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.

Subband Recombination in a-Si:H

1992 ◽  
Vol 258 ◽  
Author(s):  
S.Q. Gu ◽  
P.C. Taylor
Keyword(s):  
Excitation Energy ◽  
Valence Band ◽  
Low Temperatures ◽  
Strong Dependence ◽  
Low Energy ◽  
Band Tail ◽  
Low Energy Tail

ABSTRACTPhotoluminescence (PL) in a-Si:H has been studied as a function of excitation energy from above the gap down to well below the gap. Although the width of the PL peak shows no strong dependence on the excitation energy at low temperatures, the low energy tail of bandtail PL exhibits an approximately exponential drop with decreasing energy, I ≈ exp(hν/δE), where δE increases with decreasing excitation energy for excitation energy below about 1.65 eV. This behavior is attributed to the slow downward hopping of holes in the valence band tail that are generated below a thermalization threshold at low temperatures.

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.

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.

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.

Microstructure and Dangling Bond Defects in Amorphous Hydrogenated Silicon Deposited Near Room Temperature

1992 ◽  
Vol 258 ◽  
Author(s):  
Man Ken Cheung ◽  
Mark A. Petrich
Keyword(s):  
Room Temperature ◽  
Dangling Bond ◽  
Optimum Conditions ◽  
Band Tail ◽  
Hydrogenated Silicon ◽  
Photothermal Deflection Spectroscopy ◽  
Amorphous Hydrogenated Silicon ◽  
Photothermal Deflection ◽  
Substrate Temperatures ◽  
Absorption Measurements

ABSTRACTThe microstructure of high-density amorphous hydrogenated silicon (a-S.i:H) films deposited at 50°C substrate temperature was revealed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies to be similar to that of “device-quality” a-Si:H films deposited at standard “optimum” conditions. However, optical absorption measurements of these low microstructure 50°C films with photothermal deflection spectroscopy indicate that they have higher densities of gap state defects and localized band tail states than “device-quality” films deposited at standard substrate temperatures. The correlation between the amount of microstructure and electronic properties is not unique. A low amount of microstructure is a necessary, but not sufficient, requirement for high electronic quality a-Si:H films.

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.

Low energy shifted photoluminescence of Er3+ incorporated in amorphous hydrogenated silicon–germanium alloys

2009 ◽  
Vol 355 (16-17) ◽  
pp. 976-981 ◽  
Author(s):  
E. López-Luna ◽  
M.A. Vidal ◽  
A.G. Rodríguez ◽  
H. Navarro-Contreras ◽  
Y. Kudriavtsev ◽  
...  
Keyword(s):  
Silicon Germanium ◽  
Low Energy ◽  
Hydrogenated Silicon ◽  
Amorphous Hydrogenated Silicon ◽  
Silicon Germanium Alloys

Transient Photoconductivity Study of the Distribution of Gap States in 100°C VHF-deposited Hydrogenated Silicon Layers

2008 ◽  
Vol 1066 ◽  
Author(s):  
Monica Brinza ◽  
Guy J. Adriaenssens ◽  
Jatindra K. Rath ◽  
Ruud E.I. Schropp
Keyword(s):  
Energy Distribution ◽  
Conduction Band ◽  
Conduction Band Edge ◽  
Dangling Bond ◽  
Hydrogenated Silicon ◽  
Transient Photocurrent ◽  
Transient Photoconductivity ◽  
Continuous Background ◽  
Transport Path ◽  
Gap States

ABSTRACTThe energy distribution of gap states has been examined by means of transient photocurrent measurements in a series of 100°C VHF-deposited Si:H samples that spans the amorphous to microcrystalline transition. The ‘amorphous’ distribution, consisting of a continuous background and a prominent dangling-bond-induced peak, remains largely intact across the transition. The transport path located at the conduction band edge in a-Si:H, some 0.63 eV above the dangling bond D− energy, moves down to ∼0.55 eV above the corresponding D− level in the microcrystalline samples.

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