Mechanisms for Metastability in Hydrogenated Amorphous Silicon

2000 ◽  
Vol 609 ◽  
Author(s):  
R. Biswas ◽  
Y.-P. Li ◽  
B.C. Pan
Keyword(s):  
Amorphous Silicon ◽  
Structural Changes ◽  
Defect Formation ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
New Model ◽  
Gap States ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTWe propose metastabilities in amorphous silicon fall into two classes. One class is the local changes of structure affecting a macroscopic fraction of sites. The other class is the metastable generation of dangling bonds with mid-gap states. The local metastability is explained by a new metastable state formed when H is flipped to the backside of the Si-H bond at monohydride sites. The dipole moment of this H-flip defect is larger and increases the infrared absorption. This H-flip defect accounts for large structural changes observed on light soaking including larger absorption and volume dilation. We propose a new model for the generation of metastable dangling bonds. The new ‘silicon network rebonding model’ involves breaking of weak silicon bonds and formation of isolated dangling bonds, through rebonding of the silicon network. Hydrogen motion is not involved in metastable defect formation. Defect formation proceeds by breaking weak silicon bonds and formation of dangling bond-floating bond pairs. The floating bonds migrate through the network and annihilate, producing isolated dangling bonds. This new model provides a new platform for understanding the atomistic origins of lightinduced degradation.

Dangling-Bond Relaxation and Metastability in P-Type Hydrogenated Amorphous Silicon

1995 ◽  
Vol 377 ◽  
Author(s):  
Richard S. Crandall ◽  
Martin W. Carlen ◽  
Klaus Lips ◽  
Yueqin Xu
Keyword(s):  
Elevated Temperature ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Type A ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Hole Trapping ◽  
P Type ◽  
Hydrogenated Amorphous

ABSTRACTWe discuss the subtle effects involved in observing slow dangling bond relaxation by studying capacitance transients in p-type hydrogenated amorphous silicon (a-Si:H). The data suggest that neutral dangling bonds are reversibly converted into metastable positive charged dangling bonds by hole trapping. These metastable positive dangling bonds reconvert to neutral dangling bonds upon annealing at elevated temperature. The annealing kinetics for this process are the same as those observed for annealing of quenched in conductivity changes in p-type a-Si:H.

Defect Thermodynamics, Inhomogeneity, and the Density of Gap States in Hydrogenated Amorphous Silicon

1990 ◽  
Vol 192 ◽  
Author(s):  
Howard M. Branz ◽  
Marvin Silver
Keyword(s):  
Amorphous Silicon ◽  
Defect Formation ◽  
Numerical Solutions ◽  
Correlation Energy ◽  
Hydrogenated Amorphous Silicon ◽  
Level Energy ◽  
Dangling Bond ◽  
Potential Fluctuations ◽  
Material Inhomogeneity ◽  
Hydrogenated Amorphous

ABSTRACTA new hydrogenated amorphous silicon (a-Si:H) density of states (d.O.s.) in+cluding the transition levels of both neutral (T3o) and charged (T3+ and T3−) dangling-bond defects is proposed. We derive closed-form and numerical solutions for the d.o.s. from a thermodynamic equilibrium theory of defect concentrations in which material inhomogeneity is assumed to give rise to ∼1020 cm−3 of electrostatic potential fluctuations. The connection between thermodynamic transition level energy and defect formation energy implicit in this and other “defect pool” models is included explicitly in the calculation. We calculate the d.o.s. for a range of parameters and for different values of Fermi energy. We apply the calculated d.o.s. to explain and unify various experimental results in a-Si:H. In particular, we reconcile recent depletion-width-modulated ESR data with the near-perfect Curie law T-dependence of the dangling-bond spin density observed by several groups. It is seen +that the depletion results in roughly equal numbers of T3−T3–>° and T3°–>T3+ transitions despite the positive value of effective correlation energy. We also discuss possible sources of the short-to-medium range potential fluctuations in amorphous silicon.

Bonded Hydrogen Atom Participation in Metastable Defect Formation in Hydrogenated Amorphous Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
G. Lucovsky ◽  
H. Yang
Keyword(s):  
Hydrogen Atom ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Amorphous Silicon ◽  
Defect Formation ◽  
Hydrogenated Amorphous Silicon ◽  
Reaction Pathways ◽  
Reaction Barriers ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTThis paper proposes intrinsic reaction pathways for generation of metastable defects in hydrogenated undoped or intrinsic amorphous silicon (i-a-Si:H). Since these pathways involve only silicon (Si) and hydrogen (H) atoms, this approach is valid for device grade materials in which concentrations of oxygen (0) atoms, and nitrogen-hydrogen (N-H) groups are present at concentrations below about 1019 cm−3. Ab initio calculations demonstrate that the proposed generation pathway reactions are exothermic with relatively small reaction barriers (< 0.4 eV).

Correlation of Film Quality and Hydrogen NMR Resonance Shifts in a-Si:D,H; a-Ge:D,H; and a-SiGe:D,H

1995 ◽  
Vol 377 ◽  
Author(s):  
R. E. Norberg ◽  
Y. W. Kim ◽  
P. H. Chan ◽  
J. R. Bodart ◽  
M. J. Kernan ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Systematic Study ◽  
Hydrogenated Amorphous Silicon ◽  
Spectral Features ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Hydrogen Molecules ◽  
Hydrogenated Amorphous ◽  
Significant Resonance ◽  
Deposition Conditions

ABSTRACTA systematic study of both proton and deuteron NMR in hydrogenated amorphous silicon films has revealed significant resonance shifts among various resolved components. The shifts include both paramagnetic and diamagnetic displacements of resolved spectral features from trapped molecular hydrogens. The shifts depend on film quality and deposition conditions. Some of the shifts vary as 1/T and reflect Curie susceptibilities characteristic of local regions of differing dangling bond densities. Spectra from relatively immobile hydrogen molecules trapped in nanovoids are shifted diamagnetically and broadened as temperature decreases. Hydrogens tightly bound to Si do not show similar changes and thus are more remote from dangling bonds and other magnetic defects. Similar spectrally-resol ved shifts have been observed in a-Ge and a-SiGe films and are correlated with film photovoltaic quality as measured by mobility-lifetime products.

Capacitance Studies of Metastable Defect Creation in Hydrogenated Amorphous Silicon

1986 ◽  
Vol 70 ◽  
Author(s):  
J. D. Cohen ◽  
K. Mahavadi ◽  
K. Zellama ◽  
J. P. Harbison ◽  
A. E. Delahoy
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Microscopic Models ◽  
Deep State ◽  
Absorption Studies ◽  
Defect Creation ◽  
Metastable Effects ◽  
Gap States ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTWe have studied the light induced instability problem in hydrogenated amorphous silicon using junction capacitance techniques. These techniques are used to examine specific changes in the density of gap states, and occupation of gap states, for undoped a-Si:H samples after light saturation and for a series of partial anneal “states” which culminate in the original dark annealed state (state A). We find that the observed changes in the metastable occupied and unoccupied defects contradict the Si-Si bond breaking model and indicate at least two defect creation processes. In several samples we also find clear evidence that the metastable defect distribution near midgap has a slightly different energy distribution than the stable deep state (dangling bond) distribution. At the same time, these results seem to be qualitatively consistent with many aspects of recent ESR and optical absorption studies of metastable defect creation. We discuss these findings in terms of alternative possible microscopic models for metastable effects in a-Si:H.

Microscopic Model for Creation And Removal of Metastable Dangling Bonds in a-Si:H

2002 ◽  
Vol 715 ◽  
Author(s):  
M.J. Powell ◽  
S.C. Deane ◽  
R.B. Wehrspohn
Keyword(s):  
Amorphous Silicon ◽  
Mechanical Stress ◽  
Hydrogenated Amorphous Silicon ◽  
Microscopic Model ◽  
Stress Dependence ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Defect Creation ◽  
Hydrogenated Amorphous

AbstractWe present a new microscopic model for metastable Si dangling bond defect creation in hydrogenated amorphous silicon, which is applicable to both light-induced and carrier-induced defect creation. The key feature of our model is that hydrogen is always in the tedrahedral-like site, which is strongly bound in amorphous silicon, and never in the bond-centered site. Breaking of Si-Si bonds and successive stabilisation by bond-switching of nearby hydrogen from doubly hydrogenated Si-Si bonds (SiHHSi) results in two hydrogen-stabilised dangling bonds (SiHD). Since hydrogen is in the Td site in all configurations, this defect creation reaction is consistent with ESR, NMR, hydrogenation experiments and the mechanical stress dependence of defect creation.

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