Boron-doped Films Research Articles

Diamond anvil cell with boron-doped diamond heater for high-pressure synthesis and in situ transport measurements

Temperature and pressure are essential parameters in the synthesis, evaluation, and application of functional materials. This study proposes the addition of a heating function to a high-pressure diamond anvil cell (DAC) with in situ measurement probes. The proposed DAC allows for simultaneous control of temperature and pressure within the sample space and can be used to synthesize functional materials under extreme conditions. The various components, namely, the heater, thermometer, and measurement probes, were fabricated with a boron-doped diamond epitaxial film and could be repeatedly used. The developed DAC was used to conduct the high-pressure annealing of a La(O,F)BiS2 single crystal and the high-pressure synthesis of EuFBiS2 superconductors. The proposed technique shows promise for further exploration of superconductors to broaden the research field.

Large microwave inductance of granular boron-doped diamond superconducting films

Boron-doped diamond granular thin films are known to exhibit superconductivity with an optimal critical temperature of Tc=7.2 K. Here, we report the measured in-plane complex surface impedance of boron-doped diamond films in the microwave frequency range using a resonant technique. Experimentally measured inductance values are in good agreement with estimates obtained from the normal state sheet resistance of the material. The magnetic penetration depth temperature dependence is consistent with that of a fully gapped s-wave superconductor. Boron-doped diamond films should find application where high kinetic inductance is needed, such as microwave kinetic inductance detectors and quantum impedance devices.

Maintaining superior crystallinity and conductivity in boron-doped nc-Si ultra-thin films by hydrogen plasma treatment

In view of using doped nanocrystalline Si (nc-Si) as the emitter layer in nc-Si/crystalline-Si heterojunction solar cells, a very thin (≤ 50 nm) emitter layer with high conductivity and superior crystallinity is optimum. In the present work, p-nc-Si:H thin film prepared in inductively coupled plasma chemical vapor deposition, without using additional H2-dilution in [SiH4 + B2H6 (1% in H2)]-plasma, retains conductivity ~10−1 S cm−1 and crystallinity ~68% at a low thickness (t) ~50 nm. The charge carrier transport through the heavily doped nc-Si network demonstrates reverse Meyer–Neldel characteristics for t ≥ 50 nm. However, with reduction to t < 50 nm, the evolution of the ultra-nanocrystalline dominated amorphous network, accompanied by accumulation of Si–H–Si platelet-like components in the grain boundary, leads to a drastic reduction in conductivity to 10−4 S cm−1. In this context, the post-deposition and short-time hydrogen plasma treatment (PSHPT) on the as-deposited ultra-thin (t ~30 nm) film becomes instrumental in substantially enhancing the crystallinity from 40% to 69% and increasing conductivity by two orders of magnitude to 10−2 S cm−1. The network modification by PSHPT proceeds via transformation of the surface and sub-surface weak bonds and is significant for the ultra-thin film compared to the thick film, due to retaining a superior surface-to-bulk ratio.

Investigation of structural, optical and radiation shielding properties of boron-doped In2O3 thin films

Investigation of structural, optical and radiation shielding properties of boron-doped In2O3 thin films

Effects of Surface Engineering of Copper Catalyst on the CVD Growth of Boron-Doped Graphene with a Solid Carbon and Boron Source

Chemical doping of boron atoms is essential to modify the electrical properties of graphene films. The synthesis of large-scale boron-doped graphene with high uniformity and good electrical properties is still a great challenge. To improve the quality and uniformity of boron-doped graphene, we introduced several methods to engineer the surface of the copper catalyst for chemical vapor deposition. The ethylic acid treatment proved to be more effective to remove surface impurities than the hydrochloric acid treatment. Moreover, electrochemical polishing showed the best performance in reducing the impurities and surface roughness in all the methods. The sheet resistance and carrier mobility of the boron-doped graphene film grown on the electropolished copper foil were 2.35 kΩ/□ and 1.15 × 103 cm2·V−1·s−1 at room temperature, respectively. Our results suggest that the boron-doped graphene grown on the electropolished copper catalyst possesses a high carrier mobility and less structural defects, which makes it suitable for application in optoelectronics.

Concurrent synthesis and boron-doping of amorphous carbon films by focused ion beam-assisted chemical vapor deposition

A method to directly deposit boron-doped amorphous carbon films via focused ion beam-assisted chemical vapor deposition is reported. The presence of boron in the deposited films was verified by X-ray photoelectron spectroscopy. Raman spectroscopy analysis confirmed the amorphousity of the films. The as-deposited films exhibited typical semiconducting behavior from electrical resistance versus temperature measurements. The presented fabrication technique is a one step process for the simultaneous deposition, boron-doping, and patterning of the films, and hence may offer an effective way to directly fabricate boron-doped amorphous carbon-based devices without the need for templates, which is highly advantageous for applications.

Substrate temperature dependence of material, optical, and electronic properties of boron-doped ZnO thin films

Abstract Sputtered boron-doped ZnO (BZO) thin films at deposition temperature ranging from 300 °C to 600 °C are studied in this work. The BZO films exhibit preferred orientation of (002) planes. The surface morphology is dependent on deposition temperature, characterized essentially by three distinct features. Hall-effect measurements suggest that the BZO film deposited at 400 °C show the optimum results of carrier concentration, mobility, and resistivity with values that can reach 2.06 × 10 20 cm−3, 5.38 cm2/ V ⋅ s , and 5.64 × 10 − 3 Ω ⋅ cm , respectively. By combining the optical band gap from transmittance spectra and work function from ultraviolet photoemission spectroscopy, the band structure of BZO films is derived. The positions of BZO energy levels presented in this study can provide insights into band engineering in BZO-based optoelectronic devices.

Spectroscopic ellipsometry investigation to study the microstructure evolution in boron-doped amorphous silicon films as a result of hydrogen dilution

Spectroscopic ellipsometry (SE) is a sophisticated technique to find the optical constants, bandgap and microstructure of thin layer. SE is used to study the microstructure evolution in boron-doped amorphous silicon films for different hydrogen flow rates (HFR). Spectral dependance of the real and imaginary parts of pseudo-dielectric constant is obtained at a fix angle of incidence (70°). Tauc–Lorentz (T–L) optical model is used to estimate the thickness, bandgap, optical constant and thickness of the top rough layer of the films, whereas Bruggeman effective medium approximation (BEMA) is applied to find the volume fractions of amorphous, crystalline and void phases. A shift in peak position from 3.65 to 4.1 eV in dielectric constant is observed as the hydrogen flow rate is increased from 30 to 70 SCCM. This is accompanied by the emergence of a peak near 3.4 eV, which belongs to the direct bandgap of c-Si. These observations suggest an improvement in microstructure of the films deposited at higher HFR. It is also supported by the observation that films deposited at higher HFR have higher magnitude of amplitude parameter and less broadening. Fitting of experimental data using BEMA also suggests that crystalline fraction increases and amorphous fraction decreases at higher HFR. The bandgap and thickness of top rough layer estimated from SE data are matched well with those obtained using transmission data and atomic force microscopy.

Low-temperature synthesis of conducting boron-doped nanocrystalline silicon oxide thin films as the window layer of solar cells

Low-temperature synthesis of highly transparent conducting B-doped (p-type) nc-SiOX:H films has been pursued by 13.56 MHz plasma-CVD, using a combination of SiH4, CO2 and B2H6, diluted by H2 and He. Higher substrate temperature (TS) encourages nanocrystallization in B-doped nc-SiOX:H network by reducing bonded H-content, while bonded O-content also reduces simultaneously. At optimized TS = 150 °C, p–nc-SiOX:H film having an optical band gap ~1.98 eV, high conductivity ~0.18 S cm−1, has been obtained via dopant-induced escalation of the electrically active carriers at a deposition rate ~5.3 nm/min. The p–nc-SiOX:H film appears as a promising window layer for the top sub-cell of multi-junction silicon solar cells. A single-junction nc-Si:H based p-i-n solar cell of efficiency (η) ~7.14% with a current-density (JSC) ~14.18 mA/cm2, reasonable fill-factor (FF) ~66.2% and open-circuit voltage (VOC) ~0.7606 V has been fabricated, using the optimum p-type nc-SiOX:H as the window layer deposited at TS = 150 °C.

Visible-Light-Responsive Antibacterial Property of Boron-Doped Titania Films

Pure titanium dioxide TiO2 photocatalytic substrates exhibit antibacterial activity only when they are irradiated with ultraviolet light, which comprises high-energy wavelengths that damage all life. Impurity doping of TiO2-related materials enables visible light to stimulate photocatalytic activity, which enhances opportunities for TiO2 to be used as a disinfectant in living environments. Boron-doped TiO2 displays visible-light-responsive bactericidal properties. However, because boron-derived compounds also exert notable antibacterial effects, most reports did not clearly demonstrate the extent to which the bactericidal property of boron-doped TiO2 is contributed by visible-light-stimulated photocatalysis. In addition, TiO2 thin films have considerable potential for applications in equipment that requires sterilization; however, the antibacterial properties of boron-doped TiO2 thin films have been examined by only a few studies. We found that boron-doped TiO2 thin films displayed visible-light-driven antibacterial properties. Moreover, because boron compounds may have intrinsic antibacterial properties, using control groups maintained in the dark, we clearly demonstrated that visible light stimulated the photocatalysis of boron-doped TiO2 thin films but not the residue boron compounds display antibacterial property. The bactericidal effects induced by visible light are equally potent for the elimination of the model organism Escherichia coli and human pathogens, such as Acinetobacter baumannii, Staphylococcus aureus, and Streptococcus pyogenes. The antibacterial applications of boron-doped TiO2 thin films are described, and relevant perspectives discussed.

Boron-doped graphene from boron-doped copper substrate for self-powered photodetector

We investigate a method to prepare boron-doped graphene (BG) using a boron-doped copper film as both the substrate for graphene growth and the boron dopant source. About 1.6 at.% of boron was incorporated in the BG film. The BG had a bilayer structure, whereas the undoped pristine graphene (PrG) had a monolayer structure. The graphene films were transferred to the surface of n-type Si to fabricate PrG/n-Si and BG/n-Si diodes. The BG/n-Si diode had a slightly larger Schottky barrier height than the PrG/n-Si, indicating p-type doping in the BG film. Both the BG/n-Si and PrG/n-Si exhibited self-powered photodetection to 0.3 mW/cm2 of 365 nm UV light, and the ON/OFF ratio was 1.5 × 104 for the BG/Si diode and 2.9 × 103 for the PrG/Si diode. Compared with the PrG/n-Si diode, the BG/n-Si had a higher ON/OFF ratio due to its lower dark current and a higher barrier height.

Enhancement of optical properties of boron-doped SiC thin film: a SiC QD effect

Silicon carbide quantum dots (SiC-QD) embedded inside the SiC thin film deposited on silicon (111) wafer is directly synthesized by modified chemical vapour deposition technique using boron-doped liquid polycarbosilane as a precursor. Subsequent microscopic characterization of the thin film exhibits the presence of QD, which is theoretically corroborated from the exciton Bohr radius. The film shows interesting visible and near-infra-red photoluminescence at room temperature with enhanced lifetime. In addition to the lifetime, the quantum efficiency in the visible emission was also enhanced substantially than what was reported previously.

Enhanced magnetic sensing performance of diamond MEMS magnetic sensor with boron-doped FeGa film

The coupling of single crystal diamond (SCD) micro-electromechanical systems (MEMS) through with a functional hetero-material provides the strategy to develop diamond MEMS sensors. Here a noncontact magnetic sensor based on SCD MEMS resonance system functionalized with a boron-doped FeGa (FeGaB) thin film owning excellent magneto-strictive properties on diamond is demonstrated to improve the magnetic sensitivity. The amorphous FeGaB thin film is beneficial for high magnetic sensing performance. The FeGaB/Ti/SCD MEMS magnetic sensor exhibits magnetic sensitivity of as high as 152.1 Hz/mT, which is over four times of those of FeGa/Ti/SCD MEMS magnetic sensors. The derivative of the Young’s modulus change with magnetic field (dE/dH) reaches a maximum value of 4.5 GPa/mT at 1.77 mT. By tailoring the magnetic properties with impurity dopant, one can markedly improve the sensitivity of the diamond MEMS magnetic sensitivity toward satisfying the figure-of-merits of ultra-high sensitivity, low noise level and high-reliability magnetic field operation.

Growth of low resistivity and high transparency boron-doped zinc oxide film by pulse laser deposition

0.5 wt% boron-doped zinc oxide (BZO) films were fabricated by utilizing pulse laser deposition under different growth temperature ranged from 250 to 450 °C. The effect of the growth temperature on the structural, optical, and electrical properties was investigated and discussed. The crystal structure and orientation of BZO thin films were examined by X-ray diffraction. All of the BZO films under various growth temperatures had strong c-axis (002)-preferred orientation. Optical transparency was high (>80%) over a wide spectral range from 400 nm to 700 nm, and the optical bandgap value of BZO are found to be in the range from 3.18 to 3.47eV. According to the experimental data, the resistivity of the BZO film was optimized at ~1.13 × 10−3 Ω-cm and significantly influenced by the growth temperature.

Improved Thermal Resistance and Electrical Conductivity of a Boron-Doped DLC Film Using RF-PECVD

Diamond-like carbon (DLC) film doped with boron has unique properties and displays higher thermal resistance, lower internal stress, and better electrical conductivity than un-doped DLC film; this makes it is suitable for various applications, especially in outer space. Radio-frequency plasma-enhanced chemical vacuum deposition of boron-doped DLC film was performed to determine the optimal percentage of boron for improving thermal resistance. Additional heat treatment and 40% B2H6/CH4 yielded the best electrical conductivity. X-ray photoelectron spectroscopy, thermal gravimetric analysis, Raman spectroscopy, and the four-point probe method were utilized to analyze the properties of boron-doped DLC film. The boron-doped DLC film displayed outstanding performance in terms of thermal resistance and electrical conductivity.

Atomic hydrogen passivation for photoresponsivity enhancement of boron-doped p-BaSi2 films and performance improvement of boron-doped p-BaSi2/n-Si heterojunction solar cells

Semiconducting barium disilicide (BaSi2) is an emerging material for solar cell applications, and therefore, defect passivation is critical for improving its solar cell performance. Herein, the effect of atomic hydrogen (H) on the photoresponsivity of 500 nm-thick boron (B)-doped p-BaSi2 films was examined. The photoresponsivity reached ∼4 A/W (about twice the highest reported value for H-passivated undoped BaSi2 films) in B-doped p-BaSi2 films exposed to an atomic H supply for 5 − 10 min because of an increased minority-carrier lifetime, as measured by the microwave-detected photoconductivity decay. Furthermore, a ≥15 min atomic H supply was found to degrade photoresponsivity. Ab initio studies were used to interpret and understand experimental observations by analyzing states in the gap region, which can act as traps, in B-doped p-BaSi2 with H incorporation. The effect that atomic H had on the performance of B-doped p-BaSi2/n-Si heterojunction solar cells was also studied. The saturation current density was found to decrease by three orders of magnitude with the atomic H supply, and the conversion efficiency was increased up to 6.2%. Deep-level transient spectroscopy revealed a reduction of defect densities induced by the atomic H supply. Both experimental and theoretical viewpoints show that an atomic H supply is beneficial for BaSi2 solar cells.

Transparent boron-doped zinc oxide films for antibacterial and magnetic applications

B-doped ZnO thin films have been synthesized by a sol–gel dip-coating deposition technique. Deposition conditions were optimized to achieve highly ordered thin films. XRD patterns confirm that B ions are inserted into the ZnO; lattice and the crystallite size decrease from 25.83 to 20.94 nm as the amount of B increases to optimal value (9 at.wt%). Synthesized B-doped ZnO thin films have ordered hexagonal wurtzite structures and granular morphology with high specific surface area. Optical transmittance spectra display transparency in the visible region. The band gap of the films decreases from 3.89 to 3.04 eV with the increase in B concentration. Band gap lowering is due to increase of defect level with the increase in B dopant percentage. The origin of the ferromagnetism is explained in terms of oxygen vacancies and Zn interstitials. Dielectric constant increases while DC conductivity and AC conductivity decrease with the increase in B doping. Antibacterial activity increases with the increase in B doping percentage but lower than undoped ZnO due to large crystallite size of B-doped ZnO nanostructures.

Investigation on the improved electrical and optical properties of trivalent boron-doped Cu2O thin film and fabrication of Cu2O:B/c-Si heterojunction diode

Boron-doped cuprous oxide (Cu2O:B) thin films were deposited on glass and silicon substrates via radio frequency (rf) magnetron co-sputtering at room temperature using metallic copper and boron targets. The influence of B doping on the morphology of Cu2O was studied using X-ray diffraction and spectrometric techniques. Optical transparency and bandgap of the doped films were improved compared to intrinsic Cu2O thin film. X-ray photoelectron spectroscopy confirms that Cu is in + 1 valance state even after doping. Electrical characteristics suggest enhanced p-type conductivity and reduction in resistivity with boron doping, due to the increase in charge carriers. Cu2O:B/c-Si heterojunction shows good rectifying (~ 104) behavior, and the small ∆Ev and high ∆Ec obtained from the flat band diagram suggests its potential application as hole-selective layer in c-Si solar cell.

Structural evolution of in situ boron-doped SiGe ultrathin film analyzed by multi-optical methods

In situ boron (B)-doped SiGe (BSG) layer is extensively used in the source (S)/(D) drain of metal-oxide-semiconductor field-effect transistors. An unexpected structural evolution occurs in BSG during metallization and activation annealing during actual fabrication, which involves a correlated interaction between B and SiGe. Herein, the complicated phenomena of the structural evolution of BSG were analyzed by 325 nm micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), reflective second harmonic generation (RSHG), and synchrotron x-ray diffraction (XRD). Optical inspection was integrated into these processes to establish a multi-optical method. 325 nm micro-Raman spectroscopy was used to determine variations in Si–Si, Si–Ge, and Ge–Ge bonds in BSG. XPS exhibited the binding energy evolution of Ge3d during different annealing processes at varied Ge ratios and B concentrations. RSHG revealed the polar Si-B and Ge-B bonds formed during annealing. Synchrotron XRD provided the structure and strain changes of BSG. Secondary-ion mass spectrometer profiles provided the species distribution, which was used to examine the results of multi-optical method. Furthermore, double-layered BSG (DBSG) with different B concentrations were analyzed using the multi-optical method. Results revealed that Ge aggregated in the homogeneous interface of DBSG, and that B dopants in BSG served as carrier providers that strongly influenced the BSG structure. However, BSG with excessive B concentration was unstable and increased the B content (SiB3) through metallization. For BSG with a suitable B concentration, the formation of Si–B and Ge–B bonds suppressed the diffusion of Ge from SiGe, thereby reducing the possibility of Ge loss and further B pipe-up in the heavily doped S/D region.

Deposition of boron-doped nanocrystalline silicon carbide thin films using H2-Ar mixed dilution for the application on thin film solar cells

Hydrogen-argon mixed dilution has been applied for the deposition of boron-doped nanocrystalline silicon carbide (nc-SiCx) thin films. The variations of structural, compositional, electrical and optical properties with the varying H2/Ar ratio are systemically investigated through various characterizations. It is shown that by using H2-Ar mixed dilution for deposition, B-doped nc-SiCx thin film possessing both wide optical band gap (∼2.22 eV) and high conductivity (∼1.9 S cm−1) can be obtained at the H2/Ar flow ratio of 360/140. In addition, the B-doped nc-SiCx thin films are fabricated as the window layers of a-Si thin film solar cells, and the highest conversion efficiency (8.13%) is obtained when applying the window layer with the largest optical band gap energy.