Defect Relaxation in Disordered Materials: Stretched Exponentials, Meyer-Neldel Rule, and Staebler-Wronski Effect

1989 ◽  
Vol 149 ◽  
Author(s):  
Richard S. Crandall
Keyword(s):  
Exponential Distribution ◽  
Charge Trapping ◽  
Bond Breaking ◽  
Disordered Materials ◽  
Activation Barriers ◽  
Metastable Effects ◽  
Staebler Wronski Effect ◽  
Stretched Exponentials ◽  
Hydrogenated Amorphous ◽  
Defect Relaxation

ABSTRACTUsing an exponential distribution of activation barriers, annealing data for metastable effects in hydrogenated amorphous silicon, a-Si:H, are quantitatively explained. This includes the stretched exponential time dependence of annealing and a Meyer-Neldel rule for the annealing time constant. An exponential distribution of annealing energies arises because defects are frozen in during growth at high temperature. Mechanisms that lead to an exponential distribution of annealing energies are weak bond-breaking and charge trapping.

New Results on Enhanced Deuterium Diffusion Under Illumination in Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
Howard M. Branz ◽  
Sally E. Asher ◽  
Brent P. Nelson
Keyword(s):  
Amorphous Silicon ◽  
Room Temperature ◽  
Red Light ◽  
Hydrogenated Amorphous Silicon ◽  
Dissimilar Materials ◽  
Bond Breaking ◽  
Light Enhancement ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous ◽  
Bulk Effect

ABSTRACTWe measure the light-enhancement of D diffusion in hydrogenated amorphous silicon and determine that the mechanism for the effect is an increase of the rate of Si-D bond breaking under illumination. We exclude light-induced heating of the sample and light-induced excitation of D between dissimilar materials as sources of the light-enhancement. It is a bulk effect, most likely caused by excess carriers. We are able to observe the light-induced effect with 380 mW-cm-2 of red light, an intensity only slightly larger than the intensity normally used to induce the Staebler-Wronski effect. At room temperature, the effect is unobservable and we derive an upper bound of 2 × 10-8 photon-1 for the efficiency of light-induced Si-D bond breaking. Implications for the Staebler-Wronski effect are discussed.

Improved Light Soaking Stability of R.F. Sputter Deposited Amorphous Silicon

1991 ◽  
Vol 219 ◽  
Author(s):  
A. Wynveen ◽  
J. Fan ◽  
J. Kakalios ◽  
J. Shinar
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Initial Defect ◽  
Optical Gap ◽  
Sputter Deposited ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous

ABSTRACTStudies of r.f. sputter deposited hydrogenated amorphous silicon (a-Si:H) find that the light induced decrease in the dark conductivity and photoconductivity (the Staebler-Wronski effect) is reduced when the r.f. power used during deposition is increased. The slower Staebler-Wronski effect is not due to an increase in the initial defect density in the high r.f. power samples, but may result from either the lower hydrogen content or the smaller optical gap found in these films.

The Role of Deep Defect Relaxation Dynamics in Optical Processes in Hydrogenated Amorphous Silicon

1995 ◽  
Vol 377 ◽  
Author(s):  
Fan Zhong ◽  
J. David Cohen
Keyword(s):  
Relaxation Dynamics ◽  
Energy Position ◽  
Defect Band ◽  
Transient Photoconductivity ◽  
Photoconductivity Decay ◽  
Long Time ◽  
Intimate Relation ◽  
Hydrogenated Amorphous ◽  
Defect Relaxation

ABSTRACTWe report results of a transient modulated photocurrent technique which allows us to observe the time evolution of the D0 sub-band under the application of optical bias light and after turning off this bias light Our measurements show that the D0 band shifts monotonically to shallower thermal energies after the bias light is applied, with roughly 10 seconds to saturation at 300K and to deeper thermal energies after removing the bias light, with a decay time of over 1000 seconds. We have also found there exists an intimate relation between the motion of the D0 band and that of the quasi Fermi level as deduced from the transient photoconductivity and therefore, in particular, to the long time photoconductivity decay. This relation is exactly reproduced by the assumption of a D0 band whose energy position evolves in time, together with a recombination process dominated by changes in the charge state of a deeper defect band under light bias.

Search for Explaining the Staebler-Wronski Effect

1997 ◽  
Vol 467 ◽  
Author(s):  
H. Fritzsche ◽  
Tucson Az
Keyword(s):  
Spatial Correlation ◽  
Long Range ◽  
Photon Energy ◽  
Structural Changes ◽  
Hydrogen Diffusion ◽  
Critical Value ◽  
Bond Breaking ◽  
Dangling Bond ◽  
High Fields ◽  
Staebler Wronski Effect

ABSTRACTFor twenty years we searched to understand the Staebler-Wronski effect (SWE). New results continue to emerge which invalidate prior interpretations. Recent evidence shows that the SWE is not associated with impurities. Long-range hydrogen diffusion is ruled out because the SWE occurs with comparable efficiency between 400K and the lowest temperatures. Nonradiative geminate recombinations might be important since high fields reduce the SWE significantly. It disappears when the bandgap or the photon energy falls below a critical value. The creation of a metastable density of dangling bond defects has been considered to be its sole manifestation. However, there is mounting evidence for light-induced structural changes which extend throughout the material. The weak bond breaking model emerges as the only viable explanation of the SWE if the expected spatial correlation between defects and hydrogen is destroyed by subsequent recombination events. The SWE is reduced by a favorable microstructure and low hydrogen content. It is suggested that defect pairs have larger recombination coefficients than isolated defects.

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