Doped Amorphous Research Articles

Peculiar Magnetic Features and Superconductivity in Sulfur Doped Amorphous Carbon

We report on magnetic studies of inhomogeneous commercial and synthesized amorphous carbon (a-C) and a-C doped with sulfur (a-CS) powders which exhibit (i) peculiar magnetic behavior and (ii) traces of two superconducting (SC) phases TC ~ 33 and at 65 K. (i) The temperature dependence of zero-field-cooled (ZFC) curves measured up to room temperature show well distinguished elusive peaks at around 50–80 K, and their origin is not yet known. These peaks are totally washed-out in the second ZFC sweeps and in the FC branches as well. As a result, in the vicinity of the peaks, the FC curves lie below the ZFC peaks (FC < ZFC), a phenomenon which is rarely observed. These magnetic anomalies are intrinsic properties of a-C and a-CS materials (ii) SC was observed in three different a-C sources: (a) The commercial a-C powder contains 0.21% of sulfur and it is suggested that two different a-CS phases (at 33 and 65 K) are the origin of the two SC states observed. The compositions of these two phases are not yet unknown. The small SC volume fractions of the 33 K phase can be enhanced by a solid reaction with additional sulfur at 250 °C; (b) the synthesized (a-C) powder (obtained from decomposition of sucrose) is not SC. However, when mixed with sulfur and heated at 400 °C under a protective atmosphere, the a-CS powder obtained also show traces of a SC phase at TC = 42 K; (c) The same occurs in a-C thin films. The as-grown films are not SC but a SC phase at TC = 34 K emerges after the films were reacted with sulfur at elevated temperatures. It is concluded, therefore, that all SC phases observed are due to different unknown a-CS phases. Since the a-C and a-CS powders possess SC and magnetic states, we believe that these powders resemble the high TC curates and Fe-As based systems in which the SC and the magnetic states are closely related to each other.

UV Laser Annealing Effect on Mechanical Properties of Boron Doped Amorphous Carbon Films As Hardmasks

The hard forms of amorphous carbon (a-C, diamond like carbon) include hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon have raised interest as coating materials. Recently, boron doped amorphous carbon films have been studied as hardmask materials. The hardmasks are utilized to fabricate advanced semiconductor devices, including dynamic random access memory (DRAM) and vertical NAND flash memory. As decreasing of feature sizes on DRAM and NAND, the hardmask materials need to exhibit a high etch selectivity with low internal stress and good mechanical strength. In this work, we have prepared boron doped amorphous carbon film deposited with the fixed B2H6 flow rate as a function of the process temperature using plasma enhanced chemical vapor deposition (PECVD). Boron has been widely known efficient dopant for passivating the oxidation of various carbon materials. We investigated the physical and optical properties of film with the refractive index, hardness and chemical bonding configuration. Especially, the effect of ultraviolet (UV) laser annealing on the hardness was studied using nano-indentation. UV annealing caused a change of chemical bonding configuration, i.e., sp2/sp3 bonding ratio and C-H bonds, through analysis of the Fourier transform-infrared (FT-IR) and RAMAN spectrum. UV annealed boron doped amorphous carbon thin films exhibited an enhanced hardness, which leads to high etch selectivity. Our results could provide a route to high etch selective hardmask materials development.

WEAR OF Si OR B DOPED AMORPHOUS CARBON COATINGS

The paper describes a complex wear research on DLC (amorphous carbon) doped with boron (B) and silicone (Si). The tests were carried out in two different sliding systems: flat–on–flat (ring contact, unidirectional sliding) and ball–on–flat (reciprocating sliding). Water and medical saline solutions were used as lubricants. A comparative analysis of the results revealed differences in the initiation and progress of wear and the endurance with regard to coating’s composition, lubricant and contact geometry. The results obtained from the tests show the influence of the additive element on the wear resistance and the high dependency of coatings’ performance in the type of contact and of the lubricant used. In all cases analysed, the use of medical saline solution resulted in accelerated wear or an increased result scatter in comparison to pure water lubrication.

Properties of Boron Doped Amorphous Carbon Films at -30 V and -50 V for Carbon Based Solar Cell Applications

The a-C:B film were prepared by mixing vapor of hydrocarbon palm oil, boron dopant, carrier gas, and argon in the chamber deposited at -30 V and -50 V of negative bias voltage. The effect of these negative bias voltage on the thickness, electrical and electronic properties of a-C:B film were investigated. It was observed, the optical band gap slightly changed (2.0 eV to 2.04 eV). The fabricated solar cell with the configuration of Au/p-C:B/n-Si/Au achieved conversion efficiency (η) of 0.192% at applied bias voltage of -50 V. This result showed by the applied of negative bias voltage can controlled the interstitial doping of boron in the amorphous carbon films network.

Synthesis of Antimony Doped Amorphous Carbon Films

We report the effects of antimony (Sb) doping on the electrical and optical properties of amorphous carbon (a-C:H) films grown on silicon and copper substrates by magnetron sputtering deposition. For film deposition, the mixture targets fabricated from carbon and antimony powders was used. The atomic concentration of carbon, hydrogen, and antimony, in the film deposited from the 1.0 mol% Sb containing target were 81, 17, 2 at.%, respectively. These elements were homogeneously distributed in the film. On the structural effect, the average continuous sp2 carbon bonding networks decreased with Sb concentration increasing, and defects in the films were increased with the Sb incorporation because atomic radius of Sb atoms is twice larger size than that of carbon. The optical gap and the electrical resistivity were carried out before and after the Sb doping. The results show that optical gap dropped from 3.15 to 3.04 eV corresponding to non-doping to Sb-doping conditions, respectively. The electrical resistivity reduced from 10.5 to 1.0 MΩm by the Sb doping. These results suggest the doping level was newly formed in the forbidden band.

Properties of Iodine Doped Amorphous Carbon Thin Films Grown by Thermal CVD

Thin film of undoped and doped amorphous carbon has been achieved using the simple thermal CVD system in an ambient gas of Ar and Ar with I2, respectively. The electrical and optical properties of the iodine doped amorphous carbon (a-C:I) thin films were studied. The incorporation of iodine into the amorphous carbon thin film results in increase of electrical conductivity as doping temperature increase up to 400°C, which indicates that doping effect of iodine. Heterojuction is confirmed by rectifying current-voltage characteristics of a-C:I/n-Si junction. The decreasing of optical band gap from 0.54 to 0.25 eV after iodine doping was determined which contribute to induce graphitization in the films. Raman result indicates that sp2 and sp3 bonded carbon atoms were dominated in the both with and without iodine doped thin films.

Characterization of Boron Doped Amorphous Silicon Films by Multiple Internal Reflection Infrared Spectroscopy

ABSTRACTIn this study, we employed Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) to characterize chemical bonding structures of boron doped hydrogenated amorphous silicon (a-Si:H(B)). This technique has been shown to provide over a hundred fold increase of detection sensitivity when compared with conventional FTIR. Our MIR-IR analyses reveal an interesting counter-balance relationship between boron-doping and hydrogen-dilution growth parameters in PECVD-grown a-Si:H. Specifically, an increase in the hydrogen dilution ratio (H2/SiH4) was found to cause the increase in the Si-H bonding and a decrease in the B-H and SiH2 bonding, as evidenced by the changes in corresponding IR absorption peaks. In addition, although a higher boron dopant gas concentration was seen to increase the BH and SiH2 bonding, it also resulted in the decrease of the most stable SiH bonding configuration. The new chemical bonding information of a-Si:H thin film was correlated with the various boron doping mechanisms proposed by theoretical calculations.

Channel Switching Effect and Magnetoresistance in Iron Doped Amorphous Carbon Films on Silicon Substrates

Iron doped amorphous carbon films were deposited by pulse laser deposition on n-type silicon substrates. The as-fabricated structure shows a positive magnetoresistance (MR) of 34% at 5 T. Hall measurements show that the carbon film is hole-conducting and therefore a p-n heterojunction forms near the interface so that the current transport channel is transferred from the above carbon films at low temperatures to the Si substrates at high temperatures. The MR measured at high temperatures is attributed to the silicon substrates rather than to an inversion layer in the substrates as reported for many Metal/Insulating Barrier/Si structures.

Low Critical Concentration of Metal–Insulator Transition of Vanadium Doped Amorphous Boron

The metal–insulator transition (MIT) of V- and Zr-doped amorphous boron films (V x B 100- x , Zr x B 100- x ) was studied. The temperature dependences of the electrical conductivity, the X-ray diffraction patterns and the X-ray absorption fine structures were measured for the samples. The compositional boundary of the metal–insulator transition is found between x = 2.9 and 3.7 in V x B 100- x , and between x = 11 and 14 in Zr x B 100- x . It is considered that at the transition, the network of B 12 icosahedral clusters remains unchanged for V-doped films, while the network changes into an intermetallic compound-like structure for Zr-doped films. The low concentration of vanadium and no structural change for the transition of V-doped films are peculiar, while the critical concentration of Zr and the structural change of Zr-doped films are similar to those of transition-metal-doped amorphous silicon or germanium. The origin of the peculiarity of MIT for the V-doped films is discussed in relation to the metallic-covalent bonding conversion of the icosahedral clusters.

S043034 Sbドープアモルファス炭素膜の合成と電気的特性評価([S04303]環境調和型の表面改質および薄膜コーティング(3))

S043034 Sbドープアモルファス炭素膜の合成と電気的特性評価([S04303]環境調和型の表面改質および薄膜コーティング(3))

Using Boron Doped Amorphous Diamond Films as Window Layer of Amorphous Silicon Solar Cells

Boron doped amorphous diamond(a-D:B)films,which possess a wide optical gap and good p-type semi-conductive electroconductibility,were prepared using filtered cathodic vacuum arc system, whose target source was highly pure graphite incorporated with boron element.The intrinsic layer and the n-type layer of amorphous silicon solar ceils in a configuration of p-i-n were deposited using PECVD technology.The optical gap of the boron doped amorphous diamond films was characterized with a Lambda 950 UV-Vis photometer.The parameters of solar cells,such as open-circuit voltage,short- circuit current,fill factor and efficiency,were also measured.It shows that using the a-D:B films as the window layer of p-i-n structural amorphous silicon solar cell can increase the cell conversion efficiency by a roughly 10% relative improvement compared to the conventional amorphous silicon solar cell because of the enhancement of short wavelength response.

Cathodoluminescence of Fluorine and Nitrogen Doped Amorphous Carbon Films Deposited by a Filtered Cathodic Arc Plasma System

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Direct Determination of the Hole Density of States in Undoped and Doped Amorphous Organic Films with High Lateral Resolution

We investigate the density of states (DOS) for hole transport in undoped and doped amorphous organic films using high lateral resolution Kelvin probe force microscopy. Measurements are done on field effect transistors made of N,N1-diphenyl-N, N1-bis(1-naphthyl)-1,10-biphenyl-4,4II-diamine undoped or p doped with tetrafluoro-tetracyanoquinodimethane. We determine the DOS structure of the undoped material, including an anomalous peak related to interfaces between regions of different surface potential, the DOS doping-induced broadening, and doping-induced sharp peaks on the main DOS distribution.

Low Resistivity Boron Doped Amorphous Silicon-Germanium Alloy Films Obtained with a Low Frequency

AbstractThe structural and electrical properties of boron doped amorphous silicon-germanium alloy films, obtained using a low frequency plasma enhanced chemical vapor deposition (LF PECVD), are presented in this contribution. These thin films were deposited on a substrate heated at 270°C, and by decomposing a mixture of silane, germane, and diborane gases. The chemical bond structure was studied by Infrared Spectroscopy. Our results show that, for a constant diborane flow, the increase of germane flow enhances the incorporation of boron into the film; the peak at 2540 cm−1 becomes larger as the Ge content increases. Transport of carriers was studied by measuring current-voltage curves as a function of temperature. The conductivity increased from 10−6 to 10 (Ω-cm)−1, while the refraction index increased from 3.312 to 4.4458, for an increasing Ge content; this makes the films suitable for optical waveguide applications. On the other hand, the activation energy varied from 0.668 to 0.220 eV when the sample was doped with boron. The AFM images showed that the surface roughness was improved for an alloy with 50% of Ge.

Luminescent Holmium Doped Amorphous AlN Thin Films for use as Waveguides and Laser Cavities.

ABSTRACTHolmium doped AlN thin films have been deposited on flat silicon substrates and optical fibers of different diameters, in order to fabricate resonant cavities for lasers. In particular, the films on fiber substrates are expected to perform as cylindrical waveguides or “whispering gallery” mode cavities. The AlN films are deposited by reactive sputtering at liquid nitrogen temperature, using 100–200 Watts RF power, 5–8 mTorr nitrogen, using a metal target of Al and Ho. One micron thick films of AlN:Ho have been deposited on flat silicon substrates and 10 micron thick films on 80μm and smaller optical fibers. X-ray Diffraction and SEM studies show that films deposited on flat silicon are amorphous while those deposited on the fibers show columnar growth and some gain structure, most probably due to a temperature rise at the substrate during deposition. Cathodoluminescence (CL) emission is observed in thermally activated AlN:Ho in both crystalline and amorphous forms. An intense, narrow emission peak is observed at 549 nm. Less intense peaks are also observed at 362nm, 394 nm, 461 nm, and 659 nm. The most promising wavelength for our design is emission from the 5S2 → 5I8 transition at 549 nm.

Infrared Charge-Modulation Spectroscopy of Defects in Phosphorus Doped Amorphous Silicon

AbstractWe present infrared charge-modulation absorption spectra on phosphorus-doped amorphous silicon (a-Si:H:P) with doping levels between 0.17%-5%. At higher doping levels (1% - 5%) we find a sharp spectral line near 0.75 eV with a width of 0.1 eV. We attribute this line to the internal optical transitions of a complex incorporating four fold coordinated phosphorus and a dangling bond. This line is barely detectable in samples with lower doping levels (below 1%). In these samples a much broader line dominates the spectrum that we attribute to uncomplexed dopants. The relative strength of the two spectral features is in rough agreement with a model proposed by Street that has not been previously tested experimentally.

Optical Properties of Manganese Doped Amorphous and Crystalline Aluminum Nitride Films

An aluminum nitride (AlN) film deposited on silicon (100) was used as the substrate for growing manganese (Mn) doped AlN film by metal organic chemical vapor deposition (MOVCD). The (15.78 µm) under layer of AlN was grown at 615°C at a pressure of 10−4 Torr. The (2.1 µm) top layer of Mn-AlN was grown at the same temperature and pressure but doped with pulse valve introduction of the manganese decacarbonyl (100 ms on, 100 ms off). The film was then characterized ex situ with IR reflectance microscopy, X-ray diffraction, scanning electron microscopy imaging, cathodoluminescence, and X-ray fluorescence. The IR reflectance measurements showed a strong (A1) LO mode for AlN at 920 cm−1 and 900 cm−1 with a shoulder at 849 cm−1. X-ray Diffraction yielded three diffraction peaks at a 2θ position of 33, 36 and 38 degrees corresponding to 100, 002, and 101 lattice planes respectively. Cathodoluminescence results show strong visible emitted light from incorporated manganese. The relative percentage of manganese to aluminum was below the detection limit (0.01 %) of the X-ray fluorescence spectrometer. Amorphous Mn doped AlN films have also been grown using a low temperature atomically abrupt sputter epitaxial system. The amorphous Mn doped AlN showed no cathodoluminescence.

Optical Properties of Manganese Doped Amorphous and Crystalline Aluminum Nitride Films

AbstractAn aluminum nitride (AlN) film deposited on silicon (100) was used as the substrate for growing manganese (Mn) doped AlN film by metal organic chemical vapor deposition (MOVCD). The (15.78 [.proportional]m) under layer of AlN was grown at 615°C at a pressure of 10−4 Torr. The (2.1 [.proportional]m) top layer of Mn-AlN was grown at the same temperature and pressure but doped with pulse valve introduction of the manganese decacarbonyl (100 ms on, 100 ms off). The film was then characterized ex situ with IR reflectance microscopy, X-ray diffraction, scanning electron microscopy imaging, cathodoluminescence, and X-ray fluorescence. The IR reflectance measurements showed a strong (A1) LO mode for AlN at 920 cm−1 and 900 cm−1 with a shoulder at 849 cm−1. X-ray Diffraction yielded three diffraction peaks at a 2ø position of 33, 36 and 38 degrees corresponding to 100, 002, and 101 lattice planes respectively. Cathodoluminescence results show strong visible emitted light from incorporated manganese. The relative percentage of manganese to aluminum was below the detection limit (0.01 %) of the Xray fluorescence spectrometer. Amorphous Mn doped AlN films have also been grown using a low temperature atomically abrupt sputter epitaxial system. The amorphous Mn doped AlN showed no cathodoluminescence.

Photo and Thermal Stability of Chlorine Doped Amorphous Silicon TFTs

ABSTRACTThe Cl doped amorphous silicon film was deposited from SiH4, SiH2C12 and H2 gas mixture by PECVD process and their properties with various SiH2C12 flow rate is discussed. Controlling the amount of Cl doped was crucial for acquiring high stability TFT without lowering on current. Amorphous silicon and Cl doped amorphous silicon double layer TFT structure, with satisfactory on current and throughput, proved to be more stable than conventional amorphous silicon TFT in photo state and in elevated temperatures.

Laser Induced Melting and Crystallization of Boron Doped Amorphous Silicon

ABSTRACTTransient reflectivity experiments have been performed to measure the dynamics of laser-induced melting of amorphous silicon (a-Si) and the crystallization to μ-Si of films with different thicknesses on Corning 7059 glass. The laser-induced melting takes place with a velocity of 13 to 24 m/s, while the solidification is about a factor 10 slower. The crystallization starts at the Si/glass interface and at the surface. In the center of the films, Si remains liquid for an extended period of time. The crystallization dynamics point towards an heterogeneous morphology of laser-crystallized Si, where the surface and the interface layers are composed of small grains and the bulk of larger grains.