The Role of Charged Defects In Current Transport Through Hydrogenated Amorphous Silicon Alloys

1998 ◽  
Vol 507 ◽  
Author(s):  
S.P. Lau ◽  
J.M. Shannon ◽  
B.J. Sealy ◽  
J.M. Marshall
Keyword(s):  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Defect Density ◽  
Current Transport ◽  
Dangling Bond ◽  
Silicon Alloys ◽  
Metal Structures ◽  
Bond State ◽  
Donor States ◽  
Charged Defects

ABSTRACTCurrent transport in metal-semiconductor-metal structures based on amorphous silicon alloys has been studied in relation to the density of dangling bond state defects. The density of defects was changed by varying alloy composition or by current stressing. We show that the change of current-voltage characteristics and activation energy with defect density and the onset of Poole-Frenkel conduction with composition require charged defects. It is found that there are more charged defects in amorphous silicon nitride (a-Si1−xNx:H) than in amorphous silicon carbide (a-Si1−xCx:H). In addition, an excess of negatively charged dangling bond defects compared to positively charged dangling bond defects is observed in a-Si1−xNx:H films. This is attributed to the presence of N4+ act as the donor states in silicon nitride. We find that the density of charged dangling bond defects can be higher than 1019cm−3.

Metastable Defects in Tritiated Amorphous Silicon

2007 ◽  
Vol 989 ◽  
Author(s):  
Tong Ju ◽  
Janica Whitaker ◽  
Stefan Zukotynski ◽  
Nazir Kherani ◽  
P. Craig Taylor ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Liquid Nitrogen ◽  
Beta Decay ◽  
Defect Density ◽  
Average Energy ◽  
Liquid Nitrogen Temperature ◽  
Beta Particle ◽  
Dangling Bond ◽  
Staebler Wronski Effect ◽  
Induced Defects

AbstractThe appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to 3He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half âlife of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 1016 to 1017 /cm3 , which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3x1019/cm3 after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2x1020/cm3). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200°C, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150°C, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.

A Critical Test of Defect Creation Models in Hydrogenated Amorphous Silicon Alloys

2000 ◽  
Vol 609 ◽  
Author(s):  
Kimon C. Palinginis ◽  
Jeffrey C. Yang ◽  
S. Guha ◽  
J. David Cohen
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Dangling Bonds ◽  
Silicon Alloys ◽  
Illumination Time ◽  
Deep Defect ◽  
Photocurrent Spectroscopy ◽  
Defect Creation ◽  
The Creation ◽  
Kinetics Of

ABSTRACTUsing the modulated photocurrent method we studied the deep defect creation and annealing kinetics of amorphous silicon-germanium alloys with Ge fractions below 10at.%. The modulated photocurrent spectroscopy clearly discloses the existence of two distinct bands of majority carrier traps in these alloys. The bands were identified as neutral Si dangling bonds and neutral Ge dangling bonds. Our studies show clearly that the Si and Ge defects directly compete with each other during annealing, implying a global reconfiguration mechanism. The creation kinetics reveal the usual t1/3 illumination time dependence for the total deep defect density. However, the individual densities of Si and Ge defects have different time dependencies. The details of the creation and annealing kinetics of Ge and Si defects are used to test predictions of certain defect creation models.

Structural identification of the silicon and nitrogen dangling‐bond centers in amorphous silicon nitride

1991 ◽  
Vol 70 (1) ◽  
pp. 346-354 ◽  
Author(s):  
William L. Warren ◽  
F. Christopher Rong ◽  
Edward H. Poindexter ◽  
Gary J. Gerardi ◽  
Jerzy Kanicki
Keyword(s):  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Structural Identification ◽  
Dangling Bond ◽  
Amorphous Silicon Nitride

Energy level of the nitrogen dangling bond in amorphous silicon nitride

1991 ◽  
Vol 59 (14) ◽  
pp. 1699-1701 ◽  
Author(s):  
W. L. Warren ◽  
J. Kanicki ◽  
J. Robertson ◽  
P. M. Lenahan
Keyword(s):  
Silicon Nitride ◽  
Energy Level ◽  
Amorphous Silicon ◽  
Dangling Bond ◽  
Amorphous Silicon Nitride

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.

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.

Equilibration in Amorphous Silicon Nitride Alloys

1995 ◽  
Vol 377 ◽  
Author(s):  
Bruce Dunnett ◽  
Christopher H. Cooper ◽  
Darren T. Murley ◽  
Roderick A. G. Gibson ◽  
David I. Jones ◽  
...  
Keyword(s):  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Growth Temperature ◽  
Vapour Deposition ◽  
Defect Density ◽  
Chemical Vapour ◽  
Amorphous Silicon Nitride ◽  
Photothermal Deflection Spectroscopy ◽  
Photothermal Deflection ◽  
Deposition Conditions

ABSTRACTSeveral series of amorphous silicon nitride thin films have been grown by plasma-enhanced chemical vapour deposition, where the ratio of ammonia and silane feed gases was held constant for each series while the deposition temperature was varied from 160 °C to 550 °C, and all other deposition conditions were held constant. Photothermal Deflection Spectroscopy measurements were used to determine the Urbach slope E0 and the defect density ND. It is found that ND is determined by E0 for most of these samples, suggesting that defect equilibration occurs in a-SiNx:H for x up to at least 0.6. The growth temperature at which the disorder is minimised increases to higher values with increasing x, which is explained in terms of a hydrogen-mediated bond equilibration reaction. Fourier Transform Infra Red spectroscopy measurements were performed to determine the changes in hydrogen bonding with growth temperature. The results suggest that a second bond equilibration reaction also occurs at the growing surface, but that equilibrium cannot be reached at higher temperatures because of hydrogen evolution from Si-H bonds.

Material Properties Controlling the Performance of Amorphous Silicon Thin Film Transistors

1984 ◽  
Vol 33 ◽  
Author(s):  
M. J. Powell
Keyword(s):  
Thin Film ◽  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Threshold Voltage ◽  
Material Properties ◽  
Thin Film Transistors ◽  
Gate Insulator ◽  
Dangling Bond ◽  
Silicon Thin Film

ABSTRACTAmorphous silicon thin film transistors have been fabricated with a number of different structures and materials. To date, the best performance is obtained with amorphous silicon - silicon nitride thin film transistors in the inverted staggered electrode structure, where the gate insulator and semiconductor are deposited sequentially by plasma enhanced chemical vapour deposition in the same growth apparatus.Localised electron states in the amorphous silicon are crucial in determining transistor performance. Conduction band states (Si-Si antibonding σ*) are broadened and localised in the amorphous network, and their energy distribution determines the field effect mobility. The silicon dangling bond defect is the most important deep localised state and their density determines the prethreshold current and hence the threshold voltage. The density of states is influenced by the gate insulator interface and there is probably a decreasing density of states away from this interface. The silicon dangling bond defect in the bulk amorphous silicon nitride also leads to a localised gap state, which is responsible for the observed threshold voltage instability.Other key material properties include the fixed charge densities associated with primary passivating layers placed on top of the amorphous silicon. The low value of the bulk density of states in the amorphous silicon layer increases the sensitivity of device characteristics to charge at the top interface.

CORRELATION BETWEEN OPTICAL DEFECT DENSITY AND SPIN DENSITY IN AMORPHOUS SILICON CARBIDE

1991 ◽  
Vol 05 (04) ◽  
pp. 285-292 ◽  
Author(s):  
F. DEMICHELIS ◽  
C.F. PIRRI ◽  
E. TRESSO
Keyword(s):  
Silicon Carbide ◽  
Absorption Coefficient ◽  
Amorphous Silicon ◽  
Defect Density ◽  
Dangling Bond ◽  
Amorphous Silicon Carbide ◽  
Bond Density ◽  
Spin Resonance ◽  
Excess Absorption ◽  
Deposition Conditions

Amorphous silicon carbide (a-SiC:H) films deposited by different techniques under different deposition conditions have been submitted to photo-thermal deflection and photoacoustic spectroscopy (PDS and PAS) and electron spin resonance (ESR) measurements in order to obtain, through the trend of low energy absorption coefficient and the density of spins, information on the nature, energy and number of defects. The results obtained from the two techniques are often in disagreement since the dangling bond density generally does not scale with the integrated defect density. In order to explain the discrepancy the absorption coefficient has been calculated, following the Tauc model, in the three regions of fundamental absorption, Urbach tail and excess absorption. An expression for the density of defects has been obtained which depends on the integrated excess absorption coefficient through a proportionality factor.

Are there Charged Dangling Bonds in Device Quality Amorphous Silicon?

1993 ◽  
Vol 297 ◽  
Author(s):  
M.S. Brandt ◽  
A. Asano ◽  
M. Stutzmann
Keyword(s):  
Amorphous Silicon ◽  
Dangling Bond ◽  
Spin Resonance ◽  
Resonance Data ◽  
Different Temperatures ◽  
Impurity Doping ◽  
Small Density ◽  
Charged Defects ◽  
Hydrogenated Amorphous ◽  
Absorption Measurements

We discuss the possible existence of a considerable density of charged dangling bond defects in device-quality hydrogenated amorphous silicon, which for example has been postulated by recent thermal equilibrium models for the density-of-states distribution. Based on a quantitative analysis of spin resonance and light-induced spin resonance data at different temperatures as well as on subgap absorption measurements, we conclude that intrinsic a-Si:H only has a small density of charged defects caused by unintentional impurity doping. The same conclusion also holds for light-soaked a-Si:H and for samples which are dehydrogenated by annealing at high temperatures.

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