Morphology, Phonon Confinement and Properties of a-Si:H Films

2001 ◽  
Vol 664 ◽  
Author(s):  
Valeri Ligatchev
Keyword(s):  
Quantitative Description ◽  
Rf Sputtering ◽  
Electron Excitation ◽  
Amorphous Semiconductors ◽  
Geometrical Parameters ◽  
Phonon Confinement ◽  
Thermal Electron ◽  
Urbach Tail ◽  
Optical Gap ◽  
Excitation Processes

ABSTRACTIt is usually assumed that optical and electrical properties of amorphous semiconductors are determined by the short-range-order (SRO) parameters of atomic structure. The SRO parameters behavior is considered here as governed by morphology geometrical parameters (MGP) variations. Generalized Skettrup model is developed for a quantitative description of the MGP influence on the density of electron states distribution N(E). Common N(E) relation for the power, exponential and the ‘defect’ regions of the dependence is derived both for adiabatic (optical) and non-adiabatic (thermal) electron excitation processes. The simulated (by the N(E) convolution) spectral dependence of the opti-cal absorption coefficient contains the Tauc, Urbach and the ‘defect’ parts. The optical gap and the Urbach tail slope energies are typical for the ‘device quality’ a-Si:H films at the average morphology geometrical parameters values of order of 1 μm. Nearly linear the optical gap versus the Urbach tail slope energies dependence is obtained at the mor-phology geometrical parameters and temperature changes. Good agreement of experi-mental and the simulation results is achieved for a-Si:H films, prepared both by the RF sputtering and by the silane decomposition.

Valence electron energy loss spectroscopy in reflection geometry

1989 ◽  
Vol 47 ◽  
pp. 378-379
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Energy Loss ◽  
Valence Electron ◽  
Interband Transition ◽  
Specular Reflection ◽  
Three Dimensional ◽  
Electron Excitation ◽  
Transmission Electron ◽  
Yield Information ◽  
Valence Bands ◽  
Excitation Processes

The low energy loss region of a EELS spectrum carries information about the valence electron excitation processes (e.g., collective excitations for free electron like materials and interband transitions for insulators). The relative intensities and the positions of the interband transition energy loss peaks observed in EELS spectra are determined by the joint density of states (DOS) of the initial and final states of the excitation processes. Thus it is expected that EELS in reflection mode could yield information about the perturbation of the DOS of the conduction and valence bands of the bulk crystals caused by the termination of the three dimensional periodicity at the crystal surfaces. The experiments were performed in a Philipps 400T transmission electron microscope operated at 120 kV. The reflection EELS spectra were obtained by a Gatan 607 EELS spectrometer together with a Tracor data acquisition system and the resolution of the spectrometer was about 0.8 eV. All the reflection spectra are obtained from the specular reflection spots satisfying surface resonance conditions.

Narrow optical gap ferroelectric Bi2ZnTiO6 thin films deposited by RF sputtering

2019 ◽  
Vol 7 (17) ◽  
pp. 10696-10701 ◽  
Author(s):  
Fábio G. Figueiras ◽  
J. Ramiro A. Fernandes ◽  
J. P. B. Silva ◽  
Denis O. Alikin ◽  
Eugénia C. Queirós ◽  
...  
Keyword(s):  
Thin Films ◽  
Rf Sputtering ◽  
Optical Gap ◽  
Ferroelectric Oxide

Thriving ferroelectric oxide Bi2ZnTiO6 thin films with a 1.48 eV optical gap.

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.

Surge and Rotating Stall in Axial Flow Compressors—Part II: Experimental Results and Comparison With Theory

1976 ◽  
Vol 98 (2) ◽  
pp. 199-211 ◽  
Author(s):  
E. M. Greitzer
Keyword(s):  
Quantitative Description ◽  
Axial Compressor ◽  
Axial Flow ◽  
Rotating Stall ◽  
Experimental Results ◽  
System Response ◽  
Physical Parameters ◽  
Geometrical Parameters ◽  
Compression System ◽  
Transient System

This paper reports an experimental study of axial compressor surge and rotating stall. The experiments were carried out using a three stage axial flow compressor. With the experimental facility the physical parameters of the compression system could be independently varied so that their influence on the transient system behavior can be clearly seen. In addition, a new data analysis procedure has been developed, using a plenum mass balance, which enables the instantaneous compressor mass flow to be accurately calculated. This information is coupled to the unsteady pressure measurements to provide the first detailed quantitative picture of instantaneous compressor operation during both surge and rotating stall transients. The experimental results are compared to a theoretical model of the transient system response. The theoretical criterion for predicting which mode of compression system instability, rotating stall or surge, will occur is in good accord with the data. The basic scaling concepts that have been developed for relating transient data at different corrected speeds and geometrical parameters are also verified. Finally, the model is shown to provide an adequate quantitative description of the motion of the compression system operating point during the transients that occur subsequent to the onset of axial compressor stall.

A Comparative Study of Hydrogenated Amorphous Silicon Films Prepared by RF Sputtering in He/H2, Ar/H2 and Xe/H2 Mixtures

1986 ◽  
Vol 70 ◽  
Author(s):  
Mark L. Albers ◽  
H. R. Shanks ◽  
J. Shinar
Keyword(s):  
Comparative Study ◽  
Energy Gap ◽  
Rf Sputtering ◽  
Dangling Bond ◽  
Rf Power ◽  
Optical Energy Gap ◽  
Sputtered Films ◽  
Optical Gap ◽  
Hydrogenated Amorphous ◽  
Spin Densities

ABSTRACTPreliminary results of a comparative study of some optical and ESR properties of aSi:H films prepared by rf sputtering on a cold substrate in 10 mtorr of either He, Ar, or Xe and 0.5 mtorr H2 are presented. In all cases the concentration of Si-H and Si-H2 bonds, the optical gap and the dangling bond spin density all generally increase as the rf power is decreased from 3.3 to 0.27 W/cm2. However, whereas the optical energy gap of He/H2 sputtered films ranges from 1.26 eV to 2.13 eV, the gap of Ar/H2 and Xe/H2 films sputtered under these conditions only changes from 1.54 to 1.94 and 1.41 to 1.71 eV, respectively. The dangling bond spin densities are lowest (~1017 cm-3) in the Ar/H2 sputtered films at high rf power and highest (~5x1018 cm-3) in Xe/H2 sputtered films at low power.

Optical Properties of RF-Sputtered a-SiGe:H:O Alloys

1986 ◽  
Vol 77 ◽  
Author(s):  
J. M. T. Pereira ◽  
P. K. Banerjee ◽  
S. S. Mitra
Keyword(s):  
Thin Films ◽  
Refractive Index ◽  
Optical Constants ◽  
Rf Sputtering ◽  
Normal Incidence ◽  
Reflection And Transmission ◽  
Amorphous Thin Films ◽  
Optical Gap ◽  
Transmission Measurements ◽  
Substrate Temperatures

ABSTRACTAmorphous thin films of SixGe1-x:O (x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants (n,k) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 eV and 2.6 eV. The optical gap was derived from the Taue plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of the refractive index and increases the optical gap.

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