Boron-doped Films Research Articles

Absence of boron aggregates in superconducting silicon confirmed by atom probe tomography

Superconducting boron-doped silicon films prepared by gas immersion laser doping (GILD) technique are analyzed by atom probe tomography. The resulting three-dimensional chemical composition reveals that boron atoms are incorporated into crystalline silicon in the atomic percent concentration range, well above their solubility limit, without creating clusters or precipitates at the atomic scale. The boron spatial distribution is found to be compatible with local density of states measurements performed by scanning tunneling spectroscopy. These results combined with the observations of very low impurity level and of a sharp two-dimensional interface between doped and undoped regions show that the Si:B material obtained by GILD is a well-defined random substitutional alloy endowed with promising superconducting properties.

Comparison study of structural and optical properties of boron-doped and undoped graphene oxide films

We prepared boron (B)-doped graphene oxides (GOs) by means of annealing the films, which were obtained from the suspensions of GO and H3BO3 in N,N-Dimethylformamide solvent. The interplanar spacing of as-synthesized GO in X-ray diffraction spectra has been reduced by the thermal annealing at 1100°C. First-order Raman spectra revealed that the intensity ratio of the D and G bands of B-doped GO was significantly lower than those of as-synthesized and annealed GOs, suggesting more graphitization of the B-doped GO due to doping effect. The C1s X-ray photoelectron spectroscopy (XPS) of B-doped GO films not only indicated that considerable amount of functional groups has been removed but also exhibited the peak of CB band at around 283.7eV. Additionally, the B1s XPS spectrum of B-doped GOs could be deconvoluted into several peaks centered at 187.2, 188.9, 190.3, 192.0 and 193.7eV, being attributed to the presence of B atom in B4C, B-sub-C, BC2O, BCO2 and B2O3, respectively. Comparison of the photoluminescence spectra of B-doped GO with that of 1100°C-annealed GO indicated that the overall intensity was decreased, presumably due to the B-induced graphitization. An additional band at around 600–700nm from B-doped GO is attributed to the generated boron carbide phases.

Development of Boron-Doped ZnO Films with Novel Thin Zn-Rich Film and Their Application to Solar Cells

In this paper, we report newly developed high-haze glass/zinc oxide (ZnO) substrates with low resistivity by a combination of unique etched soda-lime glass and bilayered ZnO films with a Zn-rich (oxygen-poor) layer. The high mobility and low resistivity of bilayered ZnO films could be obtained with Zn-rich conditions. By depositing the ZnO films onto textured glass substrates, the obtained films exhibit an excellent light-scattering property, while their electrical property is still good. Furthermore, the bilayered ZnO films with a Zn-rich layer did not negatively affect the transparency of the films. Employing the bilayered ZnO films with a Zn-rich layer and an rms roughness of about 274 nm as the front transparent conductive oxide (TCO) in hydrogenated amorphous silicon (a-Si:H) solar cells, we improved the performance and quantum efficiency (QE) of the fabricated solar cells, particularly in the short-wavelength region without the deterioration of open-circuit voltage or fill factor. Thus, the developed glass/bilayered ZnO film with a Zn-rich layer is a new promising material since its resistivity is low while its light-scattering property is still high.

Development of Boron-Doped ZnO Films with Novel Thin Zn-Rich Film and Their Application to Solar Cells

In this paper, we report newly developed high-haze glass/zinc oxide (ZnO) substrates with low resistivity by a combination of unique etched soda-lime glass and bilayered ZnO films with a Zn-rich (oxygen-poor) layer. The high mobility and low resistivity of bilayered ZnO films could be obtained with Zn-rich conditions. By depositing the ZnO films onto textured glass substrates, the obtained films exhibit an excellent light-scattering property, while their electrical property is still good. Furthermore, the bilayered ZnO films with a Zn-rich layer did not negatively affect the transparency of the films. Employing the bilayered ZnO films with a Zn-rich layer and an rms roughness of about 274 nm as the front transparent conductive oxide (TCO) in hydrogenated amorphous silicon (a-Si:H) solar cells, we improved the performance and quantum efficiency (QE) of the fabricated solar cells, particularly in the short-wavelength region without the deterioration of open-circuit voltage or fill factor. Thus, the developed glass/bilayered ZnO film with a Zn-rich layer is a new promising material since its resistivity is low while its light-scattering property is still high.

Roughness-based monitoring of transparency and conductivity in boron-doped ZnO thin films prepared by spray pyrolysis

Sprayed polycrystalline ZnO and boron-doped ZnO thin films composed of spherical grains of 25–32nm in diameters are used in roughness measurement and further correlated with the transparency and the conductivity characteristics. The surface roughness is increased up to Zn0.98B0.02O and then declined at higher boron concentrations. The sprayed ZnO films revealed ≥95% transmittance in the visible wavelength range, 1.956×10−4Ωcm electrical resistivity, 46cm2/Vs Hall mobility and 9.21×1021cm−3 charge carrier concentration. The X-ray photoelectron spectroscopy study has confirmed 0.15eV binding energy change for Zn 2p3/2 when 2at% boron content is mixed without altering electro-optical properties substantially. Finally, using soft modeling importance of these textured ZnO over non-textured films for enhancing the solar cells performance is explored.

Controlling spatial distribution of thermal poling induced second-order optical nonlinearity with multilayered structures

Fused silica plates with boron-doped silicate multilayered thin films are thermally poled to create second-order optical nonlinearity for nonlinear optical applications. Measurement results from second harmonic microscopy show that the spatial distribution of the induced nonlinearity peaks at the interfaces between different layers where there is an abrupt change in boron concentration. A simple model is suggested to simulate the nonlinearity-trapping effect at the interfaces. This nonlinearity-trapping effect is not restricted to interfaces with abrupt refractive index changes; results from silica plates with deposited multilayered pure silica thin films show that the interface between the silica substrate and the silica thin film also has the nonlinearity-trapping effect.

Conductivity enhancement by fluorine doping in boron-doped ZnO thin films deposited by the electrospraying method

ZnO thin films co-doped with boron and fluorine (B, F–ZnO) were deposited by the electrospraying method onto a heated glass substrate. The characteristics of the films were investigated as a function of dopant concentrations in the solution. X-ray diffraction studies revealed that all the prepared films were polycrystalline in nature and exhibited the ZnO hexagonal wurtzite structure with preferential orientation along the (002) crystal plane. In addition, shift in the XRD patterns was observed and the crystal orientation was changed at a certain amount of fluorine (>6at%) in the starting solution. Analyses of X-ray diffraction and X-ray energy dispersive patterns demonstrate that fluorine and boron have been successfully doped into the ZnO thin films. Like these studies, the scanning electron micrographs showed that the grain size tends to decrease by the addition of fluorine. It was also observed that 2at% boron and 6at% fluorine was the optimal amount in order to achieve the minimum resistivity and maximum transmittance. The minimum value of resistivity of about 1.01×10−4Ωcm and high optical transmittance of 98% in the visible region were obtained for 2at% boron and 6at% fluorine co-doped ZnO films. Moreover, the present values of resistivities are closest to the lowest resistivity values among the doped ZnO films and also closer to the indium tin oxide (ITO) resistivities that were previously reported. We confirmed that the boron and fluorine atoms substitution in the ZnO lattice imparts positive effects in terms of enhancing the free carrier concentration and density of films, which will further improve the electrical and optical properties. The films produced at optimum conditions are suitable for optical and electrical applications owing to their low resistivity and high optical transmittance in the visible range.

The combined effect of surface roughness and internal stresses on nanoindentation tests of polysilicon thin films

Flat, low-stress, boron-doped polysilicon thin films were prepared on crystalline silicon substrates by low pressure chemical vapor deposition. The films’ surface morphologies and internal stresses were investigated using scanning probe microscope and AFM-Raman, respectively. The elastic modulus (E) was measured along with the hardness (H) using the nanoindentation technique. It was found that films deposited at the highest temperature had the largest grain size and surface roughness. The internal stresses in the films are tensile stresses, which are not uniform over the surfaces and present the gradient distribution along the thickness. Both the surface roughness and the internal stresses affect the nanoindentation tests. The tensile stresses in the films give extra forces to the diamond indenter, so the depths of penetration should be larger than those obtained from the films with stress free for a given load, which leads to an underestimation of E as well as H. But under the applied conditions, the increasing surface roughness can not only lead to the reductions of depths of penetration but also cause the measurement values of E and H to be more dispersive and uncertain. So for a given load, if the maximum depth of penetration in the rough surface is smaller than that in the smooth surface, the surface roughness is the main factor affecting the nanoindentation tests. On the contrary, the tensile stress is the main factor.

Electrochemical preparation and characterization of a cobalt oxide–platinum composite with promising capacitive and electrocatalytic features

In the present work, boron-doped diamond polycrystalline films were used as support for direct anodic deposition of the cobalt oxide, and continuous Co3O4 coatings with reasonably good conductivity were obtained by appropriately adjusting the deposition charge. Further electrochemical deposition of platinum particles on the oxide substrate enabled the formation of a stable composite with a specific capacitance of ca. 431 F cm−3 that compares well with that available with similar materials obtained by non-electrochemical methods. Additional advantages of electrochemically obtained composites are the lower content of noble metal, the uniform distribution of the charge over an extended potential range, and, importantly, the simplicity of the preparation method. It was also found that when deposited on a Co3O4 substrate, Pt particles show, besides an enhanced active surface area, an improved catalytic activity for methanol anodic oxidation. This behavior was tentatively ascribed to the presence of a high amount of platinum-oxidized species.

Highly photosensitive properties of CdS thin films doped with boron in high doping levels

We report the photosensitive properties of CdS thin films doped with boron at high doping levels. Boron-doped CdS thin films were successfully prepared through the chemical bath deposition (CBD) method. The photosensitive properties of the boron-doped CdS thin films were significantly affected by the molar ratio of boric acid (H3BO3) to cadmium acetate (CdAc2) (0.001, 0.1, 0.15, and 0.25) and by NH3 concentration (7 and 14M). As the H3BO3/CdAc2 molar ratio increased, dark sheet resistance rapidly increased, and the boron-doped CdS thin film exhibited the highest room temperature photosensitivity (∼1×106 at 0.15–0.25 H3BO3/CdAc2 molar ratio). The photosensitive properties of the boron-doped CdS thin films were much higher than those previously reported in boron-doped CdS systems.

Dependence of ferromagnetic properties on growth oxygen partial pressure in boron-doped ZnO thin films

Boron-doped ZnO films were prepared by pulsed laser deposition technique. Magnetic, electrical, and optical properties of Zn1−x B x O films have been studied. It is found that the magnetic properties of the Zn1−x B x O films are sensitive to growth oxygen partial pressure. The films deposited under a high oxygen partial pressure of about 10 Pa appear to be ferromagnetic insulators at room temperature (RT). However, when the oxygen partial pressure decreases to 1.2 Pa, the films are non-ferromagnetic conductors at RT. Zn vacancies, which can be controlled by the oxygen partial pressure, are shown to be essential for realizing ferromagnetism (FM); on the other hand, the n-type nature of ZnO has no contribution to the FM observed in the B-doped ZnO films.

Synthesis of Boron-Doped C60 Film Using Plasma-Assisted Thermal Evaporation Technique and its Electrochemical Characterizations

Boron doped C60 (B:C60) thin films were synthesized by a plasma-assisted thermal evaporation system. Scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infra red (FTIR) and X-ray photo electron spectroscopy (XPS) were used to investigate the morphology and structural characteristics of the films, respectively. The electrochemical characterization of B:C60 films was then introduced as a coating layer for silicon film anodes in a lithium ion battery. Typical electrochemical measurements such as cyclic voltammetry (CV) and impedance spectroscopy were used to characterize the B:C60 coated silicon electrodes. CV profiles implied that B:C60 coating layer could act as a passive layer with respect to the insertion and extraction of lithium ions into the silicon film electrode. Moreover, impedance results showed that the coating layer contributed to the smaller charge transfer resistance at the electrode/electrolyte interface.

Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure

Metal-doped (B and Ta) ZnO thin films were deposited by the electrospraying method onto a heated glass substrate. The structural, electrical and optical properties of the films were investigated as a function of dopant concentration in the solution and also as a function of annealing temperature. The results show that all the prepared metal-doped ZnO films were polycrystalline in nature with a (0 0 2) preferred orientation. As the amounts of dopant were increased in the starting solution, the crystallinity and transmittance decreased. On the other hand, heat treatment of the films enhanced the transmittance, Hall mobility, carrier concentration and crystallinity. It was also observed that 2at.% is the optimal doping amount in order to achieve the minimum resistivity and maximum optical transmittance. As-deposited films have high resistivity and low optical transmittance. The annealing of the as-deposited thin films in air resulted in the reduction of resistivity. Depending on the characteristics of dopant, mainly ionic radius, the effects of dopant were studied on the properties of ZnO thin films. Boron and tantalum have been considered as dopants, tantalum being the superior of the two, since it showed the lower resistivity and higher carrier concentration as well as higher mobility. The minimum value of resistivity was 1.95×10−4Ωcm (15Ω/□) with an optical transmittance more than 93% in the visible region and minimum resistivity of 2.16×10−4Ωcm (18Ω/□) with an optical transmittance greater than 96% for 2at. % tantalum- and boron-doped ZnO films respectively. The present values of resistivities were closer to the indium tin oxide (ITO) resistivity and also closest to the lowest resistivity values among the ZnO films that were previously reported. The prepared films exhibit the good crystalline structure, homogenous surface, high optical transmittance and low resistivity that are preferable for optical devices.

Boron-Doped Nanocrystalline Silicon Thin Films Prepared by PECVD

Boron-doped nanocrystalline silicon thin films(p-nc-Si:H) were deposited on glass substrates by plasma enhanced chemical vapour deposition (PECVD) using SiH4/ H2/ B2H6. The effects of substrate temperature, rf power and diborane flow on the microstructure, the electrical properties of nanocrystalline silicon thin films have been investigated. The results show that, increasing substrate temperature, rf power and B2H6flow can improve the conductivity of P-Si thin film. However, exceeding one value, they are not advantageous to improve the conductivity due to the decrystallization of films. Hence, appropriate process conditions are crucial for the preparation of high quality p layer. crystalline volume fraction (Xc) 26.2 %, mean grain size (d) 3.5nm and conductivity 0.374S/cm, p-nc-Si:H thin film was deposited.

Fabrication of High-Quality Boron-Doped Microcrystalline Silicon Thin Films on Several Types of Substrates

Boron-doped (p-type) μc-Si:H thin film window layers are widely used in silicon thin film solar cell fabrication due to their low optical absorption and high doping efficiency compared with their amorphous counterparts. In this paper, the layer-by-layer method is investigated to fabricate high-quality thin p layers (< 30nm). To investigate the influence of the type of substrate, p layers are deposited onto planar glass and textured glass (bare or coated with ZnO:Al thin film). The crystalline volume fraction (crystallinity) and conductivity of the deposited p layers are measured to characterise the films’ properties. We find that by increasing the number of hydrogen plasma treatment steps and their duration, the films’ crystallinity and electrical properties improve strongly. We also find that the substrate surface roughness strongly influences the film properties. This may be due to the different nucleation conditions resulting from the various substrate topographies.

Window layer with p doped silicon oxide for high Voc thin-film silicon n-i-p solar cells

We investigate the influence of the oxygen content in boron-doped nanocrystalline silicon oxide films (p-nc-SiOx) and introduce this material as window layer in n-i-p solar cells. The dependence of both, optical and electrical properties on the oxygen content is consistent with a bi-phase model which describes the p-nc-SiOx material as a mixture of an oxygen-rich (O-rich) phase and a silicon-rich (Si-rich) phase. We observe that increasing the oxygen content enhances the optical gap E04 while deteriorating the activation energy and the planar conductivity. These trends are ascribed to a higher volume fraction of the O-rich phase. Incorporated into n-i-p a-Si:H cells, p-nc-SiOx layers with moderate oxygen content yield open circuit voltage (Voc) up to 945 mV, which corresponds to a relative gain of 11% compared to an oxygen-free p-layer. As a similar gain is obtained on planar and on textured substrates, we attribute the increase in Voc to the higher work function of the p-nc-SiOx layer made possible by its wider band gap. These results are attained without changing the dilution ratio of the 250 nm thick intrinsic layer. We also observe an enhancement of 0.6 mA cm−2 in short circuit current density in the short wavelengths due to the higher transparency of the p-nc-SiOx layer. Finally, an initial efficiency of 9.9% for a single junction 250 nm a-Si:H n-i-p solar cell on plastic foil is achieved with the optimization of the p layer thickness, the doping ratio of the front transparent conductive oxide, and the optical properties of the back reflector.

Structural, optical and electrical measurements on boron-doped CdO thin films

Several boron-doped CdO with different boron composition thin films have been prepared on glass substrate by a vacuum evaporation technique. The effects of boron doping on the structural, electrical and optical properties of the host CdO films were systematically studied. The X-ray diffraction study shows that some of B3+ ions occupied locations in interstitial positions and/or Cd2+-ion vacancies of CdO lattice. The band gap of B-doped CdO suffers narrowing by 30–38% compare to undoped CdO. Such band gap narrowing (BGN) was studied in the framework of the available models. Furthermore, a phenomenological evaluation of the dependence of band gap on the carrier concentration in the film samples is discussed. The electrical behaviours show that all the prepared B-doped CdO films are degenerate semiconductors. However, the boron doping influences all the optoelectrical properties of CdO. Their dc-conductivity, carrier concentration and mobility increase compare to undoped CdO film. The largest mobility of 45–47 cm2/V s was measured for 6–8% boron-doped CdO film. From near infrared transparent-conducting oxide (NIR-TCO) point of view, boron is effective for CdO donor doping.

Laser fired contacts applied to the rear surface of heterojunction silicon solar cells

In this work, we fabricate heterojunction silicon solar cells on p-type substrates whose rear surface configuration is based on dielectric passivation and laser fired contacts (LFC cells). This is an alternative to boron-doped amorphous silicon film, with which we also fabricate solar cells for direct comparison (HJ cells). As substrates, 3.5 and 0.8 Ω cm p-type double-side polished FZ c-Si wafers are used. Regarding surface passivation for highly doped substrates, LFC configuration has some advantage due to the higher difficulty in creating an efficient amorphous back surface field. Additionally, those substrates are also more advantageous in terms of carrier injection when the rear surface is locally contacted. Thus LFC cells made on 0.8 Ω cm substrates reach V oc values up to 680 mV, in the same range as that of their HJ cell counterpart, with better FF demonstrating that LFC configuration is a feasible alternative for highly doped substrates. Focusing on the impact of the distance between rear contacts on cell performance, we found a trade-off between open circuit voltage V oc and fill factor FF. Finally electroluminescence characterization and the dependence of V oc on pitch, modeled by Fischer's equation, indicate that the depassivated area due to the laser processing of the contacts is bigger than the contacted area.

Diffusion structural diagnostics of polycrystalline boron-doped diamond films

Emanation thermal analysis (ETA) has been used to characterize the thermal behavior of boron-doped diamond polycrystalline film samples prepared by microwave plasma-assisted chemical vapor deposition (MPCVD). The mobility of radon atoms in the diamond film samples was evaluated from the ETA results. From the diffusion structural diagnostics achieved by evaluating the ETA results it followed that the O-plasma treatment of the sample enhanced the mobility of radon atoms in the range of 50–200 °C, due to both structure disordering and removal of graphitic carbon. The structure disordering was suggested by the high-resolution XPS results. From the diffusion structural diagnostics data it followed that the annealing of the structure irregularities in the polycrystalline diamond films took place in the range of 250–450 °C, the annealing was more intense for the O-plasma-treated sample compared to the H-plasma-treated one, due mostly to the initially greater degree of structure irregularities.

A study on the electrical activation behavior of boron in Si thin film doped by IMD

The crystallization of amorphous silicon (a-Si) film and the electrical activation of dopants have been systematically studied. The crystallization of a-Si was realized by depositing an a-Si film of 800 Å thickness on a glass substrate using a Ni phase transformation catalyst, followed by annealing at 550 °C. Electrical activation and crystallization were accomplished at the same time and the effect has been compared with the normal process. Resistance changes with respect to the doses in three different crystalline structures, amorphous, poly and single crystalline silicon, have been compared to find the optimum saturation dose and annealing temperature. The grain boundary effect on the resistance at different doses was intensively studied in this work. The minimum resistance of 224 Ω/□ in a boron-doped poly-silicon thin film was obtained by annealing in a furnace at 550 °C, and 177 Ω/□ was obtained in boron-doped amorphous silicon thin film annealed by RTA for 1 min.