Crystal Wafers Research Articles

The space charge limited current and huge linear magnetoresistance in silicon

Huge magnetoresistance in space charge regime attracts broad interest on non-equilibrium carrier transport under high electric field. However, the accurate fitting for the current-voltage curves from Ohmic to space charge regime under magnetic fields has not been achieved quantitatively. We conjecture that the localized intensive charge dynamic should be taken into consideration. Here, by introducing a field-dependent dielectric constant, for the first time, we successfully simulate the current-voltage curves of covalent crystal silicon wafers under different magnetic fields (0–1 Tesla). The simulation reveals that the optical phonon, instead of the acoustic phonon, plays a major role for the carriers transport under magnetic fields in space charge regime.

Laser drilling of micro-holes in single crystal silicon, indium phosphide and indium antimonide using a continuous wave (CW) 1070 nm fibre laser with millisecond pulse widths

The laser micro-drilling of “thru” holes, also known as via holes, in Si, InP and InSb semiconductor wafers was studied using millisecond pulse lengths from an IPG Laser Model YLR-2000 CW multimode 2 kW Ytterbium Fibre Laser and a JK400 (400 W) fibre laser, both with 1070 nm wavelength. The flexibility of this laser wavelength and simple pulsing scheme were demonstrated for semiconductor substrates of narrow (InSb Eg 0.17 eV) and wide (InP Eg 1.35 eV)) room-temperature bandgap, Eg, with respect to the photon energy of 1.1 eV. Optical microscopy and cross-sectional analysis were used to quantify hole dimensions and the distribution of recast material for all wafers and, for silicon, any microcracking for both (100) and (111) single crystal surface Si wafer orientations. It was found that the thermal diffusivity was not a sufficient parameter for predicting the relative hole sizes for the Si, InP and InSb single crystal semiconductors studied. Detailed observations for Si showed that, between the threshold energies for surface melting and the irradiance for drilling a “thru” hole from the front surface to rear surface, there was a range of irradiances for which micro-cracking occurred near the hole circumference. The directionality and lengths of these microcracks were studied for the (100) and (111) orientations and possible mechanisms for formation were discussed, including the Griffith criterion for microcracks and the failure mechanism of fatigue usually applied to welding of metals. For Si, above the irradiance for formation of a thru-hole, few cracks were observed. Future work will compare similar observations and measurements in other narrow- and wide-bandgap semiconductor wafer substrates. We demonstrated one application of this laser micro-drilling process for the micro-fabrication of a thru hole precisely-located in the centre of a silicon-based atom chip which had been patterned using semiconductor lithographic techniques. The end-user application was a source of magneto-optically trapped (MOT) cold atoms of Rubidium (87Rb) for portable quantum sensing.

Stress damage process of silicon wafer under millisecond laser irradiation

The stress damage process of a single crystal silicon wafer under millisecond laser irradiation is studied by experiments and numerical simulations. The formation process of low-quality surface is monitored in real-time. Stress damage can be observed both in laser-on and -off periods. Plastic deformation is responsible for the first stress damage in the laser-on period. The second stress damage in the laser-off period is a combination of plastic deformation and fracture, where the fundamental cause lies in the residual molten silicon in the ablation hole.

Facile synthesis and fabrication of a poly(ortho-anthranilic acid) emeraldine salt thin film for solar cell applications

Schematic diagram of the Au/PANA-ES/p-Si/Al heterojunction device.

Measurement of surface profile and thickness of multilayer wafer using wavelength-tuning fringe analysis

Wavelength-tuning interferometry has been widely used to measure and estimate the surface profile of optical components. However, in multilayer interferometry, the coupling error between the higher harmonics and the phase-shift error causes a considerable systematic error in the calculated phase. In this research, the new 7N − 6 phase-shifting algorithm was developed using the characteristic polynomial theory. The coupling errors calculated by various types of phase-shifting algorithms were analyzed. The surface profile and optical thickness deviation of the lithium niobate crystal wafer were measured simultaneously using wavelength-tuning Fizeau interferometry and the 7N − 6 algorithm. The experimental results were compared in terms of observed ripples and measurement repeatability.

Detection of Cadmium Ion in Potable Water Using Quartz Crystal Microbalance

The presence of heavy metal e.g. cadmium in potable water is one of the major threats on our health. It should be detected and removed from potable water before consumption. The maximum permissible concentration of cadmium ion in drinking water lies in the range of 2–10 ppb. The consumption of excessive cadmium through potable water can lead to cancer, and can affect the organs like kidney and lungs severely. In this article, we report the development of a piezoelectric based sensor for the detection of cadmium ion in water. A functional layer of nanocomposite of single walled carbon nanotubes and beewax was deposited by spin coating technique onto 5 MHz AT‐cut quartz crystal wafers and the shift in resonance due to physioadsorption of cadmium from water medium was recorded. We find a very stable linear response curve with the lowest detectable concentration of 5.2 ppb. The change in the morphology of the functional layer before and after adsorption of cadmium is studied using atomic force microscope and field emission scanning electron microscope. The presence of calcium ion in water medium affected the response curves of cadmium sensing. We found a systematic variation in sensitivity towards Cd ion due to the presence of Ca ion in water medium.

Recrystallization-Induced Surface Cracks of Carbon Ions Irradiated 6H-SiC after Annealing.

Single crystal 6H-SiC wafers with 4° off-axis [0001] orientation were irradiated with carbon ions and then annealed at 900 °C for different time periods. The microstructure and surface morphology of these samples were investigated by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Ion irradiation induced SiC amorphization, but the surface was smooth and did not have special structures. During the annealing process, the amorphous SiC was recrystallized to form columnar crystals that had a large amount of twin structures. The longer the annealing time was, the greater the amount of recrystallized SiC would be. The recrystallization volume fraction was accorded with the law of the Johnson–Mehl–Avrami equation. The surface morphology consisted of tiny pieces with an average width of approximately 30 nm in the annealed SiC. The volume shrinkage of irradiated SiC layer and the anisotropy of newly born crystals during annealing process produced internal stress and then induced not only a large number of dislocation walls in the non-irradiated layer but also the initiation and propagation of the cracks. The direction of dislocation walls was perpendicular to the growth direction of the columnar crystal. The longer the annealing time was, the larger the length and width of the formed crack would be. A quantitative model of the crack growth was provided to calculate the length and width of the cracks at a given annealing time.

Characterization of a bent Laue double-crystal beam-expanding monochromator.

A bent Laue double-crystal monochromator system has been designed for vertically expanding the X-ray beam at the Canadian Light Source's BioMedical Imaging and Therapy beamlines. Expansion by a factor of 12 has been achieved without deteriorating the transverse coherence of the beam, allowing phase-based imaging techniques to be performed with high flux and a large field of view. However, preliminary studies revealed a lack of uniformity in the beam, presumed to be caused by imperfect bending of the silicon crystal wafers used in the system. Results from finite-element analysis of the system predicted that the second crystal would be most severely affected and has been shown experimentally. It has been determined that the majority of the distortion occurs in the second crystal and is likely caused by an imperfection in the surface of the bending frame. Measurements were then taken to characterize the bending of the crystal using both mechanical and diffraction techniques. In particular, two techniques commonly used to map dislocations in crystal structures have been adapted to map local curvature of the bent crystals. One of these, a variation of Berg-Berrett topography, has been used to quantify the diffraction effects caused by the distortion of the crystal wafer. This technique produces a global mapping of the deviation of the diffraction angle relative to a perfect cylinder. This information is critical for improving bending and measuring tolerances of imperfections by correlating this mapping to areas of missing intensity in the beam.

Statistical and interferometric determination of the optical thickness of a multilayer transparent plate

Wavelength-tuning Fizeau interferometry has been widely used to measure and estimate the optical thickness of optical components. However, in multilayer interferometry, the coupling errors between the higher harmonics and phase-shift error cause systematic errors in the calculated phase distribution. This paper presents the derivation of a 15-sample phase-shifting algorithm that can compensate for the phase-shift miscalibration and up-to-first-order nonlinearity of the coupling errors between the second-order harmonic and phase-shift error. The characteristics of the 15-sample algorithm are estimated with respect to the Fourier representation in the frequency domain. The optical thickness of a highly reflective lithium niobate crystal wafer is measured using a wavelength-tuning Fizeau interferometer and 15-sample algorithm. Finally, the optical thickness is determined from the measured data using the statistical Student’s t test.

Nanowire decorated, ultra-thin, single crystalline silicon for photovoltaic devices

Reducing silicon (Si) wafer thickness in the photovoltaic industry has always been demanded for lowering the overall cost. Further benefits such as short collection lengths and improved open circuit voltages can also be achieved by Si thickness reduction. However, the problem with thin films is poor light absorption. One way to decrease optical losses in photovoltaic devices is to minimize the front side reflection. This approach can be applied to front contacted ultra-thin crystalline Si solar cells to increase the light absorption. In this work, homojunction solar cells were fabricated using ultra-thin and flexible single crystal Si wafers. A metal assisted chemical etching method was used for the nanowire (NW) texturization of ultra-thin Si wafers to compensate weak light absorption. A relative improvement of 56% in the reflectivity was observed for ultra-thin Si wafers with the thickness of 20 ± 0.2 μm upon NW texturization. NW length and top contact optimization resulted in a relative enhancement of 23% ± 5% in photovoltaic conversion efficiency.

New Heterostructures on the Basis of Cd1-xMnxTe Solid Solutions: Photoelectric Properties

The new technology of energy barrier fabrication by thermal treatment of Cd1-xMnxTe solid solution crystal wafers was proposed. By the first time the Ox/Cd1-хMnхTe (х=0.00–0.70) heterostructures with rectifying and photosensitive properties was fabricated. The relative quantum efficiency of photoconversion of fabricated by the firs time heterostructures was investigated. The nature of the interband optical transitions and values of the band gap in Cd1-xMnxTe was determined.

Influence of deposition temperature during LPCVD on surface properties of ultrathin polysilicon films

The selection of the proper materials for the fabrication of the micro electro mechanical systems (MEMS) is a very important issue in the MEMS research. The materials should be adequate for the fabrication process as well as they have to demonstrate in particular good adhesive (to avoid stiction between contacting/sliding components) and frictional/tribological properties. We fabricated ultrathin (50 nm thick) polysilicon films on single crystal silicon wafers at various deposition process conditions and observed the effect of the process parameters on surface topography and adhesive as well as frictional properties of the produced films. The atomic force microscope was used in these studies equipped with special cantilevers. We identified interesting correlations between the process parameters and adhesive/frictional properties of the studied films which enable to optimize the process to decrease adhesion (stiction) and friction between sliding components of MEMS devices and compared them to previous research done at samples with thicker layer. Topography of both samples and cantilevers has been studied in depth to allow later simulation of the interface. Additional measurements of friction in various humidites should be done next in order to assess the influence of its impact on friction coefficient. Further comparison of adhesion to friction in particular environmental properties might also increase our understanding of MEMS surface interactions.

Switchable diode effect in oxygen vacancy-modulated SrTiO3 single crystal

SrTiO3 (STO) single crystal wafer was annealed in vacuum, and co-planar metal–insulator–metal structure of Pt/Ti/STO/Ti/Pt were formed by sputtering Pt/Ti electrodes onto the surface of STO after annealing. The forming-free resistive switching behavior with self-compliance property was observed in the sample. The sample showed switchable diode effect, which is explained by a simple model that redistribution of oxygen vacancies (OVs) under the external electric field results in the formation of n–n+ junction or n+–n junction (n donated n-type semiconductor; n+ donated heavily doped n-type semiconductor). The self-compliance property is also interpreted by the formation of n–n+/n+–n junction caused by the migration of the OVs under the electric field.

Crystal Growth and Linear and Nonlinear Optical Properties of KIO3·Te(OH)6

A single crystal of the nonlinear optical material KIO3·Te(OH)6 (KTI) with dimensions of 37 × 7 × 5 mm3 was successfully grown at room temperature by slow evaporation. Linear and nonlinear optical measurements were performed on these crystals. Rocking curve measurements indicate that the single crystal is of high quality with a full width at half-maximum (fwhm) of 0.023° (82 arcseconds) from the (010) reflection. Refractive index measurements revealed a birefringence of 0.0545 @ 1064 nm. Through the refractive index measurements and the fitted Sellmeier equations, we determined the Type I and Type II phase-matching wavelength ranges. KTI is Type I (Type II) phase-matchable with a fundamental wavelength range from 674–3266 nm (880–2260 nm). Powder second-harmonic generation (SHG) measurements indicate an SHG intensity of 1.2× KH2PO4 (KDP). SHG coefficients were determined by the Maker fringe method on cut and polished (100) and (010) single crystal wafers. The d31 = 0.24 pm/V and d32 = 0.73 pm/V were deter...

Self-compensation in arsenic doping of CdTe

Efficient p-type doping in CdTe has remained a critical challenge for decades, limiting the performance of CdTe-based semiconductor devices. Arsenic is a promising p-type dopant; however, reproducible doping with high concentration is difficult and carrier lifetime is low. We systematically studied defect structures in As-doped CdTe using high-purity single crystal wafers to investigate the mechanisms that limit p-type doping. Two As-doped CdTe with varying acceptor density and two undoped CdTe were grown in Cd-rich and Te-rich environments. The defect structures were investigated by thermoelectric-effect spectroscopy (TEES), and first-principles calculations were used for identifying and assigning the experimentally observed defects. Measurements revealed activation of As is very low in both As-doped samples with very short lifetimes indicating strong compensation and the presence of significant carrier trapping defects. Defect studies suggest two acceptors and one donor level were introduced by As doping with activation energies at ~88 meV, ~293 meV and ~377 meV. In particular, the peak shown at ~162 K in the TEES spectra is very prominent in both As-doped samples, indicating a signature of AX-center donors. The AX-centers are believed to be responsible for most of the compensation because of their low formation energy and very prominent peak intensity in TEES spectra.

Investigation and modelling of hybrid laser-waterjet micromachining of single crystal SiC wafers using response surface methodology

A hybrid laser-waterjet micromachining technology was proposed to implement near damage-free and high-efficient micromachining of thermal-sensitive hard and brittle materials. A new material removal concept was used where a waterjet is applied off-axially to expel the “softened” elemental material by laser radiation and cool the material to eliminate thermal damages during the material removal process. The present study investigates the effect of process parameters and their interaction on the cutting depth, cutting width and the material removal rate in the hybrid laser-waterjet micromachining of single crystal SiC wafers. The analysis of variance (ANOVA) indicates that waterjet inclination angle, waterjet offset distance, nozzle stand-off distance, traverse speed of hybrid cutting head, average laser power and waterjet pressure are the significant terms on cutting depth, cutting width as well as material removal rate. The quadratic backward-eliminated regression models are developed using response surface methodology (RSM). The models show that the material removal ability and the material removal rate increase with the increased average laser power and decrease with the increased nozzle stand-off distance and waterjet pressure. Waterjet offset distance has a knee-point value on the machining results. Cutting depth and width decrease with the increased traverse speed of hybrid cutting head but material removal rate increases with the increased traverse speed when the traverse speed is smaller than a certain value. The turbulent water breaks down the laser optically and weakens its heating ability. The critical waterjet offset distance can also be changed since the interactive effect of the process parameters. The verification results show the models can perform predictions with acceptable errors. Moreover, as compared to laser dry ablation, the photographs of the machined surface and its 3D profile illustrate that hybrid laser-waterjet micromachining can obtain much deeper and wider groove with V-sharp cross-sectional profile. It can significantly reduce or even eliminate thermal damages such as heat-affected zone (HAZ) and re-solidified layer by using the hybrid laser-waterjet micromachining technology.

Formation of cross-cutting structures with different porosity on thick silicon wafers

Three-layered pass-through structures of two types have been obtained on 500μm thick single crystal silicon wafers by electrochemical etching in a 48% solution of hydrofluoric acid without using additional single crystal layer removal operations. The first type of the pass-through structures comprises two outermost 220–247.5μm thick macroporous silicon layers with a pore diameter of 7–10μm and an intermediate 5–60μm thick mesoporous silica layer with a pore diameter of 100–150nm. For the formation of the first type structures we used two-stage etching without cell disassembly:–in a 48% water solution of hydrofluoric acid (H2O: HF = 1: 1 vol.) for 140–180min with a current density of 40mA/cm2;–in a 48% water/alcohol solution of hydrofluoric acid (H2O: HF: С2Н5ОН = 1: 1: 1 vol.) for 60–90min with a current density of 10mA/cm2.The second type pass-through structures include a macroporous silicon layer with a thickness of 250μm which interlock in the depth of the silicon wafer to form a cavity with a size of 4–8μm. For the formation of the second type structures we only used the first one of the abovementioned stages, the etching time being longer, i.e. 210min. All the etching procedures were carried out in a cooling chamber at 5°C. The developed technology will provided for easier and more reliable formation of the monolithic structures of membrane-electrode assembly micro fuel cells.

Plasmonic behavior of III-V semiconductors in far-infrared and terahertz range

BackgroundIn this article, III-V semiconductors are proposed as materials for far-infrared and terahertz plasmonic applications. We suggest criteria to estimate appropriate spectral range for each material including tuning by fine doping and magnetic field.MethodsSeveral single-crystal wafer samples (n,p-doped GaAs, n-doped InP, and n,p-doped and undoped InSb) are characterized using reflectivity measurement and their optical properties are described using the Drude-Lorentz model, including magneto-optical anisotropy.ResultsThe optical parameters of III-V semiconductors are presented. Moreover, strong magnetic modulation of permittivity was demonstrated on the undoped InSb crystal wafer in the terahertz spectral range. Description of this effect is presented and the obtained parameters are compared with a Hall effect measurement.ConclusionAnalyzing the phonon/free carrier contribution to the permittivity of the samples shows their possible use as plasmonic materials; the surface plasmon properties of semiconductors in the THz range resemble those of noble metals in the visible and near infrared range and their properties are tunable by either doping or magnetic field.

Control of optical properties of metal-dielectric planar plasmonic nanostructures by adjusting their architecture in the case of TiAlN/Ag system

The multilayer Ag/(Ti34Al66)N metal-insulator-metal (MIM) heterostructures with different thicknesses of individual layers varied from several to several hundred nanometers were fabricated by DC-magnetron sputtering on the surfaces of Si single crystal wafers. The coatings structure was determined by STEM. The phase composition and crystallography of individual layers were studied by X-ray diffraction. The reflection indexes were measured in the photons energies range from 1 to 5 eV, or from 1240 to 248 nm. The spectroscopy of plasmon losses and plasmon microscopy allowed us to measure the plasmons losses characteristic energies and their surface distribution. The energies of plasmons peaks and their locations are strongly depending on Ag layers thickness in the MIM nanocomposite. The surface plasmon with energy about 4 eV was observed in the middle of 20 nm Ag layer. The plasmons were localized at the metal/dielectric interface for Ag layers 5 nm and less. The reflectance spectral profiles edges positions at long and short waves are correlated with plasmons energies and features of their spatial distribution. The MIMs based on the TiAlN/Ag can find applications as optical filters, photovoltaic energy conversion devices, etc.

Chemical vapor deposition of graphene on insulating substrates and its potential applications

As the first two-dimensional crystal isolated in 2004, graphene has triggered numerous fundamental and technological studies because of its unique properties and a wide range of potential applications. To take these applications to an industrial level requires successful large scale growth of high quality graphene. Among popular methods for graphene synthesis, chemical vapor deposition (CVD) has received a lot of attention because of its relatively high yields, high quality and low cost in preparation of graphene. In addition, CVD is compatible with the existing silicon semiconductor processes, and exhibits potential for synthesis and applications of graphene at industrial scale. CVD graphene has been synthesized on various metal substrates such as ruthenium, iridium, platinum, nickel and copper. Though suitable for mass production, the need to transfer the graphene to different substrates has so far constrained its up-scaling to roll-to-roll production methods. However, CVD graphene on metal need transfer to insulating substrates for further device fabrication and characterization, and the extra transfer step inevitably causes the degradation of the graphene quality because of crack formation or resists residues. Researchers have developed some novel technologies aiming at reducing the influence of transfer process on the quality of graphene, but transfer process is still time-consuming and relatively expensive. An alternative to overcome the transfer difficulty is to synthesize graphene directly on insulating substrates. Epitaxial growth of graphene on single crystal SiC is one route towards mass production of graphene, however, single crystal SiC wafers are still very expensive. The search for better production techniques of graphene, in particular a transfer-free production method of high quality graphene, has intensified over the last few years. An amount of effective strategies have been utilized to realize the direct synthesis of high quality graphene on insulating substrates such as h-BN, silicon oxide, quartz, sapphire, SrTiO3 and even normal glass. Due to the lack of catalytic capability and carbon-dissolving ability in insulating substrates, the direct growth of graphene often associates with the problems of high nucleation density, small domain size, poor layer control and slow growth rate. As such, more research works should be conducted to explore the growth mechanism on the insulating substrates. In this paper, we reviewed recent progresses about direct growth of graphene on insulating substrates by chemical vapor deposition and its electronic applications. Firstly, we briefly discussed the newly progresses of graphene preparation and application. Great progress have been achieved in the field of direct synthesis of graphene on insulating substrates, however, there is still much room to improve further in many aspects, such as quality, domain size, layer and substrate suitability of graphene. We classified the growth strategies on insulating substrates into four groups: non-catalyst assisted method, plasma enhanced method, interface catalyzed growth and metal-vapor assisted growth. In each strategy, details of technology and merits were carefully discussed. In addition, we also introduced the typical applications of each strategy, which exhibits extraordinary prospect for improving our daily life. Finally, we shared our perspective views on future trend of this research field. We believe that with more and more efforts from the graphene-research community, technologies about direct synthesis of graphene on insulating substrates will be developed further. The future of directly grown graphene will become clearer in industrial applications.