Coupled Effects of Light and Temperature on Degradation of a-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Lisa E. Benatar ◽  
Michael Grimbergen ◽  
David Redfeeld ◽  
Richard H. Bube
Keyword(s):  
Steady State ◽  
Defect Formation ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Gradual Change ◽  
State Behavior ◽  
Excitation Rate ◽  
Barrier Heights ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTThe effects of excitation rate and temperature on the kinetics and steady-state behavior of metastable defect formation in hydrogenated amorphous silicon (a-Si:H) have been studied. The dependences on temperature of the lifetime, τ, and stretching parameter, β, from a stretched exponential description of the kinetics were measured for one sample. We do not see a linear dependence of β on temperature over die entire temperature range studied (270K–370K), and τ increases monotonically with decreasing temperature. Steady-state results show defect density to be dependent on bodi temperature and excitation rate over the ranges measured (from 395K to 470K and from 6 × 1020 to 2 × 1022 s-l cm-3). The gradual change in temperature dependence is explained by a distribution of barrier heights between the ground and metastable states.

The Effect of Post-Deuteration on Metastability in a-Si:H

1993 ◽  
Vol 297 ◽  
Author(s):  
N.H. Nickel ◽  
W.B. Jackson ◽  
C.C. Tsai
Keyword(s):  
Defect Formation ◽  
Chemical Potential ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Deuterium Plasma ◽  
Bond Density ◽  
Intense Light ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

Hydrogenated amorphous silicon films were deuterated through a sequence of 1h exposures to a remote deuterium plasma at 350°C. The concentration profiles of hydrogen and deuterium were determined by SIMS at various times during the exposure sequence. The defect density in state A, after deuteration and after illumination with white light were determined using CPM measurements following each 1h exposure sequence. We find that post-deuteration does not alter the defect density in state A, change the Urbach edge, nor significantly alter metastable defect formation. Intense light soaking increases the defect density by about 5 × 10l6cm−3 independent of the total H + D concentration. These results suggest that D always enters the sample in pairs pinning the hydrogen chemical potential which supports the idea of a negative U system for hydrogen and deuterium. Despite an increase of Si-H bonds by as much as 3 × 1021cm−3, the annealed dangling bond density and the weak Si-Si bond density did not change.This suggests that the density of weak Si-Si bonds as well as the dangling bond density is determined by equilibration with strong Si-Si bonds through the interchange of H. The implications of these results for H bonding will be discussed.

Light-Induced Metastable Defects or Light-Induced Metastable H Atoms in a-Si:H Films?

1997 ◽  
Vol 467 ◽  
Author(s):  
C. Godet
Keyword(s):  
Experimental Data ◽  
Characteristic Time ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Exponential Time ◽  
Mobile Species ◽  
Hydrogenated Amorphous ◽  
Two Parameter ◽  
Metastable Defect ◽  
Trapping Sites

ABSTRACTIn hydrogenated amorphous silicon (a-Si:H) films, the increase of the metastable defect density under high-intensity illumination is usually described by an empirical two-parameter stretched-exponential time dependence (characteristic time τSE and dispersion parameter β). In this study, a clearly different (one-parameter) analytic function is obtained from a microscopic model based on the formation of metastable H (MSH) atoms in a-Si:H films. Assuming that MSH atoms are the only mobile species, only three chemical reactions are significant : MSH are produced from doubly hydrogenated (SiH HSi) configurations and trapped either at broken bonds or Si-H bonds, corresponding respectively to light-induced annealing (LIA) and light-induced creation (LIC) of defects. Competition between trapping sites results in a saturation of N(t) at a steady-state value Nss. A one-parameter fit of this analytical function to experimental data is generally good, indicating that the use of a statistical distribution of trap energies is not necessary.

Dependence of Steady-State Defect Density in Hydrogenated Amorphous Silicon on Carrier Generation Rate Studied Over a Wide Range

1993 ◽  
Vol 297 ◽  
Author(s):  
Nobuhiro Hata ◽  
Gautam Ganguly ◽  
Akihisa Matsuda
Keyword(s):  
Steady State ◽  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Continuous Light ◽  
Effective Rate ◽  
Defect States ◽  
Carrier Generation ◽  
Wide Range ◽  
Hydrogenated Amorphous

Measurements of the steady-state defect density (Nst) in hydrogenated amorphous silicon under illumination of pulse-laser light, as well as of continuous light, were carried out; and the dependence of Nst on the effective rate of carrier generation (G) is presented. The values of G ranged from 8 x 1021 to 2.4 × 1023 cm-3 s-1, while the illumination temperature was kept at 30 °C or at 105 °C. The results showed trends of Nst increasing with G similarly to the trends in the literature, but covered a higher and wider G range, and fitted a defect model which assumes a limited number of possible defect states.

Pulsed-Light-Induced Metastable Defect Creation in Hydrogenated Amorphous Silicon

1995 ◽  
Vol 377 ◽  
Author(s):  
Jong-Hwan Yoon ◽  
H. L. Kim
Keyword(s):  
Time Dependence ◽  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Pulsed Light ◽  
Illumination Time ◽  
Defect Creation ◽  
Annealing Rate ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

ABSTRACTWe report the results of a study of metastable defect creation by pulsed light soaking in undoped hydrogenated amorphous silicon (a-Si:H). An illumination time dependence of the defect density, a saturated defect density, and light-induced annealing under pulsed laser light have been studied. Measurements show approximately a t1/2 time-dependence of the defect creation, which is independent of light intensity. It is observed that the saturation value of the defect density is about one order of magnitude higher than by cw illumination in device quality films. It has been suggested that these results would be due to the difference in the light-induced defect annealing rate between cw and pulsed lights, in which it is found that the light-induced annealing rate by pulsed light is lower than by cw light.

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).

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.

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