettering, which demonstrates the high electric quality of the PSI wafers.

Effect of photo chemical etching and electro chemical etching on the topography of porous silicon wafers surfaces

In This research we study the effect of photo chemical etching and electrochemical etching on topography of porous silicon surfaces, the results showed that photo chemical etching produced roughness silicon layer which can have thickness be less of porous silicon layer which is produced by electro chemical etching When all the wafers have same etching time and hydrofluoric solution (HF) concentration, the wafers have same resistance (10 Ω.cm).
 Also the results showed the roughness of porous silicon layers produced by electro chemical method which is bigger than the roughness of porous silicon layers produced by photo chemical method and the results of roughness of porous silicon layers, Pore diameter and porous layer thickness were produced by electro chemical method (1.55(µm) ((0.99(µm)) and ((1.21(µm) respectively), the results of roughness of porous silicon layers, Pore diameter and porous layer thickness were produced by photo chemical method 0.63)) nm -1.55)) (µm) ),so the (84.9 (nm)- and (3.94(nm) respectively .
 This is reinforces because of using the electro chemical to etching the wafer surf ace of bulk silicon and changing it to roughness silicon surface be share in success of many practicalities.

Porous Silicon as a Platform for Radiation Theranostics Together with a Novel RIB-Based Radiolanthanoid.

Mesoporous silicon (PSi) is biocompatible and tailorable material with high potential in drug delivery applications. Here, we report of an evaluation of PSi as a carrier platform for theranostics by delivering a radioactive ion beam- (RIB-) based radioactive lanthanoid into tumors in a mouse model of prostate carcinoma. Thermally hydrocarbonized porous silicon (THCPSi) wafers were implanted with 159Dy at the facility for radioactive ion beams ISOLDE located at CERN, and the resulting [159Dy]THCPSi was postprocessed into particles. The particles were intratumorally injected into mice bearing prostate cancer xenografts. The stability of the particles was studied in vivo, followed by ex vivo biodistribution and autoradiographic studies. We showed that the process of producing radionuclide-implanted PSi particles is feasible and that the [159Dy]THCPSi particles stay stable and local inside the tumor over seven days. Upon release of 159Dy from the particles, the main site of accumulation is in the skeleton, which is in agreement with previous studies on the biodistribution of dysprosium. We conclude that THCPSi particles are a suitable platform together with RIB-based radiolanthanoids for theranostic purposes as they are retained after administration inside the tumor and the radiolanthanoid remains embedded in the THCPSi.

High-Power and Safe Lithium Metal Battery in 3D Substrate

The use of 3D structures has been shown to have the high potential for solving several problems that are currently preventing the performance improvements in lithium batteries. The high-surface area structures can provide elimination of dendrites and elimination of safety concerns, improved energy density and specific energy, high power density, low cost per kWh and improvement in cycle life. Compared with traditionally designed battery electrodes three-dimensional structures also enable short diffusion path in the active mass, better current collection and lower impedance. A perfectly engineered three-dimensional structure is demonstrated using porous silicon. Both anode and cathode can be fabricated on the porous substrate, leading to numerous improvements in performance. A lithium metal anode in porous silicon is shown to be dendrite-free for over 200 cycles as a result geometrical effects in suppressing dendrite growth and low current density. The suppression of dendrites enables the use of lithium metal anodes and eliminating the safety concerns. Both anode and cathode also show improved specific capacity as a result of lower overall impedance and better utilization of the active material; as well as higher power density due to larger three-phase boundary and perfectly arranged active material inside uniformly spaced pores. A complete cell based on the porous silicon structure can use any anode and cathode material; and can therefore be optimized for a particular application or requirements. It is also amenable to use of both liquid and solid electrolytes. A design is demonstrated that enables lithium metal air battery using a solid electrolyte. Another design shows a monolithic full cell within a single porous silicon wafer, eliminating the need for a separator or additional packaging. Results of a half-cell, full cell and symmetrical cell testing are presented. The half-cell testing demonstrates the basic behavior of the porous structure and shows current densities in the excess of 5 mA/cm2 (geometrical or projected surface area), but with a low current density per true surface area. The symmetrical cell testing shows stable anode cycling and absence of dendrites for over 200 cycles, while the full cell testing proves the feasibility of pairing the porous silicon metal lithium anode with several conventional cathode materials.

PASSIVATION OF CRYSTALLINE SILICON ON POROUS SILICON SURFACE TREATED BY ERBIUM OXIDES (Er2O3) FOR ENHANCEMENT THE PHOTOVOLTAIC PROPERTIES

The aim of this paper is to study the effect of erbium oxide (Er2O3) on porous silicon (PS) wafers used for photovoltaic application. An immersion of PS wafers in Er2O3 solution can be used to enhance light trapping and form an efficient surface by passivation process. PS was prepared by the stain-etching method and doped by Er species. In fact, the topography was investigated by the scanning electron microscope (SEM). In addition, the spectral behaviors of the reflectivity and the photoluminescence were discussed. The dependence of minority carrier lifetime was evaluated by means of the Quasi-Steady-State Photoconductance technique (QSSPC). Besides, an enhancement in lifetime was observed. A framework is provided for estimating an efficiency improvement in studied films which will help to guide the development of improved energy-efficient.

Kerfless epitaxial silicon wafers with 7 ms carrier lifetimes and a wide lift-off process window

Silicon wafers contribute significantly to the photovoltaic module cost. Kerfless silicon wafers that grow epitaxially on porous silicon (PSI) and are subsequently detached from the growth substrate are a promising lower cost drop-in replacement for standard Czochralski (Cz) wafers. However, a wide technological processing window appears to be a challenge for this process. This holds in particularly for the etching current density of the separation layer that leads to lift-off failures if it is too large or too low. Here we present kerfless PSI wafers of high electronic quality that we fabricate on weakly reorganized porous Si with etch current densities varying in a wide process window from 110 to 150 mA/cm2. We are able to detach all 17 out of 17 epitaxial wafers. All wafers exhibit charge carrier lifetimes in the range of 1.9 to 4.3 ms at an injection level of 1015 cm−3 without additional high-temperature treatment. We find even higher lifetimes in the range of 4.6 to 7.0 ms after applying phosphorous gettering. These results indicate that a weak reorganization of the porous layer can be beneficial for a large lift-off process window while still allowing for high carrier lifetimes.

4.5 ms Effective Carrier Lifetime in Kerfless Epitaxial Silicon Wafers From the Porous Silicon Process

Kerfless silicon wafers epitaxially grown on porous silicon (PSI) and subsequently detached from the growth substrate are a promising candidate for reducing the cost of the silicon wafer, which is particularly important for silicon photovoltaics. However, the carrier lifetime of these epitaxial wafers has to be at least as high as that of today's standard Czochralski (Cz)-grown wafers in order to become competitive. Here, we compare the measured lifetimes of n -type epitaxial silicon wafers that grow on PSI and epitaxial silicon wafers that grow on nonporous surfaces of epi-ready wafers. The latter are subsequently ground to have free-standing epitaxial wafers. Gettering improves the carrier lifetime of the ground wafers up to 4.2 ms. In contrast, PSI wafers show regions with effective lifetimes of 4.5 ms, even without gettering. This lifetime value is a factor of four larger than lifetimes of Cz wafers which are typically employed in today's PERC solar cells. We model the lifetime measurements with three Shockley–Read–Hall (SRH) defects: two defects that exist in the PSI and in the epi-ready wafer and a third defect that is only present in the epi-ready wafer.

Preparation of SERS Substrates for the Detection of Organic Molecules at Low Concentration

In this paper, we present the results of the preparation of Surface Enhanced Raman Spectroscopy (SERS) substrates by depositing silver nanoparticles (Ag NPs) onto a porous silicon wafer that is produced by the chemical etching process. The influences of the preparation parameters such as resistivity of the silicon wafer, the anodizing current density, etching time to the size of pores were systematically investigated. The SERS substrates prepared were characterised by using appropriate techniques: the morphology and pores size by scanning electron microscope (SEM), the SERS activity by Raman scattering measure of organic molecules malachite green (MG) embedded into the substrate at room temperature. Our experimental results show that a home-made Raman microscope system could be efficiently used to detect the MG molecules at the concentration lower than 10-7 M with the prepared SERS substrates which have Ag NPs in the obtained pores of 10 – 40 nm.

Pore-level hydrate formation mechanisms using realistic rock structures in high-pressure silicon micromodels

We report pore-level visualization of CO2 and CH4 gas hydrate formation with dynamic growth patterns within a 2D porous silicon wafer micromodel with realistic pore shapes and sizes. Direct observation of pore-scale hydrate growth patterns at reservoir conditions provides an improved framework for fundamental studies of sediment-hosted gas hydrates. The growth pattern and formation rate are discussed with respect to wetting films, fluid distribution, and PT conditions for CH4 and CO2 hydrate. Hydrates appeared initially on the interface between gas spheres and thin water films coating the grain surface, followed by a continuous hydrate growth throughout the pore space. Redistribution of hydrate was observed over several hours at stable conditions. Furthermore, repeated hydrate formation occurred more rapidly and at higher temperatures than during primary formation. The understanding of pore-scale growth of sedimentary gas hydrate has great value in describing hydrates in a geological setting and toward production of a vast energy resource. It may also be a key feature in CO2 storage schemes.

Fabrication of a poly(dimethylsiloxane) microstructured surface imprinted from patterned silicon wafer with a self-cleaning property

Microrod patterns were fabricated on PDMS sheets utilizing porous silicon wafers as templates. The prepared microrod PDMS surface showed high water and oil contact angles. To discuss the mechanism, theoretical contact angles were calculated utilizing Wenzel model and Cassie-Baxter model, and compared with the measured values. Furthermore, it was confirmed that the microrod PDMS surface has self-cleaning property.

Photodegradation activity and stability of porous silicon wafers with (1 0 0) and (1 1 1) oriented crystal planes

Hydrogen-terminated porous Si wafers with (100) and (111) oriented crystal planes were fabricated through a photo-electrochemical etching. It is found that the porosity of silicon wafers and their etch rates are determined as a function of crystal orientation. Due to the anisotropic etching behavior of single-crystal silicon, the hydrogen-terminated porous Si (100) wafers exhibit not only more excellent photodegradation activity but also stronger stability for methyl orange degradation than hydrogen-terminated porous Si (111) wafers under visible light irradiation. For the unetched Si wafers, however, the photodegradation activities of methyl orange exhibit a contrary conclusion.

Ultrasonic characterization of electrochemically etched porous silicon

This paper presents a non-destructive characterization of porous silicon wafer using ultrasound based on the strong relationship between porosity and acoustical parameters. Transmission coefficients are measured using broadband water immersion method and compared to theoretical ones using a genetic algorithm optimization. Retrieved parameters are thickness and acoustic impedance. Porosity is deduced from acoustic impedance. Two set of porous silicon wafers, with different porosities and thicknesses, have been etched using hydrofluoric acid based solution and galvanostatic etching method. Their thicknesses and porosities are measured using destructive methods after ultrasonic measurements. A good agreement is observed. Hypothesis to explain discrepancies are proposed.

Hydrogen storage in hierarchical nanoporous silicon-carbon nanotube architectures

SUMMARY A porous silicon (pSi) wafer with a hierarchical, nanoporous architecture and pure single wall carbon nanotubes (SWNTs) have been combined by electrophoretic infiltration to form a unique hybrid pSi-SWNT hydrogen storage system. The pSi architecture was fabricated by anodic etching of silicon wafers in alcoholic solutions of hydrogen fluoride. Direct hydrogen dosing to adsorb hydrogen on the pSi-SWNT hybrid, pure pSi, electrochemically charged pSi and SWNTs, and pure SWNTs, followed by temperature programmed desorption measurements, were used to quantify the hydrogen adsorption process. The results indicate an increased hydrogen storage capacity at a lower temperature in the pSi-SWNT system relative to that from pure pSi, and pure and charged SWNTs. In addition, hydrogen adsorption in pSi-SWNT is about a factor of 2 to 6 higher than that in pure and charged pSi, and pure and charged SWNTs. Copyright © 2012 John Wiley & Sons, Ltd.