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.

scholarly journals Material Parameters in a Thick Hydrogenated Amorphous Silicon Detector and their Effect on Signal Collection

1989 ◽  
Vol 149 ◽  
Author(s):  
S. Qureshi ◽  
V. Perez-Mendez ◽  
S. N. Kaplan ◽  
I. Fujieda ◽  
G. Cho
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Silicon Detector ◽  
Dangling Bond ◽  
Material Parameters ◽  
Bond Density ◽  
Transient Photoconductivity ◽  
Signal Collection ◽  
Hydrogenated Amorphous

ABSTRACTTransient photoconductivity and ESR measurements were done to relate the ionized dangling bond density and the spin density of thick hydrogenated amorphous silicon (a-Si:H) detectors. We found that only a fraction (∼30–35%) of the total defect density as measured by ESR is ionized when the detector is biased into deep depletion. The measurements on annealed samples also show that this fraction is about 0.3. An explanation based on the shift of the Fermi energy is given. The measurements show that the time dependence of relaxation is a stretched exponential.

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.

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.

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.

Effects of Intermittent Deposition on the Defect Density in a-Si:H

1994 ◽  
Vol 336 ◽  
Author(s):  
Toshihiro Kamei ◽  
Nobuhiro Hata ◽  
Akihisa Matsuda
Keyword(s):  
Waiting Time ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Hydrogen Desorption ◽  
Growth Surface ◽  
Dangling Bond ◽  
Monolayer Growth ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures ◽  
Mechanical Shutter

ABSTRACTEffects of intermittent deposition on the defect density in hydrogenated Amorphous silicon (a-Si:H) are investigated at various substrate temperatures by using a mechanical shutter, while maintaining the discharge continuously. The intermittent deposition experiments, where monolayer growth and intermission (waiting time) are repeated in cycles, enable us to study surface dangling bond (DB) recombination and thermal hydrogen desorption separately from other reactions on the growth surface. The defect density in films prepared at lower substrate temperatures decreases with the waiting time, while that deposited at higher substrate temperatures increases with the waiting time.

The Concentration of (SiH2)n Sites in Low and High Defect Density a-Si:H

2006 ◽  
Vol 910 ◽  
Author(s):  
David C. Bobela ◽  
T. Su ◽  
P. C. Taylor ◽  
A. Madan ◽  
G. Ganguly
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Hydrogen Content ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Proton Nuclear Magnetic Resonance ◽  
Dangling Bond ◽  
High Defect Density ◽  
Quality Material ◽  
Hydrogenated Amorphous

AbstractThe concentration of polysilane chains (SiH2)n, where n≥1, is estimated for higher quality hydrogenated amorphous silicon (a-Si:H) by pulsed proton nuclear magnetic resonance techniques (1H NMR). Our measurements indicate the minimum hydrogen content of approximately 10% of the total hydrogen is in the (SiH2)n configuration. Similar measurements in a high defect density sample (1017 silicon dangling bond defects cm-3) show that (SiH2)n sites account for ~ 15% of the total hydrogen. While the (SiH2)n infrared absorption (IR) modes are observed in the highly defective sample, no such modes are seen in the higher quality material. The results indicate that a significant amount of the total hydrogen content exists as (SiH2)n regardless of film quality.

Growth Processes of Hydrogenated Amorphous Silicon

2000 ◽  
Vol 609 ◽  
Author(s):  
John Robertson
Keyword(s):  
Low Temperature ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Surface Layers ◽  
Bond Density ◽  
Hydrogen Elimination ◽  
Type Process ◽  
Rate Limiting ◽  
Hydrogenated Amorphous ◽  
Pool Type

ABSTRACTThe surface and subsurface processes occurring during the growth of a-Si:H are analysed to understand why dangling bond defects and weak Si-Si bonds form. We argue that hydrogen elimination to form the Si-Si network is the rate limiting process at low temperature, and this leads to the creation of weak Si-Si bonds. Dangling bonds form subsequently from weak bonds by a defect pool type process. Plasma processes, such as ion bombardment, which dehydrogenate the surface layers, can reduce the weak bond density.

scholarly journals Impurity-Defect Complexes in Hydrogenated Amorphous Silicon

1990 ◽  
Vol 209 ◽  
Author(s):  
Lin H. Yang ◽  
C. Y. Fong ◽  
Carol S. Nichols
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Defect Complexes ◽  
Amorphous Network ◽  
Pseudopotential Calculations ◽  
Impurity Defect ◽  
Supercell Model ◽  
Hydrogenated Amorphous

ABSTRACTThe two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H) - a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping - have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using firstprinciples self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfoldcoordinated phosphorus and boron at the second neighbor position to a dangling bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H.

Sign in / Sign up

Export Citation Format

Share Document