Trimethylboron Research Articles

In situ boron doping during heteroepitaxial growth of diamond on Ir/YSZ/Si

AbstractIn situ boron doping of heteroepitaxial diamond films grown by microwave plasma chemical vapor deposition on Ir/YSZ/Si (001) is investigated. The study comprises the analysis of the gas phase by optical emission spectroscopy (OES) and measurements of B doped films by secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), and X‐ray diffraction (XRD). The OE intensity of BH species scales linearly with the concentration of the boron precursor trimethylboron (TMB) in the feed gas. Addition of CO2 as an oxygen source causes a proportional reduction of the BH signal. At a ratio C:O = 1, a reduction factor of ∼50 is obtained. It is shown for two diamond samples that the boron incorporation drops nearly identical to the BH emission intensity. We conclude that the influence of oxygen on boron incorporation is a pure gas phase effect. In contrast, CN and BH emission indicate a negligible interaction between N2 and TMB added to the feed gas. At the same time, preliminary growth rate measurements show that the boron background pressure in the chamber after growth with TMB completely cancels the growth acceleration by nitrogen up to N2 concentrations of 100 ppm which points to the dominance of surface processes. Heteroepitaxial diamond films grown on Ir at 50 mbar between 720 and 900 °C contain high intrinsic stress that varies from −2.2 GPa compressive at the lowest to slightly tensile at the highest deposition temperature. The observed behavior is similar to former work at 200 mbar in which effective climb of dislocations was suggested as responsible mechanism. Addition of boron rather enhances the stress formation than causing a relaxation. The B concentration in the heteroepitaxial films is deduced by SIMS, CL, and XRD and correlated with the TMB concentration in the gas phase.

Low-temperature preparation of flexible a-Si:H solar cells with hydrogenated nanocrystalline silicon p layer

In this paper we report on flexible a-Si:H solar cells prepared on polyethylene naphthalate (PEN) substrates using p-type hydrogenated nanocrystalline silicon thin films (p-nc-Si:H) as the window layer. The p-nc-Si:H films were prepared at low temperature (150 °C) using trimethylboron (TMB) as a dopant gas. The influence of the silane concentration (SC) on the electrical and structural properties of ultra-thin p-nc-Si:H as well as the performance of solar cells on PEN was investigated. The results show that the crystalline fraction and conductivity of p-nc-Si:H thin films diminished, while the deposition rate and RMS roughness of films increased, when the SC increases from 0.53% to 0.8%. For the a-Si:H solar cells on PEN with the non-textured electrodes, the best efficiency of 6.3% was achieved with the p-nc-Si:H thin films deposited at SC = 0.67%.

Study of large area hydrogenated microcrystalline silicon p-layers for back surface field in crystalline silicon solar cells

A series of hydrogenated microcrystalline silicon (μc-Si:H) p-layers for back surface field in crystalline silicon solar cells were deposited on glass substrates by the developed large area (45 cm×45 cm) plasma enhanced chemical vapour deposition processor operating at 13.56 MHz and various values of source gas trimethylboron (TMB) to H2 flowratio. The influence of deposition parameters on the large area p-layer performance was intensively studied, as well as the thin film uniformity, optical, electrical and structural performances by Raman, FTIR, Ellipsometry, etc. Arrhenius and Tauc plots were used to discuss the μc-Si:H thin film’s activation energy and the defects state distribution. When amorphous-microcrystalline transition state was obtained, the deposited p-doped μc-Si:H layers showed specific resistance of 38.3 Ω−1cm−1 at the flowratio of 0.66% and high crystallinity of 45%–50% with no further treatment. The effect of source gas flowratio, deposition rate, and source gas partial pressure on μc-Si:H thin film’s performance was also investigated.

Role of Trimethylboron to Silane Ratio on the Properties of <I>p</I>-Type Nanocrystalline Silicon Thin Film Deposited by Radio Frequency Plasma Enhanced Chemical Vapour Deposition

Trimethylboron (TMB) has been receiving attention as a valid alternative to diborane and methane mixtures for the deposition of p-type silicon films for applications in optoelectronic devices such as solar cells. In this paper we report on p-type hydrogenated nanocrystalline silicon carbide (nc-Si:C:H) films produced by standard 13.56 MHz plasma enhanced chemical vapour deposition technique, using TMB as gas source, under high hydrogen dilution (98%) and using high deposition pressures (3 Torr). The films obtained were characterized by spectroscopic ellipsometry (SE), Raman spectroscopy (RS), and electrical measurements to determine their optical, structural and electrical properties. We achieved conductivities as high as 8.3 (omega cm)(-1), one of the highest values of conductivity published to date using TMB with standard rf-PECVD. Spectroscopic ellipsometry modeling revealed that the films growth mechanism proceeds through a sub-surface layer mechanism that leads to the formation of nanocrystalline silicon.

ボロンドープしたＣＶＤダイヤモンド膜の機械的特性評価

For this study, single-crystal and polycrystalline diamond films with different boron contents were synthesized in a hot-filament chemical vapor deposition (CVD) apparatus to evaluate the mechanical properties of these films. Boron was added to the diamond by introducing B(CH3)3 :trimethyl boron diluted to 1000 ppm with hydrogen into the diamond-synthesis atmosphere. The synthesized diamond film's crystallinity was evaluated using Raman spectroscopy. The Hertz fracture strength was measured using a diamond-ball indenter. Furthermore, the wear resistance of the film was evaluated using a wear testing machine.The results indicate that the crystallinity of the single-crystal diamond film increased concomitantly with increasing boron content. Furthermore, the Hertz fracture strength increased by 20% with the addition of boron. Results clarified that the wear volume of polycrystalline diamond film decreased to approximately one-third its usual value by the addition of boron. These results show that the mechanical properties of boron-doped diamond films can be improved considerably by adding an appropriate amount of boron.

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.

Metal-organic chemical vapour deposition of (BInGa)P: Density-functional calculations to the mechanisms

Using the density-functional method and clusters modelling steps of (BInGa)P(0 0 1) surfaces, chemisorption and desorption energies as well as related barriers are calculated for probable chemisorption structures formed by precursor molecules XZ 3 (X: B, Ga, In, P; Z: H, Me=CH 3) during the metal-organic chemical vapour deposition (MOCVD). Reaction mechanisms, especially the stability of surface structures, the efficiency of the precursor molecules, and the rate-limiting steps, are obtained. In most cases, the final removal of hydrogen or methyl groups is the rate-limiting step. The deposition with hydrogen precursors (XH 3) is faster than the analogous deposition with methyl precursors (XMe 3). The deposition rate decreases from indium over gallium to boron. The rate of phosphorus deposition in surface dimers decreases from indium over gallium to boron dimers. Trimethylphosphine (TMP) is a less suitable precursor. Boron antisite deposition and formation of BGa and BIn alloys is less probable. The formation of an elementary boron phase by BH 3 is less probable and can be fully prevented by using trimethylboron (TMB) precursors. The differences in the reaction behaviour in comparison with (BInGa)As, investigated previously, are discussed.

Highly conductive p-type nanocrystalline silicon films deposited by RF-PECVD using silane and trimethylboron mixtures at high pressure

In this paper we present a study of boron-doped nc-Si:H films prepared by PECVD at high deposition pressure (≥4 mbar), high plasma power and low substrate temperature (≤200 °C) using trimethylboron (TMB) as a dopant gas. The influence of deposition parameters on electrical, structural and optical properties is investigated. We determine the deposition conditions that lead to the formation of p-type nanocrystalline silicon thin films with very high crystallinity, high value of dark conductivity (>7 (Ω cm) −1) and high optical band gap (≥1.7 eV). Modeling of ellipsometry spectra reveals that the film growth mechanism should proceed through a sub-surface layer mechanism that leads to silicon crystallization. The obtained films are very good candidates for application in amorphous and nanocrystalline silicon solar cells as a p-type window layer.

Boron Doping in Hot Filament MCD and NCD Diamond Films

AbstractConductive diamond films are essential for electronic applications of diamond but there is still a poor understanding of the effects that growth conditions, grain size and film thickness have on the ultimate conductivity of the film. One of the unique advantages of hot filament diamond is the ability to grow both MCD and NCD films to moderate thicknesses over large areas with little or no change in morphological characteristics such as grain size. In addition the grain size of the film can be altered without the necessity of adding additional gases to the process or unduly increasing the carbon to hydrogen ratio. This gives us an opportunity to investigate electrical conductivity as a function of grain size and thickness within a simple methane, hydrogen, and boron chemical environment over areas which are large enough to support significant production levels of MEMS and other diamond based electronics. In this study the boron source was selected to be trimethyl boron gas to avoid any source of oxygen which could alter the growth conditions and to guarantee that any byproducts of the dopant would be primarily methyl based. The films were grown to various thicknesses up to 5 micrometers and grain sizes from NCD to full MCD at all thicknesses. This paper explores the effects of both grain size and film thickness on the electrical conductivity of the film as well as the absolute doping levels within the film.

Electrical properties/Doping efficiency of doped microcrystalline silicon layers prepared by hot-wire chemical vapor deposition

Microcrystalline silicon (μc-Si) doped films were prepared by hot-wire chemical vapor deposition (HWCVD) to investigate the doping efficiency. The incorporation probability of different dopant atoms into the solid-phase is always increasing with the doping gas concentrations, but very different for the doping gases used: trimethylboron (TMB), boron trifluoride (BF 3) and phosphine (PH 3). At the same doping gas concentration in the process gas the incorporation of phosphorus atoms into the solid μc-Si phase is much larger than that of boron atoms with respect to the dissociation probability of the doping gases. The electron and hole concentrations, estimated from Hall measurements, are directly related to the solid phase concentration of the doping atoms and independent of the type of dopant and the doping gas used. This results in an equal doping efficiency of about 20 % for the incorporated B and P atoms in doped HWCVD μc-Si films. For the dopant atom concentration regime investigated the doping efficiency of B atoms is in good agreement with corresponding PECVD doping efficiencies however, the doping efficiency of P atoms is considerably lower for our n-doped films.

P-doped μc-Si:H window layers prepared by hot-wire CVD for amorphous solar cell application

We report on boron-doped μc-Si:H films prepared by hot-wire chemical vapor deposition (HWCVD) using silane as a source gas and trimethylboron (TMB) as a dopant gas and their incorporation into all-HW amorphous silicon solar cells. The dark conductivity of these films was in the range of 1–10 (Ω cm) −1 . The open circuit voltage V oc of the solar cells was found to decrease from 840 mV at low hydrogen dilution H-dil=91% to 770 mV at high H-dil =97% during p-layer deposition which can be attributed to the increased crystallinity at higher H-dil and to subsequent band edge discontinuity between μc-Si:H p- and amorphous i-layer. The short circuit current density J sc and the fill factor FF show an optimum at an intermediate H-dil and decrease for the highest H-dil. To improve the conversion efficiency and the reproducibility of the solar cells, an amorphous-like seed layer was incorporated between TCO and the bulk p-layer. The results obtained until now for amorphous solar cells with and without the seed layer are presented. The I–V parameters for the best p–i–n solar cell obtained so far are J sc =13.95 mA/cm 2 , V oc =834 mV, FF=65% and η =7.6%, where the p-layers were prepared with 2% TMB. High open circuit voltages up to 847 mV could be achieved at higher TMB concentrations.

Carbon nanostructure field emission devices

The microwave plasma chemical vapor deposition (MPCVD) method is capable of synthesizing various forms of carbon allotropes such as diamond, carbon nanotubes (CNTs), and diamondlike carbon (DLC) while varying the growth parameters or utilizing substrate coated with catalytic thin film. In this article, needlelike carbon nanostructures (CNs) were synthesized utilizing high power (5kW) and high working pressure (120Torr) MPCVD on a thin catalytic film of nickel with a diffusion barrier layer of titanium on a micropatterned silicon substrate. The effects of in situ doping by trimethylboron (TMB) on the morphologies and field emission properties of the CNs were also investigated. Straight, needlelike CNs with random orientation were obtained for 15min growth time with or without TMB doping. However, the CNs appear to transform into diamondlike nanocrystals after prolonged growth of 30min with TMB doping. Unlike MPCVD grown CNTs, it was found that the CNs have strong adhesion to the substrate and could withstand postgrowth processing such as ultrasonic agitation cleaning in solvents. Field emission tests performed show that in situ TMB doping of the patterned needlelike CNs lowers the turn-on field of the cathode. A vacuum field emission triode with self-aligned gate utilizing CNs as the field emitter is also fabricated.

Engineering Design, Installation, and Conditioning of Ferritic Steel Plates/Wall for AMTEX in JFT-2M

The JFT-2M tokamak has been modified three times during the Advanced Material Tokamak EXperiment (AMTEX) program to investigate the compatibility of the low-activation ferritic steel F82H with tokamak plasmas as structural material for future reactors. The ferritic steel plates/wall were installed inside and/or outside of the vacuum vessel to reduce the ripple of the toroidal magnetic field step by step through three modifications. This paper focuses on engineering aspects of these modifications: electromagnetic analysis to find a suitable way to attach these plates, installation procedure to keep small tolerances, and a three-dimensional magnetic field measurement device used to obtain information of the actual shape of the vacuum vessel used as a standard installation surface. To maintain good surface conditions of the ferritic steel plates/wall that rust easily, careful treatment was executed before the installation. To reduce oxygen impurities further, a boronization system with trimethyl boron, which is safe and easy to operate, was developed.

Electrochemical sensing using nanodiamond microprobe

Boron doped nanodiamond microprobe has been fabricated and characterized. Nanodiamond was deposited on sharpened tungsten probes using PECVD, with TMB (Trimethyl boron) as the boron dopant source. The electrode characterization was performed in a single compartment three electrode cell to detect Fe(CN) 6 4− with KCl as background. Nanodiamond microprobe demonstrates reversible kinetics during electrochemical analysis with low faradaic current and high signal to background ratio. The nanodiamond film shows structural stability for prolonged analysis without the need of surface pretreatment. There is no indication of adsorption of analytes at the nanodiamond surface. The characterization when performed for different active areas of the electrode, a stable increase in oxidation current was obtained with increase in scan rate. The excellent oxidation and reduction current responses make it an excellent sensor for electrochemical analysis and detection.

Microcrystalline B-doped window layers prepared near amorphous to microcrystalline transition by HWCVD and its application in amorphous silicon solar cells

The electronic and structural properties of p-type microcrystalline silicon films prepared near the microcrystalline to amorphous (μc-amorphous) transition by hot-wire chemical vapor deposition are studied. Silane is used as a source gas while H 2 as diluent and trimethylboron (TMB) and boron trifluoride (BF 3) as doping gases. Increasing TMB concentration from 0.01% to 5% favors the amorphous growth whereas for BF 3 the crystalline fraction remains constant. The dark conductivity ( σ d) of μc-Si:H p-layers remains approximately constant for TMB = 1–5% at constant crystalline fraction X c. This dark conductivity behavior is attributed to the decrease in doping efficiency with increasing TMB concentration. The best initial efficiency obtained for a 400 nm amorphous pin solar cell with optimized μc-Si:H p-layer is 7.7% ( V oc = 874 mV, J sc = 12.91 mA/cm 2, FF = 68%).

Structural and electrical properties of trimethylboron-doped silicon nanowires

Trimethylboron (TMB) was investigated as a p-type dopant source for the vapor–liquid–solid growth of boron-doped silicon nanowires (SiNWs). The boron concentration in the nanowires was measured using secondary ion mass spectrometry and results were compared for boron-doping using TMB and diborane (B2H6) sources. Boron concentrations ranging from 1×1018 to 4×1019cm−3 were obtained by varying the inlet dopant∕SiH4 gas ratio. TEM characterization revealed that the B2H6-doped SiNWs consisted of a crystalline core with a thick amorphous Si coating, while the TMB-doped SiNWs were predominantly single crystal even at high boron concentrations. The difference in structural properties was attributed to the higher thermal stability and reduced reactivity of TMB compared to B2H6. Four-point resistivity and gate-dependent conductance measurements were used to confirm p-type conductivity in the TMB-doped nanowires and to investigate the effect of dopant concentration on nanowire resistivity.

Fabrication and Electrical Characterization of Silicon Nanowire Arrays

ABSTRACTHigh density boron-doped silicon nanowire arrays were fabricated within the pores of anodized alumina membranes via vapor-liquid-solid (VLS) growth Anodized alumina membranes with a nominal pore diameter of 200 nm served as templates for the sequential electrodeposition of silver, cobalt, and gold which served as the backside electrical contact, ohmic contact metal and catalyst metal for VLS growth, respectively. Boron-doped silicon nanowires were then synthesized within the pores by VLS growth using silane (SiH4) and trimethylboron (TMB) gas sources. Arrays of Al dots were deposited on the top surface of the membrane after nanowire growth. A series of samples was prepared with different SiNW lengths and boron doping levels. Two point probe measurements were used to measure the I-V characteristics of the silicon nanowire arrays before and after annealing. Nanowire resistivity and contact resistance were determined from plots of resistance versus nanowire length. The resistivity of the SiNW was observed to decrease with the addition of TMB during growth.

322 プラズマ CVD 法によるアモルファス炭素膜の合成と電気的特性の評価

In this study, we investigated electrical properties of amorphous carbon (a-C : H) films fabricated by plasma CVD. First, photovoltaic cells consisting of Au/ a-C : H films / n-Si (p-Si) /In-Ga films were fabricated with changing deposition condition. Deposition of a-C"H films were performed using methane as a source gas. Nitrogen and tri-methyl boron (TMB) were also used as the doping gases. Under the light illumination (Xe are lamp at 100mW/cm^2), this cell shows photovoltaic behavior with short circuit current of 0.3mA/cm^2,open circuit voltage of 0.3V and energy conversion efficiency of 0.023%. Secondly, we investigated field emission from a-C : H on ITO films. The film shows field emission at the surface potential barrier of 4∿4.5eV.

OPTICAL PROPERTIES OF TRIMETHYLBORON AND NITROGEN CODOPED AMORPHOUS CARBON FILMS

We report on the efficient photoluminescence (PL) and optical properties of hydrogenated amorphous carbon thin films codoped with nitrogen and trimethylboron (TMB) grown by rf plasma-enhanced chemical vapor deposition at room temperature. The study clearly shows the observation of discrete PL emission peaks. The PL intensity of the film deposited with 20 sccm TMB is more than 103 times than that of the film deposited without TMB. The change of optical bandgap and PL emission energy with TMB flow rate are discussed based on sp3 and sp2 C networks. Angular dependence of the PL spectra revealed that the origin of multiple sharp peaks is due to Fabry-Perot cavity interference effect.

Effect of boronization on ohmic plasmas in NSTX

Boronization of NSTX has allowed access to higher density higher confinement plasmas. A glow discharge with 4 mtorr helium and 10% deuterated trimethyl boron deposited 1.7 g of boron on the plasma facing surfaces. Ion beam analysis of witness coupons showed a B + C areal density of 1018 cm-2 corresponding to a film thickness of 100 nm. Subsequent ohmic discharges showed oxygen emission lines reduced by a factor of 15, carbon emission reduced by a factor of two and copper reduced to undetectable levels. After boronization, the plasma current flat-top time increased by 70% enabling access to higher density higher confinement plasmas.