Band Tails and Thermal Disorder in Doped and Undoped Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys

1990 ◽  
Vol 192 ◽  
Author(s):  
Samer Aljishi ◽  
J. David Cohen ◽  
Shu Jin ◽  
Lothar Ley
Keyword(s):  
Valence Band ◽  
Conduction Band ◽  
Photoelectron Spectroscopy ◽  
Silicon Germanium ◽  
Total Yield ◽  
Structural Disorder ◽  
Band Tail ◽  
Characteristic Energy ◽  
Densities Of States ◽  
Thermal Disorder

ABSTRACTThe energy distribution and temperature dependence of the conduction and valence band tail density of states in a-Si:H and a-Si,Ge:H alloys is determined via total yield photoelectron spectroscopy. All films are observed to possess purely exponential conduction and valence band tail densities of states; however, the characteristic energy of the conduction band tail increases much more rapidly with temperature in the range of 300K to 550K than that of the valence band tail. This indicates that over that temperature range the conduction band tail is considerably more susceptible to thermal disorder than to structural disorder whereas the reverse holds for the valence band tail.

Thermal Equilibration Between Band Tail and Near Surface Defect States in Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys

1990 ◽  
Vol 192 ◽  
Author(s):  
Samer Aljishi ◽  
Shu Jin ◽  
Lothar Ley ◽  
Sigurd Wagner
Keyword(s):  
Valence Band ◽  
Photoelectron Spectroscopy ◽  
Silicon Germanium ◽  
Total Yield ◽  
State Density ◽  
Defect States ◽  
Band Tail ◽  
Characteristic Energy ◽  
Near Surface ◽  
Average Value

ABSTRACTWe employ total yield photoelectron spectroscopy to measure the density of occupied states at the clean a-SixGe1_x:H alloy surface. The near surface defect states are observed to lie at 0.57 eV above the valence band edge with a density of 4×l017 cm−3, independent of Ge content. The valence band tail characteristic energy is also measured to be independent of alloy composition with an average value of 54 meV. We demonstrate that thermodynamic equilibrium at the surface between weak bonds (forming the valence band tail) and the dangling bonds provides an excellent description of the experimental data and explains why the surface state density in a-Si:H cannot be lowered below the 1011 to 1012 cm−2 range.

Photoluminescence in Hydrogenated Silicon-Germanium Alloys

1987 ◽  
Vol 95 ◽  
Author(s):  
R. Ranganathan ◽  
M. Gal ◽  
J. M. Viner ◽  
P. C. Taylor
Keyword(s):  
Valence Band ◽  
Conduction Band ◽  
Silicon Germanium ◽  
Low Energy ◽  
Dangling Bond ◽  
Band Tail ◽  
Hydrogenated Silicon ◽  
Bond State ◽  
Constant Magnitude ◽  
Low Energy Tail

AbstractResults of a detailed study of photoluminescence (PL) in the a-Si1−xGex:H system are presented. Many samples exhibit a low energy “tail” to the PL efficiency which is of constant magnitude independent of x. There is a departure from this behavior when a low energy PL peak near 0.8–0.9 eV is present. The position of the low energy PL peak is independent of Ge concentration. It has been suggested that this PL transition is from an electron in the conduction band tail into a silicon dangling bond state. As Ge is added to a-Si:H it is the edge of the conduction band which decreases in energy while the valence band remains relatively constant in energy. It is therefore unlikely that the low energy PL is due to a transition from the conduction band into a silicon dangling bond state because the energy of the silicon dangling bond with respect to the valence band is probably essentially independent of Ge content. If the PL which peaks near 0.8 eV results from a transition which involves a silicon dangling bond, then the transition may be from the dangling bond to the valence band.

The Density of States in Undoped and Doped Amorphous Silicon-Germanium Alloys Determined through Photoyield Spectroscopy

1989 ◽  
Vol 149 ◽  
Author(s):  
S. Aljishi ◽  
Jin Shu ◽  
L. Ley
Keyword(s):  
Valence Band ◽  
Density Of States ◽  
Relative Position ◽  
Silicon Germanium ◽  
Lower Energy ◽  
Composition Range ◽  
Significant Shift ◽  
Band Tail ◽  
Defect Band ◽  
Amorphous Silicon Germanium

ABSTRACTPhotoelectron yield spectroscopy is used to study the occupied density of states (DOS) in undoped and doped a-Si, Ge:H alloys. We find a shift in the top of the valence band to lower energy as the Ge content is increased. The width of the defect band becomes abruptly narrower when Ge is initially introduced. This change is accompanied by a significant shift in the relative position of the Fermi level towards midgap. The defect peak tracks the valence band throughout the entire composition range. The intrinsic valence band tail in the alloys is found to be an exponential with a characteristic slope of 50 to 60 meV independent of composition. Boron and phosphorous doping affect the DOS of the alloys in a manner similar to that measured in a-Si:H.

Highly Sensitive Analysis for Valence Band Edge of C60 Films by Total Yield Photoelectron Spectroscopy

1994 ◽  
Vol 349 ◽  
Author(s):  
S. Gonda ◽  
M. Kawasaki ◽  
T. Arakane ◽  
H. Koinuma
Keyword(s):  
Valence Band ◽  
Photoelectron Spectroscopy ◽  
Total Yield ◽  
Kelvin Probe ◽  
Highly Sensitive ◽  
Gap States ◽  
Kelvin Probe Method ◽  
C60 Films ◽  
Simple Picture

ABSTRACTWe have in-situ measured the density of states (DOS) around the top of valence band of pristine C60 films by means of total yield photoelectron spectroscopy. The top of valence band (TVB) of C60 was located at 5.00eV below the vacuum level. Considerable amplitude of gap states was observed up to 0.9eV above the TVB. Kelvin probe method revealed that the Fermi level of amorphous C60 film was located at 0.47eV above the TVB. The improvement of crystallinity in C60 films, which induced the increase in electrical conductivity as well, increased the DOS above the TVB. The electric conduction of C60 films cannot be explained with a simple picture for carrier conduction in semiconductors.

scholarly journals Velocity Map Imaging VUV Angle-Resolved Photoelectron Spectroscopy of Isolated Silver Sulfide Nanoparticles

2021 ◽  
Author(s):  
Danijela Danilović ◽  
Dusan Bozanic ◽  
Gustavo A. Garcia ◽  
Laurent Nahon ◽  
Una Stamenović ◽  
...  
Keyword(s):  
Valence Band ◽  
Conduction Band ◽  
Photoelectron Spectroscopy ◽  
Minimum Energy ◽  
Aqueous Dispersion ◽  
Silver Sulfide ◽  
Valence Band Maximum ◽  
Maximum Energy ◽  
Velocity Map Imaging ◽  
Silver Sulfide Nanoparticles

Abstract The angle-resolved photoelectron spectroscopy of isolated silver sulfide nanoparticles was carried out by using velocity map imaging technique at the DESIRS beamline of SOLEIL synchrotron facility. The reported spectroscopy results were obtained after interaction of the synchrotron radiation with a polydisperse aerosol produced from aqueous dispersion of silver sulfide particles, approximately 16 nm in diameter. The photoelectron and UV-Vis-NIR absorption spectra were used to estimate the maximum energy of the valance- and the minimum energy of the conduction-band of the nanoparticles. With respect to the vacuum level, the obtained values were found to be 5.5±0.1 eV and 4.5±0.1 eV for the valence band maximum and conduction band minimum, respectively. The dependence of the asymmetry parameter on the electron energy along the silver sulfide valence band showed an onset of inelastic scattering at ~1 eV electron kinetic energy.

scholarly journals Photocatalytical Properties and Theoretical Analysis of N, Cd-Codoped TiO2Synthesized by Thermal Decomposition Method

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Hongtao Gao ◽  
Bing Lu ◽  
Fangfang Liu ◽  
Yuanyuan Liu ◽  
Xian Zhao
Keyword(s):  
Thermal Decomposition ◽  
Theoretical Analysis ◽  
Valence Band ◽  
Conduction Band ◽  
Photoelectron Spectroscopy ◽  
Decomposition Method ◽  
Density Functional ◽  
X Ray ◽  
Thermal Decomposition Method ◽  
Bet Specific Surface Area

N, Cd-codoped TiO2have been synthesized by thermal decomposition method. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-visible diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) specific surface area analysis, respectively. The products represented good performance in photocatalytic degradation of methyl orange. The effect of the incorporation of N and Cd on electronic structure and optical properties of TiO2was studied by first-principle calculations on the basis of density functional theory (DFT). The impurity states, introduced by N 2p or Cd 5d, lied between the valence band and the conduction band. Due to dopants, the band gap of N, Cd-codoped TiO2became narrow. The electronic transition from the valence band to conduction band became easy, which could account for the observed photocatalytic performance of N, Cd-codoped TiO2. The theoretical analysis might provide a probable reference for the experimentally element-doped TiO2synthesis.

Electron Transport and Conduction-Band-Tail States in a-Si:H Deposited with a Remote Hydrogen Plasma

1993 ◽  
Vol 297 ◽  
Author(s):  
C.E. Nebel ◽  
R.A. Street ◽  
N.M. Johnson ◽  
J. Walker
Keyword(s):  
Electron Transport ◽  
Conduction Band ◽  
Defect Density ◽  
Plasma Deposition ◽  
Hydrogen Plasma ◽  
Band Tail ◽  
Mobility Edge ◽  
Characteristic Energy ◽  
Tail State ◽  
Electron Transport Properties

Electron transport properties of a-Si:H prepared in a remote hydrogen plasma deposition reactor (RHPD) at TD = 400°C were investigated in the temperature regime 110 K ≤ T ≤ 300 K by time-of-flight and post-transit spectroscopy experiments. Based on these data the conduction-band-tail state distribution was calculated. In the energy range 85 meV ≤ Ec- E ≤ 350 meV below the mobility edge Ec the tail is well described by an exponential distribution with a characteristic energy of ≃ 21 meV. Deeper in the mobility gap (Ec-E > 350 meV) the tail smoothly passes over into the defect density which is approximately six orders of magnitude smaller than at the mobility edge. Comparisons with data deduced on conventionally prepared a-Si:H (RF-, DC-glow discharge) at TD = 230 °C show that electron transport and the conduction band tail of the RHPD material are comparable.

XPS Spectra and Optical Reflectivity of Yttrium Stabilised Zirconia

1992 ◽  
Vol 293 ◽  
Author(s):  
P. Camagni ◽  
L.E. Depero ◽  
F. Parmigiani ◽  
G. Samoggia ◽  
L. Sangaletri ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Synchrotron Radiation ◽  
Energy Range ◽  
Single Crystals ◽  
Valence Band ◽  
Conduction Band ◽  
Photoelectron Spectroscopy ◽  
Electron Excitation ◽  
Xps Spectra ◽  
X Ray

AbstractX-ray photoelectron spectroscopy measurements and synchrotron radiation reflectivity and measurements in the photon energy range between 5eV and 30 eV are reported for yttrium stabilised zirconia single crystals. From the present data some behaviour of the valence band and conduction band electronic structure are elucidated. Two features present in the valence band XPS spectra, not explained on the basis of one-clectron theory, are tentatively assigned to simultaneous two electron excitation.

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