Spin Relaxation Spectroscopy of the D-Center in Hydrogenated Amorphous Silicon

1989 ◽  
Vol 149 ◽  
Author(s):  
Sufi Zafar ◽  
E. A. Schiff
Keyword(s):  
Amorphous Silicon ◽  
Spin Relaxation ◽  
Hydrogenated Amorphous Silicon ◽  
Relaxation Processes ◽  
Substantial Variation ◽  
Paramagnetic Resonance ◽  
Electron Spin Relaxation ◽  
Order Of Magnitude ◽  
Hydrogenated Amorphous ◽  
Electron Paramagnetic

ABSTRACTMeasurements of the dependence of the D-center electron paramagnetic resonance absorption signal upon the incident microwave power are reported in undoped hydrogenated amorphous silicon (a-Si:H) for specimens prepared at differing deposition temperatures and also as the state of a given specimen was varied by illumination and subsequent annealing. These measurements are sensitive to electron spin relaxation processes of the D-center. Substantial variation in spin-relaxation behavior was found, corresponding to approximately one order of magnitude in the spin relaxation rate; no significant variations in absorption lineshape were observed. A model for these spin relaxation observations invoking two differing local microstructures near the D-center is proposed. The model indicates that illumination increases the density of defects in one microstructure but can irreversibly diminish the density in a second.

Structural Equilibration in Pure and Hydrogenated Amorphous Silicon

1993 ◽  
Vol 297 ◽  
Author(s):  
Gerhard Müller ◽  
Gerhard KrÖtz
Keyword(s):  
Amorphous Silicon ◽  
Degrees Of Freedom ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Electronic System ◽  
Relaxation Processes ◽  
Electrochemical Processes ◽  
Local Bonding ◽  
Defect Sites ◽  
Hydrogenated Amorphous

Chemically pure (a-Si) and hydrogenated amorphous silicon (a-Si:H) are metasta- ble materials which are thermodynamically unstable with respect to crystalline silicon (c-Si). In both materials, however, partial thermal equilibria can be established between certain structural, configurational and electronic degrees of freedom. The present paper discusses experiments on both amorphous (a-) materials showing that two kinds of structural change can take place within random Si networks: structural relaxation and configurational equilibration. The first process can be observed in both materials indicating that it is supported by intrinsic degrees of freedom of the random Si networks. During these changes partial thermal equilibria between distorted and broken bonds are established via irreversible and relatively long-range relaxation processes. The second kind of change can only be observed in a-Si:H, indicating that it is H-related. The H-related degrees of freedom support reversible valence alternation reactions in which the local bonding configuration of the dopant and defect sites is changed and in which their charge states are altered. These latter interactions establish a strong coupling between the electronic system and the configurational degrees of freedom of the random Si networks. Formally, these latter changes bear strong similarity to the electrochemical processes that take place in liquid electrolytes.

Anomalous Diffusion of Hydrogen and the Dependence of the Diffusion Constants on Hydrogen Content in Hydrogenated Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
R. Shinar ◽  
H. Jia ◽  
X.-L. Wu ◽  
J. Shinar
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Diffusion Constant ◽  
Relaxation Processes ◽  
Diffusion Constants ◽  
Amorphous Network ◽  
Sputter Deposited ◽  
Hydrogenated Amorphous ◽  
Deposited Film ◽  
Diffusion Of Hydrogen

ABSTRACTThe diffusion constant of hydrogen DH(t) in hydrogenated amorphous silicon (a-Si:H) is strongly dependent on the Si-bonded H content CH of the films. It increases by over four orders of magnitude for CH ranging from 1 to 19 at. %. In an rf sputter-deposited film of CH ∼5 at. % it increases with time at 300 ≤ T ≤ 362°C. The dispersion parameter α in DH(t) = D∞ (ωt)-αis thus negative. This observation and the increase of α with T above a sample-dependent temperature Tτ are discussed in relation to low temperature structural relaxation processes in the amorphous network.

Stability of hydrogenated amorphous silicon prepared by reactive evaporation

1991 ◽  
Vol 69 (6) ◽  
pp. 679-683
Author(s):  
D. C. Craigen ◽  
R. D. Audas ◽  
D. E. Brodie
Keyword(s):  
Activation Energy ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Time Curve ◽  
Switching Model ◽  
Order Of Magnitude ◽  
Reactive Gases ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous

Hydrogenated amorphous silicon (a-Si:H) was prepared by evaporating Si in a controlled ambient of reactive gases. Contamination of the samples by exposure to air affects both the dark conductivity and the photoconductivity. Some of the contamination effects can be removed by annealing, but some changes are not reversible. The irreversible changes are mainly due to the chemisorption of oxygen obtained from water vapour when the samples are stored in air. The Staebler–Wronski effect is observed in all samples whose photoconductivity is at least an order of magnitude higher than the dark conductivity. The photoconductivity versus time curve displays at t−1/3 dependence, typical of the Staebler–Wronski effect, but the degradation is much slower than that reported for glow discharge a-Si:H. The activation energy for the effect is 0.12 eV, which is larger than the 0.04 eV expected for the bond-switching model.

Effects of Fluorine Implantation into Hydrogenated Amorphous Silicon

1991 ◽  
Vol 235 ◽  
Author(s):  
S. P. Wong ◽  
Shaoqi Peng ◽  
Ning Ke ◽  
Jingxi Liu
Keyword(s):  
Amorphous Silicon ◽  
Spin Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Fluorine Concentration ◽  
Electrical Measurements ◽  
Large Shift ◽  
Before And After ◽  
Order Of Magnitude ◽  
Hydrogenated Amorphous

ABSTRACTMultiple-energy implantation of fluorine into rf glow discharge deposited hydrogenated amorphous silicon (a-Si:H) thin films has been performed. It is found that the optical gap decreases with the implanted fluorine concentration CF from 1.56 eV for the unimplanted sample to 1.40 eV for the sample with CF of 3×1021 cm−3. Results of the Staebler-Wronski experiment show that the ratio between the electrical conductivity before and after illumination, as well as the ratio between the photo- and dark conductivity, decrease also with Cp. Electrical measurements show that there is significant decrease in the conductivity activation energy Ea with CF for samples annealed at or below the substrate temperature TS during deposition. But for samples annealed at temperatures higher than TS, Ea was found to change back to values close to that of the unimplanted sample. A large shift to higher energy for one peak in the photoluminescence spectra at 77K has been observed, from 1.34 eV of the unimplanted sample to around 1.6 eV for the implanted samples, though with almost one order of magnitude weakening in intensity. It is also observed that ESR splitting has been induced in the fluorine implanted samples. The g-factors of the two resonances are determined to be 2.003 and 2.006, respectively. For the g=2.006 resonance, the spin density increases markedly after implantation but is essentially independent on CF before annealing and effectively reduced or eliminated after annealing. For the g=2.003 resonance, the spin density increases rapidly with CFp especially in the range from CF = 1×1020 to 1×1021 cm−3 before annealing and reduces only slightly after annealing.

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