States in the Gap of Improved a-Ge:H Studied by Photomodulation Spectroscopy

1991 ◽  
Vol 219 ◽  
Author(s):  
L. Chen ◽  
J. Tauc ◽  
D. Pang ◽  
W. A. Turner ◽  
W. Paul
Keyword(s):  
Glow Discharge ◽  
Valence Band ◽  
Density Of States ◽  
Pump Beam ◽  
Defect Density ◽  
Dangling Bond ◽  
Band Tail ◽  
Valence Bands

ABSTRACTThe photomodulation spectra of a-Ge:H of average photoelectronic quality(ημπ = 1 × 10-10cm2/V) and of improved quality (ημπ = 3 × 10-7cm2/V), produced under different plasma conditions in an r.f. diode reactor by glow discharge, were measured at 80K and are analyzed in analogy with earlier studies of a-Si:H. The spectra of the poorer material are dominated by transitions between dangling bond states and the conduction and valence bands. By contrast, the spectra of the better material require contributions of transitions from the band tail states, indicating that the reduced defect density has resulted in pump-beam induced quasi-Fermi levels reaching near the conduction and valence band edges. A very acceptable fit between plausible density-of-states distributions and the experimental spectra has been found.

Sensitization of the Holes Lifetime by the Addition of Dangling Bonds in a-Si:H

2001 ◽  
Vol 664 ◽  
Author(s):  
L.F. Fonseca ◽  
S. Z. Weisz ◽  
I. Balberg
Keyword(s):  
Valence Band ◽  
Important Implication ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Defect States ◽  
Band Tail ◽  
Present Understanding

ABSTRACTThis paper is concerned with the phenomenon of the increase of the holes lifetime with the increase of the dangling bond concentration in a-Si:H. This rather surprising phenomenon that was observed, but not discussed, previously is shown to be a non-trivial effect which is based on the charged nature of the dangling bonds and a special scenario of the concentrations of the various defect states in the material. The most important implication of our study is that the charged dangling bonds can sensitize the valence band tail states, in contrast with the accepted roles of these types of states. The present understanding suggests that many new interesting phototransport phenomena can be found in a-Si:H.

scholarly journals An Analytical Study on the Local Electronic Density of States of the Valence Bands in Amorphous Silicon Carbide

1998 ◽  
Vol 21 (3) ◽  
pp. 217-219 ◽  
Author(s):  
M. A. Grado-Caffaro ◽  
M. Grado-Caffaro
Keyword(s):  
Silicon Carbide ◽  
Amorphous Silicon ◽  
Valence Band ◽  
Density Of States ◽  
Analytical Study ◽  
Electronic Density ◽  
Amorphous Silicon Carbide ◽  
Electronic Density Of States ◽  
Valence Bands ◽  
Hybrid Orbitals

A formulation for the energy-averaged local valence band density of states of amorphous silicon carbide is derived. To this end,sp3-type hybrid orbitals are employed.

An Alternative Model for the Kinetics of Light-Induced Defects in A-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Paulo V. Santos ◽  
W. B. Jackson ◽  
R. A. Street
Keyword(s):  
Time Dependence ◽  
Valence Band ◽  
Defect Formation ◽  
Defect Density ◽  
Generation Rate ◽  
Band Tail ◽  
Defect Generation ◽  
Wide Range ◽  
Induced Defects ◽  
Kinetics Of

ABSTRACTThe kinetics of light-induced defect generation in a-Si:H was investigated over a wide range of illumination intensities and temperatures. The defect density around 1016cm-3 exhibits a power-law time dependence Ns ∼ G2εfε with ε = 0.2 to 0.3, where G is the photo-carrier generation rate. A model for the kinetics of defect generation is proposed based on the existence of an exponential distribution of defect formation energies in the amorphous network, associated with the valence band tail states. The model reproduces the observed time dependence of the defect density with an exponent e determined by the exponential width of the valence band tail. The temperature dependence of the defect generation rate is well-reproduced by the model, which provides a connection between the Stabler-Wronski effect and the weak-bond model.

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.

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.

Does ion Bombardment Induce a Degradation of the Electronic Properties of a-Si:H Films?

1990 ◽  
Vol 192 ◽  
Author(s):  
P. Roca i Cabarrocas ◽  
P. Morin ◽  
J. Conde ◽  
V. Chu ◽  
J.Z. Liu ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Electronic Properties ◽  
Valence Band ◽  
Ion Bombardment ◽  
Clear Correlation ◽  
Negative Bias ◽  
Substrate Bias ◽  
Band Tail ◽  
Ion Energy

ABSTRACTWe present a detailed study of the effects of a negative bias applied to the substrate on the electronic properties of a-Si:H films deposited by r.f. glow discharge. Two series of samples deposited at 30 and 100 mTorr respectively have been studied. For each series the negative d.c. bias applied to the substrate was decreased from 0 to −100 V in steps of 25 V. We observe for both series of samples an improvement of the electronic properties of the films as we decrease the substrate bias (increase the ion energy) down to − 50 V. We have found a clear correlation between the negative bias applied to the substrate and the subgap absorption, the valence band tail slope and the electron and hole μτ products.

Capacitance Studies of Light-Induced Effects in Undoped Hydrogenated Amorphous Silicon

1985 ◽  
Vol 49 ◽  
Author(s):  
K. Zellama ◽  
J.D. Cohen ◽  
J.P. Harbison
Keyword(s):  
Electrical Conductivity ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Light Saturation ◽  
Band Tail ◽  
Bond Density ◽  
Induced Changes ◽  
Hydrogenated Amorphous

AbstractThe effects of light saturation on the properties of undoped a-Si:H films were studied by a new capacitance profiling technique which can be used to directly determine changes in the dangling bond density of states near midgap. Coplanar conductivity and capacitance vs. temperature measurements save the changes in activation energies for electrical conductivity. These studies indicate that, while substantial increases in the dangling bond densities are observed for most samples, the detailed behavior of the light induced changes in these films are inconsistent with the creation of such defects by breaking weak valence band tail states.

THE STUDY OF SURFACE SEGREGATION, STRUCTURE, AND VALENCE BAND DENSITY OF STATES OF Pt3Ni(100), (110), AND (111) CRYSTALS

2006 ◽  
Vol 13 (05) ◽  
pp. 697-702 ◽  
Author(s):  
B. S. MUN ◽  
M. WATANABE ◽  
M. ROSSI ◽  
V. STAMENKOVIC ◽  
N. M. MARKOVIC ◽  
...  
Keyword(s):  
Single Crystals ◽  
Valence Band ◽  
Density Of States ◽  
Surface Segregation ◽  
Low Energy ◽  
Ion Scattering ◽  
Low Energy Ion Scattering ◽  
Low Energy Electron ◽  
Valence Bands ◽  
Segregation Structure

The surface segregation, structure, and valence band density of states of Pt 3 Ni (100), (110), and (111) single crystals are characterized with low energy ion scattering (LEIS), low energy electron diffraction (LEED), and ultraviolet photoemission spectroscopy (UPS). The results of LEIS clearly reveal the complete surface segregation of Pt to the top layer on all crystal alloys. LEED indicates the (5 × 1) surface reconstruction on the Pt 3 Ni (100), while (110) and (111) surfaces show (2 × 1) and (1 × 1) patterns, respectively, identical to Pt single crystals. The valence bands density of states on Pt 3 Ni alloys are compared to those of Pt single crystals via UPS measurements.

Material Properties of a-SiGe:H Solar Cells as a Function of Growth Rate

2010 ◽  
Vol 1245 ◽  
Author(s):  
Peter Hugger ◽  
JinWoo Lee ◽  
J. David Cohen ◽  
Guozhen Yue ◽  
Xixiang Xu ◽  
...  
Keyword(s):  
Valence Band ◽  
Material Properties ◽  
Defect Density ◽  
Schottky Contact ◽  
Drive Level ◽  
Measurement Methods ◽  
Device Performance ◽  
Band Tail ◽  
Contact Devices ◽  
Defect Densities

AbstractWe have examined a series of a Si,Ge:H alloy devices deposited using both RF and VHF glow discharge in two configurations: SS/n+/i (a-SiGe:H)/p+/ITO nip devices and SS/n+/i (a-SiGe:H)/Pd Schottky contact devices, over a range of deposition rates. We employed drive-level capacitance profiling (DLCP), modulated photocurrent (MPC), and transient junction photo-current (TPI) measurement methods to characterize the electronic properties in these materials. The DLCP profiles indicated quite low defect densities (mid 1015 cm-3. to low 1016 cm-3 depending on the Ge alloy fraction) for the low rate RF (∼1Å/s) deposited a-SiGe:H materials. In contrast to the RF process, the VHF deposited a-SiGe:H materials did not exhibit nearly as rapid an increase of defect density with the deposition rate, remaining well below 1017 cm-3. up to rates as high as 10Å/s. Simple examination of the TPI spectra on theses devices allowed us to determine valence band-tail widths.. Modulated photocurrent (MPC) obtained for several of these a-SiGe:H devices allowed us to deduce the conduction band-tail widths. In general, the a-Si,Ge:H materials exhibiting narrower valence band-tail widths and lower defect densities correlated with the best device performance.

Hydrogen Density of States and Defects Densities in a-Si:H

1996 ◽  
Vol 420 ◽  
Author(s):  
S C Deane ◽  
M J Powell ◽  
J Robertson
Keyword(s):  
Valence Band ◽  
Density Of States ◽  
Unified Model ◽  
Band Tail ◽  
Hydrogen Density ◽  
The Creation

AbstractFurther details are given of a unified model of the hydrogen density of states and defect pool of a-Si:H. The model is compared to other defect models and extended to describe a-Si alloys and the creation of valence band tail states during growth.

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