Electron Spin Resonance and Electronic Conductivity in Moderately Doped n-type Microcrystalline Silicon as a Probe for the Density of Gap States

2002 ◽  
Vol 715 ◽  
Author(s):  
T. Dylla ◽  
R. Carius ◽  
F. Finger
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Structural Changes ◽  
Defect Density ◽  
Electronic Conductivity ◽  
Intrinsic Defect ◽  
Charge Carrier Density ◽  
Microcrystalline Silicon ◽  
Spin Resonance ◽  
Gap States

AbstractElectron spin resonance accompanied by conductivity measurements in n-type microcrystalline silicon with different doping concentrations and different structure compositions has been applied for the study of the density of gap states and the influence of these states on charge carrier density. We studied doping concentrations close to the defect density where the doping induced Fermi level (EF) shift is determined by compensation of gap states. We found a correlation between the EF shift, the intrinsic defect density and structural changes.

Study of the Density of Bulk Gap States in Undoped a-Si:H by Depletion Width Modulation Electron Spin Resonance

1989 ◽  
Vol 149 ◽  
Author(s):  
J. M. Essick ◽  
J. D. Cohen
Keyword(s):  
Electron Spin Resonance ◽  
Schottky Barrier ◽  
Electron Spin ◽  
Correlation Energy ◽  
Thick Layer ◽  
Resonance Spectroscopy ◽  
Model Calculations ◽  
Depletion Width ◽  
Spin Resonance ◽  
Gap States

ABSTRACTThe density of gap states in the bulk of intrinsic a-SiH has been probed using depletion width modulation electron spin resonance spectroscopy (DWM ESR) as well as complementary capacitance techniques. Our sample consists of a 2.85 micron thick layer of undoped a-Si:H sandwiched between a large area Pd Schottky barrier contact and a p+ c-Si substrate, allowing charge-counting capacitance and spin-counting ESR measurements to be performed on the same sample. DWM ESR measures the spin change that occurs when electrons are removed from gap states by increasing reverse bias on a Schottky barrier. The phase of the signal indicates whether unpaired spins are created or destroyed with increasing bias, thus revealing the defect charge state at the Fermi level The DWM ESR signal from our sample indicates that removing electrons from gap states leads to a reduction of the spin signal. This is qualitatively consistent with a band of Do states near EFo. However, for all metastable states and at all temperatures studied, the magnitude of the DWM ESR signal account for only about 14% of the responding charge as determined by junction capacitance. This would occur only if the majority of the filled bulk gap states were doubly occupied with a small correlation energy Ueff. In that case the majority of transitions caused by depletion width modulation would be D−/D+ which would produce no spin change. Model calculations show that the small observed Do/D+ DWM ESR signal would indeed result from the occupation statistics for a near zero value of Ueff at the moderate temperatures of the experiment. Comparison with our data sets the overall limits If −20meV < Ueff < 50 meV. Implication for recent models of the density of states in intrinsic a-Si:H are discussed.

Spin Resonance Studies on free Electrons and Defects in Microcrystalline Silicon

1994 ◽  
Vol 358 ◽  
Author(s):  
C. Malten ◽  
F. Finger ◽  
P. Hapke ◽  
T. Kulessa ◽  
C. Walker ◽  
...  
Keyword(s):  
Electron Spin Resonance ◽  
Grain Boundaries ◽  
Amorphous Phase ◽  
Electron Spin ◽  
Degree Of Crystallinity ◽  
Microcrystalline Silicon ◽  
Free Electrons ◽  
Conduction Band Offset ◽  
Spin Resonance ◽  
Material Points

ABSTRACTThe effect of micro-doping, defect creation, and non-steady state occupation through optical transitions on the electron spin resonance signals found in undoped and weakly doped microcrystalline silicon with a high degree of crystallinity is investigated. The experimental results are in agreement with the assignment of the resonance at g=1.9983 to conduction electrons in the crystalline grains and the resonanccs around g=2.0052 to dangling bonds in the remaining amorphous phase and at the grain boundaries. The simultaneous presence of both resonances can result from a large conduction band offset between crystalline grains and grain boundaries or the amorphous phase. The presence of conduction electron spin resonance in compensated and even p-type material points also to potential fluctuations. Free electrons in interconnected crystalline grains are in agreement with the weakly activated transport found in µc-Si:H at low temperatures.

Defect and Tail States in Microcrystalline Silicon investigated by pulsed ESR

2000 ◽  
Vol 609 ◽  
Author(s):  
P. Kanschat ◽  
H. Mell ◽  
K. Lips ◽  
W. Fuhs
Keyword(s):  
Electron Spin Resonance ◽  
Detailed Analysis ◽  
Electron Spin ◽  
Qualitative Model ◽  
Dangling Bond ◽  
Microcrystalline Silicon ◽  
Band Tail ◽  
Spin Resonance ◽  
Donor States ◽  
Broad Structure

ABSTRACTWe report on a detailed analysis of paramagnetic states in a doping series of microcrystalline silicon, μc-Si:H, by pulsed electron spin resonance. We identify two dangling bond like structures at g = 2.0052 (db1) and g = 2.0043 (db2). Whereas db1 is evenly distributed in the gap, the db2 state is found to be localized in the lower part of the gap. The CE resonance at g ≈ 1.998 is assigned to electrons in conduction band tail states. In p-doped samples, we observe a broad structure CH at g ≈ 2.08 which we identify with holes trapped in valence band tail states. It is shown that the CH state behaves very similar on illumination as the CE resonance. In n-type samples a pair of hyperfine split lines (A ≈ 11 mT) is found which apparently does not originate from 31P-donor states. On the basis of our results we propose a qualitative model for paramagnetic states in μc-Si:H.

Effect of C Impurities in a-Si:H as Measured by Drive-Level Capacitance, Photo Current, and Electron Spin Resonance

1993 ◽  
Vol 297 ◽  
Author(s):  
J. Hautala ◽  
T. Unold ◽  
J.D. Cohen
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Defect Density ◽  
Drive Level ◽  
Level Data ◽  
Definite Effect ◽  
Wide Range ◽  
Spin Resonance ◽  
Defect Densities ◽  
Photo Current

The effect of C impurities in a-Si:H in levels of 0.4 to 2.6 at. % were studied over a wide range of metastable defect densities. Three complimentary experimental techniques [electron spin resonance (ESR), drive-level capacitance (DLC) and photo-current] were employed to track the material's defect density with light soaking and annealing, as well as Urbach energies, midgap absorption and mobility gaps energies as a function of the C content. Our results show C impurities have a definite effect on the initial and saturated defect densities, as well as the midgap absorption and Urbach energies at levels 1 at. % and above. The results indicate that C acts mainly as a center for increased disorder in the material which results in an increase in the bandtail widths, and consequently an increase in intrinsic defects. Comparison to the ESR and drive-level data show an excellent agreement between these two techniques in determining the bulk defect densities in a-Si:H.

TRANSITION METALS EFFECT ON THE STRUCTURE OF PYRAZINAMIDE COMPLEXES

2004 ◽  
Vol 18 (01) ◽  
pp. 63-70 ◽  
Author(s):  
V. SIMON ◽  
T. JURCA ◽  
S. SIMON
Keyword(s):  
Phase Transition ◽  
Electron Spin Resonance ◽  
Transition Metal Complexes ◽  
Electron Spin ◽  
Crystalline Phase ◽  
Structural Changes ◽  
Thermal Transformations ◽  
First Line ◽  
Spin Resonance ◽  
Crystalline Phase Transition

Pyrazinamide (PZA) is among the first-line drugs for the treatment of tuberculosis, which seems to reappear as a frequent disease. In this study we investigate the structural changes induced in these samples as evidenced by thermal behaviour and electron spin resonance of new transition metal complexes of PZA. We is search for a correlation between structure and thermal transformations described as multi-step processes consisting in crystalline phase transition, decomposition, melting and thermo-oxidation.

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