N-type Si Wafers Research Articles

CuO-Functionalized Silicon Photoanodes for Photoelectrochemical Water Splitting Devices.

One main difficulty for the technological development of photoelectrochemical (PEC) water splitting (WS) devices is the fabrication of active, stable and cost-effective photoelectrodes that ensure high performance. Here, we report the development of a CuO/Silicon based photoanode, which shows an onset potential for the water oxidation of 0.53 V vs SCE at pH 9, that is, an overpotential of 75 mV, and high stability above 10 h. These values account for a photovoltage of 420 mV due to the absorbed photons by silicon, as proven by comparing with analogous CuO/FTO electrodes that are not photoactive. The photoanodes have been fabricated by sputtering a thin film of Cu(0) on commercially available n-type Si wafers, followed by a photoelectrochemical treatment in basic pH conditions. The resulting CuO/Cu layer acts as (1) protective layer to avoid the corrosion of nSi, (2) p-type hole conducting layer for efficient charge separation and transportation, and (3) electrocatalyst to reduce the overpotential of the water oxidation reaction. The low cost, low toxicity, and good performance of CuO-based coatings can be an attractive solution to functionalize unstable materials for solar energy conversion.

Tunneling spectroscopy of p-type doping in silicon from boron-containing molecular monolayer

Scanning tunneling spectroscopy was used to investigate surface doping in silicon, based on the grafting of a boron-containing molecular layer and the subsequent thermal diffusion of boron into silicon. Curve fitting of the experimental I(V) characteristics with a planar computation of the tunnel current yields a dopant concentration that is consistent with secondary ion mass spectrometry analyses in the subsurface region. Additional two-point probe electrical measurements performed at variable tip separations indicate a bulk-like transport, that corresponds to a significant diffusion of the boron impurities below the surface of low doped n-type Si wafers. Such results show the interest of multiple-probe scanning tunneling microscopy as a non-invasive technique to determine the electrically active content of doped layers during the fabrication of advanced integrated circuits.

Influence of Si Surface Orientation on Screen-printed Ag/Al Contacts

In this study the influence of the crystallographic surface orientation of n-type Si wafers on the contact formation of Ag/Al thick film pastes to p+-type Si layers is investigated. Therefore, n-type Si wafers with two different crystallographic orientations, namely polished (111) and (100) FZ wafers, with BBr3 based emitter and 75 nm SiNx:H are screen-printed with Ag/Al paste. Then contacts are fired in either a slow firing process or a fast one with the same peak temperature. Afterwards, contacts are prepared for scanning electron microscopy (SEM) analysis. The Ag/Al contact spots show different shapes on the differently oriented surfaces. For the slow firing process, no significant difference in number and size of the contacts spots can be found for the two surfaces. For samples fired in the fast firing process, the density and size of the contact spots on (100)-oriented surfaces is strongly reduced, whereas for the (111) surfaces only a slight reduction in density is visible as compared to the slow firing process.

A Comparison Study of n-type PERT and IBC Cell Concepts with Screen Printed Contacts

In this work we conducted a comparison study of our n-type PERT (BiSoN) and IBC (ZEBRA) cell technologies. We investigated the effect of material quality and base resistivity on the performance and efficiency potential of the two device architectures. We observed only a slight efficiency variation (less than 3%relative) for wafer bulk lifetimes ranging from 1.2-6.5ms and base resistivities from 2-9 Ωcm, with no significant difference between the n-PERT andthe IBC concept. We achieved cell efficiencies, as high as 20.4% for BiSoN concept and 21.5% for ZEBRA on 15.6×15.6 cm2 n-type Cz Si wafers. Additionally, we demonstrated that both cell concepts have a high bifacial performance, both at cell and module level.

Enhanced diode performance in cadmium telluride–silicon nanowire heterostructures

We report on the structural and optoelectronic characteristics and photodetection properties of cadmium telluride (CdTe) thin film/silicon (Si) nanowire heterojunction diodes. A simple and cost-effective metal-assisted etching (MAE) method is applied to fabricate vertically oriented Si nanowires on n-type single crystalline Si wafer. Following the nanowire synthesis, CdTe thin films are directly deposited onto the Si nanowire arrays through RF magnetron sputtering. A comparative study of X-ray diffraction (XRD) and Raman spectroscopy shows the improved crystallinity of the CdTe thin films deposited onto the Si nanowires. The fabricated nanowire based heterojunction devices exhibit remarkable diode characteristics, enhanced optoelectronic properties and photosensitivity in comparison to the planar reference device. The electrical measurements revealed that the diodes have a well-defined rectifying behavior with a superior rectification ratio of 105 at ±5V and a relatively small ideality factor of n=1.9 with lower reverse leakage current and series resistance at room temperature in dark condition. Moreover, an open circuit voltage of 120mV is also observed under illumination. Based on spectral photoresponsivity measurements, the nanowire based device exhibits a distinct responsivity (0.35–0.5AW−1) and high detectivity (6×1012−9×1012cmHz1/2W−1) in near-infrared wavelength region. The enhanced device performance and photosensitivity is believed to be due to three-dimensional nature of the interface between the CdTe thin film and the Si nanowires. The device characteristics observed here reveals that fabricated CdTe thin film/Si nanowire heterojunctions are promising for high-performance and low-cost optoelectronic device applications, near-infrared photodetectors in particular.

Improved diode properties in zinc telluride thin film-silicon nanowire heterojunctions

In this study, structural and optoelectronic properties and photodedection characteristics of diodes constructed from p-zinc telluride (ZnTe) thin film/n-silicon (Si) nanowire heterojunctions are reported. Dense arrays of vertically aligned Si nanowires were successfully synthesized on (1 1 0)-oriented n-type single crystalline Si wafer using simple and inexpensive metal-assisted etching (MAE) process. Following the nanowire synthesis, p-type ZnTe thin films were deposited onto vertically oriented Si nanowires via radio frequency magnetron sputtering to form three-dimensional heterojunctions. A comparative study of the structural results obtained from X-ray diffraction and Raman spectroscopy measurements showed the improved crystallinity of the ZnTe thin films deposited onto the Si nanowire arrays. The fabricated nanowire-based heterojunction devices exhibited remarkable diode characteristics and enhanced optoelectronic properties and photosensitivity in comparison to the planar reference. The electrical measurements revealed that the diodes with nanowires had a well-defined rectifying behaviour with a rectification ratio of 104 at ±2 V and a relatively small ideality factor of n = 1.8 with lower reverse leakage current and series resistance at room temperature in dark condition. Moreover, an open-circuit voltage of 100 mV was also observed under illumination. Based on spectral photoresponsivity measurements, the nanowire-based device exhibited a distinct responsivity and high detectivity in visible and near-infrared (NIR) wavelength regions. The device characteristics observed here offer that the fabricated ZnTe thin film/Si nanowire-based p–n heterojunction structures will find important applications in future and will be a promising candidate for high-performance and low-cost optoelectronic device applications, NIR photodedectors in particular.

Effect of dimethyl sulfoxide on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes

Effect of dimethyl sulfoxide (DMSO) on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes has been studied. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was deposited on n-type Si wafer using facile process of spin coating. The DMSO content was varied from 0 to 8 vol%. Electrical characterization of these heterojunction diodes as performed using both current–voltage (I–V) and capacitance–voltage (C–V) measurements. All diodes showed rectifying behavior. AFM measurement revealed that the surface became more rough after the DMSO treatment of PEDOT:PSS films. The RMS values were found in the range of 4–6 nm. The resistivity of the PEDOT:PSS films decreased with increase in temperature. The addition of DMSO into PEDOT:PSS solution results in a decrease in resistivity of films by approximately two orders of magnitude. PEDOT:PSS films showed high transmission more than 85% in the entire visible region. Raman spectroscopy indicated effect of the DMSO treatment on the chemical structure of PEDOT chains, suggesting a conformational change of PEDOT chain in the film. An optimal value of DMSO was obtained with 5 vol% content, and it showed the best PEDOT:PSS films properties and good quality heterojunction diodes characteristics with ideality factor of 2.4 and barrier height 0.80 eV.

Si nanoparticles embedded in pseudo binaries alloys with AI2O3

The present paper reports the incorporation of Si nanoparticles (NPs) in (Al2O3)x (B2O3)1-x films. A new approach for involving Si NPs (20 nm) p+ doped into sol solution was used. After spin coating deposition and additional annealing at 850°C, (Al2O3)x (B2O3)1-x films with Si NPs have been obtained with thickness of 75 and 120 nm. The (Al2O3)x (B2O3)1-x films were deposited on p-type and n-type Si wafers. The optical study reveals that Si NPs embedded in (Al2O3)x(B2O3)1-x leads to higher absorption in the visible spectral range compared to dielectric layer without nanoparticles. AFM studies show that the incorporated Si nanoparticles into the dielectric layer have probably a uniform distribution on film surface. This conclusion is confirmed by SEM observation. The current - voltage (I-V) characteristics of a structure (Al2O3)x(B2O3)1-x layer with Si NPs on p- type Si shows an ohmic type of conductivity. The sheet resistance is 480 Ohm/sq respectively, when the same layer is deposited on quartz substrate. This work presents a new technological approach for integration of Si NPs in dielectric matrix of (Al2O3)x (B2O3)1-x. The results can find applications for formation of ultra thin emitter for photodiodes and Si solar cells.

Low surface recombination velocity in n-Si passivated by catalytic-chemical vapor deposited alumina films

The surface recombination velocity (S0) in n-type Si (n-Si) wafers has been reduced below 0.1cm/s by dint of positive fixed charges created by alumina (AlOx) films deposited at a film-temperature of 230°C by catalytic chemical vapor deposition (Cat-CVD) using trimethyl aluminum (TMA) and O2. Positive fixed charges of the order of 1012charges/cm2 can be created in AlOx films deposited under O2/TMA flow-rate ratios in the range of 3.5–6.5. The extremely small S0 has been confirmed to be obtainable mainly due to a band bending effect brought about by the positive charges. The polarity and amount of the fixed charges can be determined by the flow-rate ratio of O2/TMA.

Effect of Hydration Property of Pore Wall on Performance of Electric Double Layer Capacitors

Electric Double Layer Capacitors (EDLCs) store charges (ions) on electrode-electrolyte interfaces. When using nanoporous electrodes for EDLCs, specific capacitances decrease as the pore size becomes small due to the difficulty in supply of ions from bulk solution into nanopores. In the course of studies in electrodeposition within nanoporous electrodes, we have revealed that metal ions with a relatively large diameter strongly enhance the electrodeposition within hydrophobic nanopores when the solvent of the deposition bath is water [1]. This result indicates that the ion penetration into the pores is enhanced. We have also reported that by choosing an appropriate combination in hydration property of pore wall and ions, a transition phenomenon occurs within nanopores, which results in a high concentration of metal ions compared with the bulk solution [2]. The results reported in the previous studies lead to an idea that the similar enhancement of ion penetration into nanopores is advantageous for further developments of EDLCs using nanoporous electrodes. In this paper, we focus on the effect of hydration property of pore walls on the capacitances with mesoporous silicon electrodes. Secondly, the effect of pore size on the capacitance is discussed. In the present study, mesoporous silicon is utilized as a model electrode. Mesoporous silicon electrodes were prepared by anodization of an n-type Si (100) wafer with a resistivity of less than 0.02 Ω cm in 22 wt% HF solution. After anodization, the electrode was immersed in n-hexane containing propiolic acid or methyl propiolate to make the surfaces hydrophilic and hydrophobic, respectively [3]. Note that we adopted these organic solutes because they have almost the same molecular structure and show opposite hydration properties, i.e., hydrophilic and hydrophobic. Significant differences in pore size are not expected before and after the modification. An aqueous solution containing 0.1 M tetraethylammonium perchlorate was used for the measurement of EDLCs. Cyclic voltammograms (CVs) were measured using the hydrophilic and hydrophobic porous electrodes at a scan rate of 20 mV s–1. The porous silicon electrodes are oxidized above –0.3 V vs. SHE, so that CVs were measured between –0.5 V and –0.3 V. It should be noted that current density in the present study is calculated based on the projected area (0.785 cm2). A clear difference in hydration property of pore wall is observed in Figure 1. The hydrophobic porous electrode yields a much greater capacitance, meaning that more ions were adsorbed (stored) on the hydrophobic electrode-electrolyte interface. This result suggests that the surface hydration property has an important role on the capacitance of the EDLCs. Reference [1] K. Fukami, R. Koda, T. Sakka, T. Urata, K. Aomoto, H. Takada, M. Nakamura, Y. Ogata, and M. Kinoshita, Chem. Phys. Lett., 542, 99 (2012).[2] K. Fukami, R. Koda, T. Sakka, Y. Ogata, and M. Kinoshita, J. Chem. Phys., 138, 094702 (2013).[3] A. Imanishi, S. Yamane, and Y. Nakato, Langmuir, 24, 10755 (2008).

Blue photoluminescence from nanocrystalline porous silicon structure fabricated by high-current pulsed electron beam irradiation

N-type Si (111) wafers have been processed by high-current pulsed electron beam (HCPEB) treatment with an increasing number of irradiation (1, 10 and 20 pulses). The results of this work show that a highly porous nanostructure was formed after irradiation. Moreover, the high-density Si nanocrystals (Si-ncs) about 3 nm were distributed on the surface of Si wafers and exhibited 3.02 eV Photoluminescence (PL) emission in blue band. The PL intensity increases with the increase in the Si-ncs’ density in accordance with the quantum confinement model, which can be ascribed to the different pulse time of HCPEB treatment. The possible formation mechanisms of micropores and Si-ncs are discussed.

Electrochemical formation of a novel porous silicon/polypyrrole hybrid structure with enhanced electrical and optical characteristics

The electrochemical formation of a hybrid structure composed of a redox-active polypyrrole (PPy) and porous silicon (PSi) layer is demonstrated. PSi layers with pore sizes (∼200nm) are prepared by the electrochemical anodization of n-type Si wafer in HF-based solution, whereas the PPy as a p-type conducting polymer was prepared by electro-oxidative polymerization of parent monomers in acetonitrile solution using PSi as a working electrode. Uniform and vertically-oriented PPy nanorod arrays were successfully fabricated inside the porous matrix. After pore filling, the electrical conductivity and photoluminescence of as-fabricated hybrid structure were remarkably enhanced. The PSi/PPy heterojunction was fully characterized by a variety of techniques including field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. Thermal properties were also evaluated using thermo-gravimetric analysis (TGA) measurements. Formation mechanism and surface properties of such hybrid structure along with its electrical and optical characteristics are addressed and thoroughly discussed.

Characterization of Al/Si junctions on Si(100) wafers with chemical vapor deposition-based sulfur passivation

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky barriers are characterized with current–voltage (I–V), capacitance–voltage (C–V) and activation-energy methods. Al/S-passivated n-type Si(100) junctions exhibit ohmic behavior with a barrier height of <0.078 eV by the I–V method and significantly lower than 0.08 eV by the activation-energy method. For Al/S-passivated p-type Si(100) junctions, the barrier height is ~0.77 eV by I–V and activation-energy methods and 1.14 eV by the C–V method. The discrepancy between C–V and other methods is explained by image force-induced barrier lowering and edge-leakage current. The I–V behavior of an Al/S-passivated p-type Si(100) junction remains largely unchanged after 300 °C annealing in air. It is also discovered that heating the S-passivated Si(100) wafer before Al deposition significantly improves the thermal stability of an Al/S-passivated n-type Si(100) junction to 500 °C.

Multifractal analysis of textured silicon surfaces

Pyramidal textures with random distribution of texture shapes on crystalline Si wafers substantially reduce reflection losses of substrates for high-efficiency solar cells, detectors and similar applications. In this work random pyramids on n-type Si wafers were prepared by anisotropic surface etching in potassium hydroxide (KOH) solution. The morphology of pyramidal shapes was examined by the AFM method and reveals high complexity of the surface structure. Properties of AFM observed pyramidal textures were characterized by the statistical and multifractal methods. This approach provides good platform for the distinguishing between fine details in the pyramidal distributions. Significant correlation between the fractal properties of surface texture and its optical properties characterized by the spectral reflectance function is observed.

Synthesis of Ge nanostructures on Si substrate by a convenient electrochemical technique at room temperature for different durations

The electrochemical deposition technique at room temperature was used to study the synthesis of Ge like-cubic nanorods grown on n-type Si (100) wafer. The effect of deposition time on the morphological, structural and optical properties of nanostructures was investigated. Different Ge morphologies of as-grown on Si were shown by FESEM images. The shape and the dimensions of the structures showed dependence on the deposition time and the film thickness increases with increasing the deposition time. The lattice constants, crystallite size of c-Ge crystal and the strains were calculated. The Raman spectra exhibited slightly downward sift and broader band width in comparison with the bulk-Ge.

Doping-concentration dependence of a boron-doped p-type Ge layer grown on a Si (100) substrates by using RTCVD

Boron-doped p-type Ge layers were grown on n-type Si (100) wafers at various boron doping concentrations by using Rapid Thermal Chemical Vapor Deposition. The root-mean-square was surface roughness of p-type Ge layer increase from 0.708 nm to 19.980 nm as the doping concentrations increase from 3 × 1016 cm−3 to 4 × 1022 cm−3. From High Resolution X-ray diffraction, the in-plane lattice constants and tensile strains of the p-type Ge layer were evaluated as function of boron doping concentration the Raman shift of the for each location indicate a tensile strain from the p-type Ge layer. The tensile strain of the p-type Ge layer decreases from 0.071% to 0.032% as the boron doping concentrations increases from 3 × 1016 cm−3 to 4 × 1022 cm−3. Moreover, the photocurrent peak energies increased. The temperature dependence of the direct band-gap energy, E, of the p-type Ge layer could be described by using Varshnis empirical expression: EΓ(T) = 0.86 − 5.82 × 10−4 T2/(T + 296).

Surface nanostructures on low energy Zn ion implanted crystalline Si and their thermal evolution at different atmospheres

Cz n-type Si (100) wafers were implanted with 45keV Zn ions at a fluence of 1.0×1017ions/cm2. Formation of surface nanostructures, their structures and thermal evolution in different atmospheres have been studied. Our results clearly show that creation of surface nanostructures depends strongly on both annealing temperature and atmosphere. In nitrogen ambient, hemispherical nano-sized bumps could be effectively observed on the Zn-implanted Si surface after annealing at 600°C, and their sizes increase with the annealing temperature up to 800°C. However, in the oxygen ambient, hemispherical nano-sized bumps created at 600°C could be transferred to winding patterns after 800°C annealing. The results from X-ray photoelectron spectroscopy and grazing X-ray diffraction measurements reveal production of Zn NPs near the Si surface in as-implanted state. The thermal growth and transformation of such NPs during annealing contribute to formation and evolution of the observed surface nanostructures.

Structural and Magnetic Properties of Electrodeposited NiFe Alloy on Silicon Nanowires

Perpendicular Silicon nanowires (SiNWs), having 20 micrometer in length, were fabricated by metal assisted chemical etching of n-type Si(100) wafers in aqueous HF-solution. In a second step, NiFe films were electrodeposited onto theses SiNWs. The structure and magnetic properties of as deposited NiFe layers were studied by X ray diffraction (XRD) and vibrating sample magnetometer (VSM). From X-ray diffraction, the FCC NiFe structure was evidenced with a lattice constant, a, equal to 3.5270 (...)

Efficiency Improvement of HIT Solar Cells on p-Type Si Wafers.

Single crystal silicon solar cells are still predominant in the market due to the abundance of silicon on earth and their acceptable efficiency. Different solar-cell structures of single crystalline Si have been investigated to boost efficiency; the heterojunction with intrinsic thin layer (HIT) structure is currently the leading technology. The record efficiency values of state-of-the art HIT solar cells have always been based on n-type single-crystalline Si wafers. Improving the efficiency of cells based on p-type single-crystalline Si wafers could provide broader options for the development of HIT solar cells. In this study, we varied the thickness of intrinsic hydrogenated amorphous Si layer to improve the efficiency of HIT solar cells on p-type Si wafers.

Electric Current Dependence of a Self-Cooling Device Consisting of Silicon Wafers Connected to a Power MOSFET

A self-cooling device has been developed by combining a commercial n-channel power metal–oxide–semiconductor field-effect transistor (MOSFET) and single-crystalline Sb-doped n-type or B-doped p-type silicon wafers in order to improve the heat removal or cooling quantitatively. The electric current dependence of the temperature distribution in the self-cooling device and the voltage between the source and drain electrodes have been measured to estimate the Peltier heat flux. We found that the average temperature is decreased for a power MOSFET in which an electric current of 50 A flows. In particular, the average temperature of the power MOSFET was decreased by 2.7°C with the n-type Si wafer and by 3.5°C with the p-type Si wafer, although an electric current of 40 A makes little difference. This certainly warrants further work with improved measurement conditions. Nonetheless, the results strongly indicate that such n-type or p-type silicon wafers are candidate materials for use in self-cooling devices.