Improved Properties of a-SiC:H Alloys with Reduced Density of CH3 Radicals

1992 ◽  
Vol 258 ◽  
Author(s):  
S. S. Camargo ◽  
M. L. de Oliveira ◽  
A. A. Pasa ◽  
C. Gatts
Keyword(s):  
Refractive Index ◽  
Fermi Level ◽  
Carbon Content ◽  
Conduction Band ◽  
Conductivity Measurements ◽  
Hydrogen Atoms ◽  
Optical Gap ◽  
Hydrogen Dilution ◽  
Photo Conductivity ◽  
Reduced Density

ABSTRACTIn this paper we report on the properties of a-SiC:H alloys with reduced density of CH3 radicals obtained by hydrogen dilution of gases. A reduced density of voids, hydrogen content and density of carbon bonded hydrogen atoms, were obtained; while carbon content and density of Si-H bonds are not affected much. A reduction of the optical gap and an increase of the refractive index were observed and related to the reduced densities of CH3 groups and voids. Dark- and photo- conductivity measurements showed that a performance comparable to the best undiluted films may be easily achieved, associated with a shift of the dark Fermi level towards the conduction band.

Polymorphous Silicon Films Produced in Large Area Reactors by PECVD at 27.12 MHz and 13.56 MHz

2003 ◽  
Vol 762 ◽  
Author(s):  
H. Águas ◽  
L. Raniero ◽  
L. Pereira ◽  
E. Fortunato ◽  
P. Roca i Cabarrocas ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Spectroscopic Ellipsometry ◽  
Conductivity Measurements ◽  
Large Area ◽  
Structural Characterisation ◽  
Hydrogen Dilution ◽  
Infrared And Raman Spectroscopy ◽  
Impedance Probe ◽  
Si Films ◽  
Probe Measurements

AbstractThis work refers to a study performed on polymorphous silicon (pm-Si:H) at excitation frequencies of 13.56 and 27.12 MHz in a large area PECVD reactor. The plasma was characterised by impedance probe measurements, aiming to identify the plasma conditions that lead to produce pm-Si:H films. The films produced were characterised by spectroscopic ellipsometry, infrared and Raman spectroscopy and hydrogen exodiffusion experiments, which are techniques that permit the structural characterisation of the pm-Si films and to study the possible differences between the films deposited at 13.56 and 27.12 MHz. Conductivity measurements were also performed to determine the transport properties of the films produced. The set of data obtained show that the 27.12 MHz pm-Si:H can be grown at higher rates with less hydrogen dilution and power density, being the resulting films denser, chemically more stable and with improved performances than the pm-Si:H films grown at 13.56 MHz.

Structural Properties of a-Ge1-xCx:H Alloys Prepared by the RF Sputtering Technique

1997 ◽  
Vol 467 ◽  
Author(s):  
F. C. Marques ◽  
J. Vilcarromero ◽  
F. L. Freire
Keyword(s):  
Carbon Content ◽  
Rf Sputtering ◽  
Low Carbon ◽  
Infrared Transmission ◽  
Absorption Bands ◽  
Optical Gap ◽  
High Carbon Concentration ◽  
Bending Modes ◽  
Hydrogenated Amorphous ◽  
Hydrogenated Amorphous Germanium

ABSTRACTStructural and mechanical properties of hydrogenated amorphous germanium carbon (a-Ge1-xCx:H) alloys are presented. The films were prepared by the rf-co-sputtering technique using a graphite/germanium composed target. The carbon and germanium relative concentrations were determined by RBS, and the total hydrogen concentration by ERDA measurements. An increase in the optical gap was measured for low carbon content (0 < × < 0.15). For higher values of x the optical gap is almost constant. Infrared transmission absorption spectra show several absorption bands related to Ge-C stretching, C-Hn (n = 1,2,3) and Ge-H stretching and bending modes. The mechanical internal stress was strongly affected by the incorporation of carbon. The trends of the optical gap, refractive index, infrared absorption and mechanical stress as a function of the carbon content suggest that the high carbon concentration alloys have polymeric and/or graphite-like contribution in their structure.

An Ocean Refractometer: Resolving Millimeter-Scale Turbulent Density Fluctuations via the Refractive Index

2006 ◽  
Vol 23 (1) ◽  
pp. 121-137 ◽  
Author(s):  
Matthew H. Alford ◽  
David W. Gerdt ◽  
Charles M. Adkins
Keyword(s):  
Refractive Index ◽  
Density Fluctuations ◽  
Inertial Subrange ◽  
Conductivity Measurements ◽  
Velocity Fluctuations ◽  
Fiber Motion ◽  
Turbulent Spectrum ◽  
Ocean Measurements ◽  
Fiberoptic Sensor ◽  
Better Than

Abstract A fiberoptic sensor has been constructed to measure oceanic density fluctuations via their refractive index signature. The resolution (Δz = 1 mm, Δt = 0.2 ms) and precision (Δn &lt; 10−8, Δρ = 3.4 × 10−5 kg m−3) of the device are far better than other methods and are sufficient to resolve the entire turbulent spectrum. Spectra show the salinity Batchelor rolloff at levels undetectable via conductivity measurements. However, the low-wavenumber portion of the spectrum occupied by the turbulent inertial subrange (≈1 m–1 cm scales) is marred by noise resulting from fiber motion in response to turbulent velocity fluctuations. The technique is described, and the first ocean measurements are reported.

scholarly journals Moderate strain induced indirect bandgap and conduction electrons in MoS2 single layers

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
János Pető ◽  
Gergely Dobrik ◽  
Gergő Kukucska ◽  
Péter Vancsó ◽  
Antal A. Koós ◽  
...  
Keyword(s):  
Charge Carrier ◽  
Fermi Level ◽  
Conduction Band ◽  
Carrier Density ◽  
Tensile Strain ◽  
Charge Carrier Density ◽  
Conduction Electrons ◽  
Metallic Character ◽  
Optical Bandgaps ◽  
Biaxial Tensile Strain

Abstract MoS2 single layers are valued for their sizeable direct bandgap at the heart of the envisaged electronic and optoelectronic applications. Here we experimentally demonstrate that moderate strain values (~2%) can already trigger an indirect bandgap transition and induce a finite charge carrier density in 2D MoS2 layers. A conclusive proof of the direct-to-indirect bandgap transition is provided by directly comparing the electronic and optical bandgaps of strained MoS2 single layers obtained from tunneling spectroscopy and photoluminescence measurements of MoS2 nanobubbles. Upon 2% biaxial tensile strain, the electronic gap becomes significantly smaller (1.45 ± 0.15 eV) than the optical direct gap (1.73 ± 0.1 eV), clearly evidencing a strain-induced direct to indirect bandgap transition. Moreover, the Fermi level can shift inside the conduction band already in moderately strained (~2%) MoS2 single layers conferring them a metallic character.

Wide Bandgap Fluorinated Silicon-Carbide-Nitride Films Using NF3

1991 ◽  
Vol 219 ◽  
Author(s):  
H. C. Goh ◽  
S. M. Tan ◽  
H. A. Naseem ◽  
S. S. Ang ◽  
W. D. Brown
Keyword(s):  
Silicon Carbide ◽  
Refractive Index ◽  
Carbon Content ◽  
Power Density ◽  
Deposition Rate ◽  
Gas Flow ◽  
Substantial Reduction ◽  
Wide Bandgap ◽  
Amorphous Hydrogenated Silicon ◽  
Stainless Steel Reactor

ABSTRACTAmorphous hydrogenated silicon carbide has been studied extensively because of its properties as a wide bandgap material. However, a large amount of methane is needed to deposit the material. Also, the high carbon content of these films poses some problems. The addition of NF3 to the gas stream results in wide bandgap films with a substantial reduction in the required CH4 flow for deposition. Amorphous SiCx Ny :H:F films were prepared using rf glow discharge decomposition of silane, methane, and nitrogen trifluoride in a parallel-plate stainless steel reactor. Gas flow rate and power density were varied. For a gas mixture containing 6% NF3 and 78% CH4, FTIR measurements reveal a reduction in C-H peak heights at 2960 cm-1 and 2880 cm-1 with respect to the Si-H peak at 2080 cm-1 indicating a smaller carbon content in the film. The C-H peaks shift to higher wavenumbers with increasing NF3. The use of NF3 increases the bandgap from 2.6 to 3.14 eV while reducing the refractive index from 2.12. to 1.87. A maximum deposition rate of 625 A/min was achieved. This should be compared to the very low deposition rate of 18 A/min for comparable bandgap Si-C films deposited using 97% methane in silane. Increasing the deposition power density resulted in a larger bandgap and a smaller refractive index.

Increase in Schottky Barrier Height in the CoSi2/Si (100) Interface Caused by Hydrogen

1992 ◽  
Vol 281 ◽  
Author(s):  
A. D. Marwick ◽  
M. O. Aboelfotoh ◽  
R. Casparis
Keyword(s):  
Fermi Level ◽  
Schottky Barrier ◽  
Barrier Height ◽  
Schottky Barrier Height ◽  
Interface States ◽  
Hydrogen Atoms ◽  
Fermi Level Pinning ◽  
Gap States

ABSTRACTIt is shown that the presence of 8 × 1015 hydrogen atoms/cm2 in the CoSi2/Si (100) interface causes an increase in the Schottky barrier height of 120 meV, and that passivation of dopants in the substrate is not the cause of this change. The data is evidence that the position of the Fermi level in this interface is controlled by defect-related interface states. After hydrogenation the Schottky barrier height agrees with that predicted by theory for Fermi level pinning by virtual gap states of the silicon.

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