Defect-Related Photoluminescence of a-Si:H

1994 ◽  
Vol 336 ◽  
Author(s):  
Isabell Ulber ◽  
Axel Barth ◽  
Walther Fuhs ◽  
Helmut Mell
Keyword(s):  
Density Of States ◽  
Local Structure ◽  
Defect Density ◽  
Light Exposure ◽  
Electron Bombardment ◽  
Defect States ◽  
Phosphorus Doping ◽  
Radiative Process ◽  
Radiative Center ◽  
Measured Density

ABSTRACTThe defect-related photoluminescence (0.8–0.9eV) of a-Si:H is studied as a function of the defect density ND and the temperature using subgap excitation of Ex= 1.16eV. Electron bombardment, light exposure and phosphorus doping were employed to create defects. The defect density ND was infered from CPM- and PDS-spectroscopy. We conclude from the measured density-of-states distributions of doped films that the radiative process is tunneling of bandtail carriers (Majority carriers) into the defect states. The dependence of the emission intensity on ND suggests that only a subgroup of the defects acts as radiative center. We propose that the local structure of the defect determines whether it acts as radiative or nonradiative center.

Density of States in Tritiated Amorphous Silicon Measured Using CPM

2004 ◽  
Vol 836 ◽  
Author(s):  
Simone Pisana ◽  
Stefan Costea ◽  
Tome Kosteski ◽  
Nazir P. Kherani ◽  
Stefan Zukotynski ◽  
...  
Keyword(s):  
Thin Films ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Defect Density ◽  
Main Type ◽  
Electronic States ◽  
Conduction Band Edge ◽  
Dangling Bond ◽  
Defect States ◽  
Silicon Thin Films

ABSTRACTThe constant photocurrent method has been used to obtain the density of occupied electronic states of tritiated amorphous silicon thin films. The analyses showed a peak of defects located 1.24 eV below the conduction band edge, suggesting that the main type of defect present in the films was a doubly occupied dangling bond. The concentration of defect states increases as a result of tritium decay by about two orders of magnitude over a period of 500 hours. The defect density in the tritiated amorphous silicon samples could be reduced by thermal annealing, after which it increased once more.

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.

Dependence of the a-Si:H Defect Density of States on the Magnetic Field Profile of an Electron Cyclotron Resonance Microwave Plasma

1992 ◽  
Vol 258 ◽  
Author(s):  
F.S. Pool ◽  
J.M. Essick ◽  
Y.H. Shing ◽  
R.T. Mather
Keyword(s):  
Magnetic Field ◽  
Density Of States ◽  
Cyclotron Resonance ◽  
Electron Cyclotron Resonance ◽  
Microwave Plasma ◽  
Defect Density ◽  
Electron Cyclotron ◽  
Field Profile ◽  
Magnetic Field Profile ◽  
The Magnetic Field

ABSTRACTThe magnetic field profile of an electron cyclotron resonance (ECR) microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. Films of a-Si:H were deposited at pressures of 0.7 mTorr and 5 mTorr with a H2/SiH4 ratio of approximately three. The mobility gap density of states ND, deposition rate and light to dark conductivity were determined for the a-Si:H films. This data was correlated to the magnetic field profile of the plasma, which was characterized by Langmuir probe measurements of the ion current density. By variation of the magnetic field profile ND could be altered by more than an order of magnitude, from 1×1016 to 1×1017 at 0.7 mTorr and 1×1016 to 5×1017 at 5 mTorr. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration.

scholarly journals Ab initioStudies of Electronic Structure of Defects in PbTe

2005 ◽  
Vol 864 ◽  
Author(s):  
Salameh Ahmad ◽  
Daniel Bilc ◽  
S.D. Mahanti ◽  
M.G. Kanatzidis
Keyword(s):  
Electronic Structure ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
Resonance State ◽  
Interesting Case ◽  
The Other ◽  
Defect States ◽  
Strong Resonance ◽  
Structure Calculations

AbstractAb initioelectronics structure calculations have been carried out in a series of RPb2n-1Te2n, n=16, compounds to understand the nature of “defect” states introduced by R where R = vacancy, monovalent Na, K, Rb, Cs, Ag atoms and divalent Cd atoms. We find that the density of states (DOS) near the top of the valence band and the bottom of the conduction band get significantly modified. The Na atom seems to perturb this region least (ideal acceptor in PbTe) and the other monovalent atoms enhance the DOS near the top of the valence band. Cd is an interesting case, since it introduces a strong resonance state near the bottom of the conduction band.

The Effects of Hydrogen Profiling and of Light-Induced Degradation on the Electronic Properties of Hydrogenated Nanocrystalline Silicon

2005 ◽  
Vol 862 ◽  
Author(s):  
A.F. Halverson ◽  
J.J. Gutierrez ◽  
J.D. Cohen ◽  
Baojie Yan ◽  
Jeffrey Yang ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Minority Carrier ◽  
Defect Density ◽  
Light Exposure ◽  
Nanocrystalline Silicon ◽  
Drive Level ◽  
Dramatic Decrease ◽  
Transient Photocurrent ◽  
Hydrogen Dilution ◽  
Carrier Collection

AbstractThe electronic properties of hydrogenated nanocrystalline silicon (nc-Si:H) were studied using junction capacitance methods. Drive-level capacitance profiling (DLCP) measurements revealed significant differences for nc-Si:H layers deposited under constant hydrogen dilution compared to those deposited using hydrogen profiling, with lower DLCP densities in the latter case. Transient photocapacitance (TPC) measurements revealed the mixed-phase nature of these materials. It disclosed spectra that appeared quite microcrystalline-like at lower temperatures, but more similar to a-Si:H at higher temperatures where the minority carrier collection is higher in the nanocrystalline component of these samples. This then suppresses the TPC signal from this component compared to the a-Si:H component. In contrast, because transient photocurrent signals are enhanced by the additional minority carrier collection, those spectra appear microcrystalline like at all temperatures. We also investigated the effects of light-induced degradation in these devices. This caused a dramatic decrease in hole collection, similar to that caused by reducing the measurement temperature of the samples. However, the light exposure did not appear to increase the deep defect density (dangling bonds).

The effects of sub-bandgap transitions and the defect density of states on the photocurrent response of a single ZnO-coated silica nanospring

2020 ◽  
Vol 32 (3) ◽  
pp. 035202
Author(s):  
Peter M Wojcik ◽  
Lyndon D Bastatas ◽  
Negar Rajabi ◽  
Pavel V Bakharev ◽  
David N McIlroy
Keyword(s):  
Density Of States ◽  
Defect Density ◽  
Photocurrent Response

Electronic Defects and Device Performance in CuGaSe2 Solar Cells

2007 ◽  
Vol 1012 ◽  
Author(s):  
J. Jedediah Rembold ◽  
Todd W. Curtis ◽  
Jennifer T. Heath ◽  
David L. Young ◽  
Steve W. Johnston ◽  
...  
Keyword(s):  
Solar Cells ◽  
Defect Density ◽  
Wide Bandgap ◽  
Device Performance ◽  
Defect States ◽  
Materials Properties ◽  
Interface Recombination ◽  
Interface Defect ◽  
Limited Supply ◽  
Electronic Defects

AbstractThe electronic and materials properties of two series of wide-bandgap solar cells with Cu-poor CuGaSe2 (CGS) absorbers have been studied, to better understand limitations on the device performance. One series of samples displayed distinct lateral non-uniformities in Cu/Ga ratio, Na content, and thickness, likely due to a limited supply of Se during CGS growth. The second series of samples appeared uniform. The most prominent electronic difference was the presence of a distinct band of near-interface defect states in the more non-uniform set of samples. The device performance did not appear to be limited by defects in the bulk CGS film until the defect density was larger than 2×1016 cm-3. Instead, interface recombination appears to be a significant factor limiting Voc in both sets of samples.

Charge transport through localized states in sputtered amorphous silicon suboxides

2001 ◽  
Vol 666 ◽  
Author(s):  
J.J. van Hapert ◽  
N. Tomozeiu ◽  
E.E. van Faassen ◽  
A.M. Vredenberg ◽  
F.H.P.M. Habraken
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Rf Magnetron Sputtering ◽  
Quantitative Information ◽  
Thin Layers ◽  
Localized States ◽  
Variable Range Hopping ◽  
Defect States ◽  
Variable Range ◽  
Spin Resonance

ABSTRACTUsing an RF magnetron sputtering technique, thin layers (∼500 nm) of amorphous silicon suboxides (a-SiOx) were deposited, with oxygen/silicon ratios x ranging from 0 to 1.8. These layers contain a large density (1020−1021 cm−3) of, mostly silicon dangling bond, defect states. The level of conduction decreases several orders of magnitude with increasing x. The temperature dependence of the DC conductivity showed that the variable range hopping conduction mechanism is dominant for all x, over the temperature range 30- 330 K. In this mechanism the extent of localization and density of states around the Fermi level determine the conductance. We conclude that the decrease in conductance with increasing oxygen content must, for a large part, be due to a variation in the localization, since Electron Spin Resonance (ESR) measurements showed no decrease in defect density with increasing x. We performed DC conduction measurements at both low and high electric field strengths, showing phenomena, which are consistently desribed within the variable range hopping (VRH) model. These measurements allow the extraction of quantitative information, concerning both the localization and the density of the states involved in the hopping process.

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.

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