Boron-doped Films Research Articles

Mechanical properties of thin films of hydrogenated silicon and their relationship with microstructure

Thin films of hydrogenated silicon were deposited on glass and single-crystalline silicon substrates using a capacitively coupled radio-frequency plasma-enhanced vapor-deposition system with the help of direct-current bias stimulation. Micro-Raman scattering was applied to investigate the microstructure of the thin films obtained. The crystalline volume fraction, X c, was obtained from the Raman spectra. Microscopic mechanical characterization of the thin films was carried out by nanoindentation based on the conventional depth-sensing indentation method. An analytical relation between X c and the elastic modulus was thereby established. The elastic modulus of the film on a glass substrate was found to be lower than that of the film on a monocrystalline silicon substrate with the same X c. The grain size of a phosphorus-doped thin film was smaller than that of the intrinsic one, with greater ordering of the grains and X c was found to be usually above 40%. A film with boron doping was on the opposite side, with X c usually below 40%. In the phosphorus-doped, intrinsic, and boron-doped films, the elastic moduli were lower when the X c values were 45%, 30%, and 15%, respectively.

Boron-doped nanocrystalline silicon thin films for solar cells

This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 °C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si:H were obtained from transmission and reflection spectra. By employing p + nc-Si:H as a window layer combined with a p′ a-SiC buffer layer, a-Si:H-based p– p′– i– n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current–voltage and spectral-response measurements.

Boron-doped transparent conducting nanodiamond films

Boron-doped nanodiamond (ND) films on silica substrates have been obtained by the method of microwave plasma-enhanced chemical vapor deposition (MWPECVD). Using special technological regimes ensuring the growth of boron-doped ND films after the deposition of an initial ND nucleation layer with small roughness ( 1010 cm−2), it is possible to obtain conducting ND films transparent in the UV spectral range. Dependence of the transparency and conductivity of the obtained films on the boron concentration and methane content in the working methane-hydrogen mixture has been studied.

Study of the Electrical and Optical Properties of the Silicon Carbide Thin Film

Using the technology of Plasma Enhanced Chemical Vapor Deposition (PECVD), the boron-doped SiC thin films were prepared with the gas of SiH4,CH4, H2 and B2H6, the effects were investigated on the electrical and optical properties of the film caused by varying the carbon content and the concentration of boron doping. The results showed that when the flow ratio of CH4/SiH4 ranged from 0.3 to 0.4 and the flow ratio of B2H6/SiH4 ranged from 0 to 0.1, the optical band gap of the film was above 2.2eV, and the electrical conductivity was above 1×10-7 S/cm. The parameters of the ranges met the requirements on the aspects of electrical and optical properties as window layer for the solar cell.

On-Chip Integration of Acceleration, Pressure, and Temperature Composite Sensor With a Single-Sided Micromachining Technique

Abstract-This paper presents a novel composite sensor that is monolithically integrated with an accelerometer, a pressure sensor, and a thermometer by using a single-side-processed micromachining technique. Such composite sensors are highly demanded in tire pressure monitoring system (TPMS) applications. Based on heat convection, the accelerometer consists of a microheater and a pair of detector to measure the acceleration-induced temperature distribution change. Thermopile- and thermistor-based detectors both have been used to measure the temperature distribution change. Under a heating power of 10.9, 19.4, and 30.3 mW, the sensitivity of the thermopile-based accelerometer is measured as 37.92, 85.04, and 134.08 μV/g, respectively (while the thermistor based accelerometer shows a sensitivity of 25.96, 55.79, and 86.67 μV/g). The two detecting methods both feature enough frequency range that is higher than 100 Hz. In the pressure sensor, the low-stress silicon nitride diaphragm is designed into a narrow rectangular shape, on which four polysilicon piezoresistors are configured into a Wheatstone bridge. The sensitivity of the 450-KPa-ranged pressure sensor is measured as 45.9 mV/3 V FS, the nonlinearity is ±0.84% FS, and the over-range capability is ten times the measured range. The tire temperature monitoring thermometer is also made up of polysilicon and is measured with a linear resistance change versus temperature over the range of -40 °C-+100 °C. In the on-chip integrated sensors, a low-stress silicon nitride thin film is used as the electric isolation layer, the pressure diaphragm, and the heating-insulating freestanding beams. The boron-doped polysilicon film is used as the piezoresis tors, the heater, the thermopile, and the thermometer. After wafer level packaging with an aligned adhesive bonding technique, the 2.5 × 2.5 × 0.84 mm3 microsensor chips are promising for TPMS low-cost fabrication and volume applications.

Electrochemical performances of B doped and undoped diamond-like carbon (DLC) films deposited by femtosecond pulsed laser ablation for heavy metal detection using square wave anodic stripping voltammetric (SWASV) technique

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets. In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd 2+, Pb 2+, Ni 2+ and Hg 2+, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at −1.3 V deposition potential, and 90 s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si 3N 4 electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 μg/L or 2 μg/L and a dynamic range from 1 or 2 to 25 μg/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 μA/ppb or μA μg −1 L for Cd 2+, Pb 2+, Ni 2+ and Hg 2+, respectively.

Improvements in the formation of boron-doped diamond coatings on platinum wires using the novel nucleation process (NNP)

In order to increase the initial nucleation density for the growth of boron-doped diamond on platinum wires, we employed the novel nucleation process (NNP) originally developed by Rotter et al. [1]. This pretreatment method involves (i) the initial formation of a thin carbon layer over the substrate followed by (ii) ultrasonic seeding of this “soft” carbon layer with nanoscale particles of diamond. This two-step pretreatment is followed by the deposition of boron-doped diamond by microwave plasma-assisted CVD. Both the diamond seed particles and sites on the carbon layer itself function as the initial nucleation zones for diamond growth from an H 2-rich source gas mixture. We report herein on the characterization of the pre-growth carbon layer formed on Pt as well as boron-doped films grown for 2, 4 and 6 h post NNP pretreatment. Results from scanning electron microscopy, Raman spectroscopy and electrochemical studies are reported. The NNP method increases the initial nucleation density on Pt and leads to the formation of a continuous diamond film in a shorter deposition time than is typical for wires pretreated by conventional ultrasonic seeding. The results indicate that the pre-growth layer itself consists of nanoscopic domains of diamond and functions well to enhance the initial nucleation of diamond without any diamond powder seeding.

Local Density Diffusivity (LDD-) Model for Boron Out-Diffusion of <i>In Situ</i> Boron-Doped Si<sub>0.75</sub>Ge<sub>0.25</sub> Epitaxial Films Post Advanced Rapid Thermal Anneals with Carbon Co-Implant

Boron in silicon has presented challenges for decades because of clustering and so-called transient enhanced diffusion [1-2]. An understanding of boron diffusion post rapid thermal annealing in general, and out of in situ doped epitaxially grown silicon-germanium films in particular, is essential to hetero junction engineering in microelectronic device technology today. In order to model boron diffusion, post-implantation, the local density diffusion (LDD) model has been applied in the past [3]. Via mathematical convolution of the diffusion model slope and the initial boron concentration profile, these former results were transferred to this work. In this way, non-diffusing boron was predicted to exist in the center of the presented in situ boron-doped films. In addition, boron diffusion control by co-implanted carbon was demonstrated and the applied LDD model was completed and confirmed by adapting A. Einstein’s proof [4] for this purpose.

The Superconducting Transition in Boron Doped Silicon Films

We report on a detailed analysis of the superconducting properties of boron-doped silicon films grown along the 001 direction by gas immersion laser doping. This technique is proved to be a powerful technique to dope silicon in the alloying range 2-10 at.% where superconductivity occurs. The superconducting transitions are sharp and well defined both in resistivity and magnetic susceptibility. The variation of Tc on the boron concentration is in contradiction with a classical exponential dependence on superconducting parameters. Electrical measurements were performed in magnetic field on the sample with cB = 8 at.% (400 laser shots) which has the highest Tc (0.6 K). No hysteresis was found for the transitions in magnetic field, which is characteristic of a type-II superconductor. The corresponding upper critical field was on the order of 1000 G at low temperatures, much smaller than the value previously reported. The temperature dependence of Hc2 is very well reproduced by the linearized Gorkov equations neglecting spin effects in the very dirty limit. These measurements in magnetic field allow an estimation of the electronic mean-free path, the coherence length, and the London penetration depth within a simple two-band free electron model.

ChemInform Abstract: Solution-Grown Cadmium Sulfide Films for Photovoltaic Devices.

This paper reports on thin films of cadmium sulfide (CdS) which have major applications in optoelectronic devices. Several techniques have been developed for the deposition of CdS films. Among these, growth of CdS films from an aqueous solution is the low-cost technique suitable for many applications. In this work, the deposition of device quality CdS films on glass and SnO[sub 2]:F/glass substrates from an aqueous solution containing cadmium acetate, ammonia, ammonium acetate, and thiourea has been investigated. The structural and electrical properties of CdS films have been characterized. The doping of CdS films with boron and the properties of boron-doped CdS films have also been studied. High efficiency thin film CdS/CdTe solar cells have been prepared from solution-grown CdS films.

Effect of nitrogen on deposition and field emission properties of boron-doped micro- and nano-crystalline diamond films

Abstract In this paper, we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition. The diamond films consisting of micro-grains (nano-grains) were realized with low (high) boron source flow rate during the growth processes. The transition of micro-grains to nano-grains is speculated to be strongly (weekly) related with the boron (nitrogen) flow rate. The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate. The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples, which are related to the combined phase composition, boron doping level and texture structure. There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.

Electrical properties and far infrared optical conductivity of boron-doped single-walledcarbon nanotube films

Here we report a new approach for producing clean and homogeneous boron-dopedsingle-walled carbon nanotubes. This approach combines the homogeneous dispersion ofBnOm + ionic molecules over the nanotube surfaces in a liquid solution, with a hightemperature chemical reaction that incorporates the boron atoms into thesp2 carbon network of the nanotube wall. A comparative study of sheet resistance versusoptical transmission in nanotube network films with and without boron-doping is alsopresented. Although electron energy loss spectroscopy revealed very low B-doping levels (<1 at.%), the dc conductivity of doped samples was raised by a factor of 3.4. Changes in the freecarrier contribution to the optical conductivity of single-walled carbon nanotube (SWCNT) filmsinduced by boron-doping was also studied via optical transmission in the far-infrared (IR) (50–7000 cm − 1). A Drude model was fitted to the changes in the far-IR conductivity to quantify theadditional free carrier concentration induced by the B-doping.

Plasma Processing of Boron-Doped Nano-Crystalline Diamond Thin Film Fabricated on Poly-Crystalline Diamond Thick Film

Plasma treatments of boron-doped nano-crystalline diamond (NCD) thin films were carried out in order to improve their electrical properties of the films. Boron-doped NCD thin films were fabricated on well polished poly-crystalline diamond (PCD) thick films in a microwave plasma enhanced chemical vapor deposition (MPCVD) reactor, then they were processed in methane, argon, hydrogen and B2H6 (0.1% diluted by H2) plasmas, respectively. Scanning electron microscopy (SEM) and atomic force microscope (AFM) results show that the surface morphology changed little during the 10 min treatment. Secondary ion mass spectroscopy (SIMS) results indicate that B2H6 plasma was efficient for increasing boron concentration in NCD films, while the carrier analyses demonstrates that CH4 plasma processing was effective to activate the dopants and resulted in good electrical properties.

Giant electric double-layer capacitance of heavily boron-doped diamond electrode

The physical and electrochemical properties of boron-doped polycrystalline diamond electrodes, prepared with various B/C ratio, i.e., 0.1%, 0.5% (BDD-A), 1% (BDD-B), and 5% (BDD-C), were investigated. Electrochemical measurements of the heavily boron-doped films (BDD-C) showed giant electric double-layer capacitance and activity which is significantly larger than BDD-A and BDD-B as well as glassy carbon electrodes. However, interestingly, actual boron concentration of BDD-C was observed to be almost the same as that of BDD-B by secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES) analysis. It is suggested that the large capacitance is due to a few sp 2-bonded carbon impurities, which was observed only in BDD-C, although the amount of the sp 2-bonded nondiamond species are very small. In the present work, the reason for the interesting electrochemical properties of heavily boron-doped diamond electrodes is discussed. Furthermore, dimensional stability of the electrodes was also confirmed by conducting harsh anodic treatment.

Study of Boron-Doped ZnO Transparent Conductive Thin Films

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Distribution in angular mismatch between crystallites in diamond films grown in microwave plasma

High resolution electron backscattered diffraction (EBSD) has been used for analysis of grain size, texture and stress distribution on growth side of free-standing polycrystalline diamond films of different grade. The undoped and moderate boron-doped films of 0.3–0.5 mm thickness were grown by microwave plasma CVD. The highest number of stressed domains, mostly located at grain boundaries, and the largest average grain misorientation angle ( θ ≈ 6°) have been found for B-doped film. Highly defected and highly [001] oriented “black” diamond exhibited much more rear stress domains, this being ascribed to angular mismatch as small as θ = 0.5° in that film. The samples of “white” diamond showed somewhat intermediate pictures, with stress observed both in bulk and on grain boundaries. Evolution of texture (columnar growth) and stress distribution with film thickness has been observed with EBSD study of film cross-sections.

Inductively coupled plasma-assisted RF magnetron sputtering deposition of boron-doped microcrystalline Si films

An innovative custom-designed inductively coupled plasma-assisted RF magnetron sputtering deposition system has been developed to synthesize B-doped microcrystalline silicon thin films using a pure boron sputtering target in a reactive silane and argon gas mixture. Films were deposited using different boron target powers ranging from 0 to 350 W at a substrate temperature of 250 °C. The effect of the boron target power on the structural and electrical properties of the synthesized films was extensively investigated using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and Hall-effect system. It is shown that, with an initial increase of the boron target power from 0 to 300 W, the structural and electrical properties of the B-doped microcrystalline films are improved. However, when the target power is increased too much (e.g. to 350 W), these properties become slightly worse. The variation of the structural and electrical properties of the synthesized B-doped microcrystalline thin films is related to the incorporation of boron atoms during the crystallization and doping of silicon in the inductively coupled plasma-based process. This work is particularly relevant to the microcrystalline silicon-based p– i– n junction solar cells.

Low-temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers

We report on a detailed analysis of the superconducting properties of boron-doped silicon films grown along the 001 direction by Gas Immersion Laser Doping. The doping concentration cB has been varied up to approx. 10 at.% by increasing the number of laser shots to 500. No superconductivity could be observed down to 40mK for doping level below 2.5 at.%. The critical temperature Tc then increased steeply to reach 0.6K for cB = 8 at%. No hysteresis was found for the transitions in magnetic field, which is characteristic of a type II superconductor. The corresponding upper critical field Hc2(0) was on the order of 1000 G, much smaller than the value previously reported by Bustarret et al. in Nature (London) 444, 465 (2006).

Improvement of PECVD Silicon–Germanium Crystallization for CMOS Compatible MEMS Applications

This paper investigates the influence of the electrode spacing, chamber pressure, total gas flow, and dilution on the crystallinity, resistivity, uniformity, and stress of polycrystalline silicon–germanium (poly-SiGe) films grown by plasma-enhanced chemical vapor deposition (PECVD). Boron-doped PECVD SiGe films of thick are deposited on chemical vapor deposition layers from , , and precursors. The microstructure is verified by transmission electron microscopy and by X-ray diffraction. It was discovered that for constant temperature and deposition rate, the PECVD SiGe microstructure changes from completely amorphous to polycrystalline by increasing the electrode spacing and pressure due to reduced ion bombardment. A process window of an electrode spacing and pressure for the PECVD poly-SiGe deposition is thus identified based on a sheet resistance mapping method. Increasing the total gas flow dramatically improves the within-wafer crystallinity variation and further reduces the resistivity. Increasing the flow during PECVD shifts the stress from and further reduces the crystallinity variation over the wafer. In addition, the effect of changing the to ratio and the in situ boron doping by adding is also investigated. The findings in this paper are expected to facilitate the use of poly-SiGe in the above complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) applications.

Semiconducting to metallic-like boron doping of nanocrystalline diamond films and its effect on osteoblastic cells

The impact of boron doping level of nanocrystalline diamond (NCD) films on the character of cell growth (i.e., adhesion, proliferation and differentiation) is presented. Intrinsic and boron-doped NCD films were grown on Si/SiO 2 substrates by microwave plasma CVD process. The boron-doped samples were grown by adding trimethylboron (TMB) to the gas mixture of methane and hydrogen. Highly resistive (0 ppm), semiconducting (133 or 1000 ppm), and metallic-like (6700 ppm) NCD films were tested as the artificial substrates for the cultivation of osteoblast-like MG 63 cells. The conductivity and surface charge increased monotonically with the increasing boron content. All NCD substrates showed good biocompatibility and stimulated the adhesion and growth of MG 63 cells. Higher osteocalcin concentration (by more than 30%) for the cells growing on 1000 and 6700 ppm boron-doped NCD films was found which indicates an enhancement in the cell growth biochemistry.