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.

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.

Theoretical and X-ray spectral investigations of density of states in amorphous silicon-germanium layers

1987 ◽  
Vol 90 (1-3) ◽  
pp. 127-130
Author(s):  
E.P. Domashevskaya ◽  
E.N. Desyatirikova ◽  
A.F. Khokhlov ◽  
V.A. Terekhov ◽  
Yu.K. Timoshenko
Keyword(s):  
Amorphous Silicon ◽  
Density Of States ◽  
Silicon Germanium ◽  
X Ray ◽  
Amorphous Silicon Germanium

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.

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.

Electronic Transport and the Density of States Distribution in a-(Si, Ge):H, F Alloys

1986 ◽  
Vol 70 ◽  
Author(s):  
S. Aljishi ◽  
Z E. Smith ◽  
D. Slobodin ◽  
J. Kolodzey ◽  
V. Chu ◽  
...  
Keyword(s):  
Optical Properties ◽  
Glow Discharge ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Electronic Transport ◽  
Silicon Germanium ◽  
Drift Mobility ◽  
Electronic And Optical Properties ◽  
Reported Data ◽  
Amorphous Silicon Germanium

ABSTRACTThe electronic and optical properties of amorphous silicon-germanium alloys produced by d.c. and r.f. glow discharge are reported. Data on the sub-gap absorption, dark and photo conductivities, drift mobilities and drift mobility-lifetime products are used to propose a density of states model.

Dependence of the Electronic Properties of Hot-Wire CVD Amorphous Silicon-Germanium Alloys on Oxygen Impurity Levels

2007 ◽  
Vol 989 ◽  
Author(s):  
Shouvik Datta ◽  
J. David Cohen ◽  
Yueqin Xu ◽  
A. H. Mahan ◽  
Howard M. Branz
Keyword(s):  
Amorphous Silicon ◽  
Valence Band ◽  
Silicon Germanium ◽  
Oxygen Impurity ◽  
Hot Wire ◽  
Defect Level ◽  
Related Defect ◽  
Amorphous Silicon Germanium ◽  
Oxygen Impurities ◽  
Silicon Germanium Alloys

AbstractWe report the effects of intentionally introducing up to ∼ 5×1020/cm3 oxygen impurities into hydrogenated amorphous silicon-germanium alloys (of roughly 30at.% Ge) grown by the hot-wire chemical vapor deposition (HWCVD) method. Deep defect densities determined by drive-level capacitance profiling (DLCP) indicated a modest increase with increasing oxygen content (up to a factor of 3 at the highest oxygen level). Transient photocapacitance (TPC) spectra indicated a clear spectral signature for an optical transition between the valence band and an additional defect level which is attributed to oxygen impurities. The oxygen impurity related defect transition has an optical threshold around 1.4eV above the valence band and also results in a negative contribution to the TPC signal. This initially led us to believe that the bandtail for the higher oxygen samples was much narrower than it actually is. Surprisingly, this additional oxygen related defect level appears to have only a very minor effect upon the estimated minority carrier collection fraction. The effects of light-induced degradation upon some of these oxygen contaminated samples were also examined. We infer the existence of a significant thermal barrier to explain the observed spectral signatures of this oxygen impurity defect.

Density of states in the pseudo‐gap of amorphous silicon‐germanium alloys from electrical and optical measurements

1992 ◽  
Vol 60 (12) ◽  
pp. 1465-1467 ◽  
Author(s):  
T. Pisarkiewicz ◽  
A. Kolodziej ◽  
E. Schabowska‐Osiowska ◽  
T. Stapinski ◽  
A. Rodzik ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Density Of States ◽  
Silicon Germanium ◽  
Optical Measurements ◽  
Amorphous Silicon Germanium ◽  
Silicon Germanium Alloys

Photoemission Studies of Amorphous Silicon/Germanium Heterojunctions

1985 ◽  
Vol 49 ◽  
Author(s):  
F. Evangelisti ◽  
S. Modesti ◽  
F. Boscherini ◽  
P. Fiorini ◽  
C. Quaresima ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Amorphous Silicon ◽  
Valence Band ◽  
Silicon Germanium ◽  
Interface Formation ◽  
Band Bending ◽  
Amorphous Silicon Germanium ◽  
Synchrotron Radiation Photoemission ◽  
Valence Band Discontinuity

AbstractThe heterostructures obtained by growing a-Ge on a-Si:H and a-Si have been investigated by synchrotron radiation photoemission. We measured valence band and core level spectra on the heterostructures grown in situ under ultrahigh-vacuum conditions. A step-by-step monitoring of possible band-bending changes during the interface formation enabled us to determine unambiguously the band discontinuities. The measured values of the valence band discontinuity were 0.2 ± 0.1 eV for a-Si:H/a-Ge and 0.0 ± 0.1 eV for a-Si/a-Ge, respectively. Evidence was found for the formation of abrupt interfaces without interdiffusion.

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