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.

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.

Investigations of Tail and Defect States in a-Si0.6Ge0.4:H Alloys by PDS and ESR - Implications for the Interaction of Weak and Dangling Bonds

1995 ◽  
Vol 377 ◽  
Author(s):  
Tilo P. Drüsedau ◽  
Andreas N. Panckow ◽  
Bernd Schröder
Keyword(s):  
Silicon Germanium ◽  
Defect Density ◽  
State Density ◽  
Model Parameters ◽  
Defect States ◽  
Conversion Model ◽  
Order Of Magnitude ◽  
Underlying Mechanisms ◽  
Amorphous Silicon Germanium ◽  
Excess Absorption

ABSTRACTInvestigations on the gap state density were performed on a variety of samples of hydrogenated amorphous silicon germanium alloys (Ge fraction around 40 at%) containing different amounts of hydrogen. From subgap absorption measurements the values of the “integrated excess absorption” and the “defect absorption” were determined. Using a calibration constant, which is well established for the determination of the defect density from the integrated excess absorption of a-Si:H and a-Ge:H, it was found that the defect density is underestimated by nearly one order of magnitude. The underlying mechanisms for this discrepancy are discussed. The calibration constants for the present alloys are determined to 8.3×1016 eV−1 cnr2 and 1.7×1016 cm−2 for the excess and defect absorption, respectively. The defect density of the films was found to depend on the Urbach energy according to the law derived from Stutzmann's dangling bond - weak bond conversion model for a-Si:H. However, the model parameters - the density of states at the onset of the exponential tails N*=27×1020 eV−1 cm−3 and the position of the demarcation energy Edb-E*=0.1 eV are considerably smaller than in a-Si:H.

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.

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.

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 Valence Band Tail Density of States and Bond Angle Distortion in a-SiNx: H Alloys

1996 ◽  
Vol 426 ◽  
Author(s):  
B. G. Budaguan ◽  
A. A. Aivazov ◽  
D. A Stryahilev
Keyword(s):  
Infrared Spectroscopy ◽  
Valence Band ◽  
Bond Angle ◽  
Deformation Energy ◽  
Essential Difference ◽  
Band Tail ◽  
Characteristic Energy ◽  
Valence States ◽  
Bond Bending ◽  
Scattering Characteristic

AbstractFilms of a-SiNx:H with x = 0.0..0.62 were deposited by glow discharge decomposition of (10% SiH4+90%/H2 )+ NH3 mixture. The chemical bonding and composition of films were investigated with using of infrared spectroscopy. The deformation energy per Si atom connected to bond bending Vkθ was calculated from data of Raman scattering. Characteristic energy of valence band tail (VBT) states distribution, E0v, were determined fromrsubgap absorption spectra. The dependencies of E0v and Vkθ on film composition, x, were considered in order to estimate the influence of the bond angle disorder on the distribution of VBT states.The essential difference in behavior of E0v and Vkθ dependencies on x was found for Si-rich (x<0. 15) alloys. When Vkθ value increase with x, the E0v parameter stays almost constant; while at x>0. 15 the E0v increase with x as well as the VKO. It means that bond angle disorder in the bulk of the material contributes to VBT characteristic energy, but it is not the only source. Another factors as it was shown may be connected with valence states of Si atoms, localized near inner boundaries.

Examination of the Defect Pool Model by An Improved Analysis of the Constant Photocurrent Method

1995 ◽  
Vol 377 ◽  
Author(s):  
Helmut Stiebig ◽  
Frank Siebke
Keyword(s):  
Valence Band ◽  
Defect Density ◽  
Localized States ◽  
Optical Transitions ◽  
Defect States ◽  
Band Tail ◽  
Defect Distribution ◽  
Density Of Localized States ◽  
Pool Model ◽  
Extended States

ABSTRACTWe have developed an improved analysis of constant photocurrent method (CPM) data. It is based on a numerical simulation of CPM spectra taking into account the full set of optical transitions between localized and extended states, capture and emission processes as well as the position of the Fermi level. Comparing measured and simulated CPM spectra provides information about the density of localized states in a-Si:H, i.e. the valence band tail, the integrated defect density, the energy distribution and the charge state of defect states. Based on these results we examine the predictions of the defect-pool model. The defect distribution in undoped and doped a-Si:H can be described by the defect-pool model taking into account the doping level dependence of principal parameters including the valence band tail, the equilibration temperature, and the width of the defect-pool.

Direct Plan View FIB Liftout for Near-Surface Defect Analysis in TEM

2013 ◽  
Author(s):  
Max L. Lifson ◽  
Carla M. Chapman ◽  
D. Philip Pokrinchak ◽  
Phyllis J. Campbell ◽  
Greg S. Chrisman ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Silicon Germanium ◽  
Focused Ion Beam ◽  
Surface Defects ◽  
Ion Beam ◽  
Misfit Dislocations ◽  
Tem Analysis ◽  
Plan View ◽  
Near Surface ◽  
Straightforward Method

Abstract Plan view TEM imaging is a powerful technique for failure analysis and semiconductor process characterization. Sample preparation for near-surface defects requires additional care, as the surface of the sample needs to be protected to avoid unintentionally induced damage. This paper demonstrates a straightforward method to create plan view samples in a dual beam focused ion beam (FIB) for TEM studies of near-surface defects, such as misfit dislocations in heteroepitaxial growths. Results show that misfit dislocations are easily imaged in bright-field TEM and STEM for silicon-germanium epitaxial growth. Since FIB tools are ubiquitous in semiconductor failure analysis labs today, the plan view method presented provides a quick to implement, fast, consistent, and straightforward method of generating samples for TEM analysis. While this technique has been optimized for near-surface defects, it can be used with any application requiring plan view TEM analysis.

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