Examination of the Defect Pool Model by An Improved Analysis of the Constant Photocurrent Method

1995 ◽  
Vol 377 ◽  
Author(s):  
Helmut Stiebig ◽  
Frank Siebke
Keyword(s):  
Valence Band ◽  
Defect Density ◽  
Localized States ◽  
Optical Transitions ◽  
Defect States ◽  
Band Tail ◽  
Defect Distribution ◽  
Density Of Localized States ◽  
Pool Model ◽  
Extended States

ABSTRACTWe have developed an improved analysis of constant photocurrent method (CPM) data. It is based on a numerical simulation of CPM spectra taking into account the full set of optical transitions between localized and extended states, capture and emission processes as well as the position of the Fermi level. Comparing measured and simulated CPM spectra provides information about the density of localized states in a-Si:H, i.e. the valence band tail, the integrated defect density, the energy distribution and the charge state of defect states. Based on these results we examine the predictions of the defect-pool model. The defect distribution in undoped and doped a-Si:H can be described by the defect-pool model taking into account the doping level dependence of principal parameters including the valence band tail, the equilibration temperature, and the width of the defect-pool.

CPM and PDS - A Critical Interpretation of Experimental Results

1996 ◽  
Vol 420 ◽  
Author(s):  
Helmut Stiebig ◽  
Frank Siebke ◽  
Reinhard Carius
Keyword(s):  
Defect Density ◽  
Optical Transitions ◽  
Defect States ◽  
Defect Distribution ◽  
Urbach Tail ◽  
Yield Information ◽  
Pool Model ◽  
Neutral Defect ◽  
Critical Interpretation ◽  
Good Agreement

AbstractCPM and PDS spectra of a-Si:H yield identical shape of the Urbach tail, while the defect absorption measured by PDS differs significantly from CPM. In this work an analysis of CPM and PDS spectra of annealed and degraded films is presented. Numerical simulations of CPM and PDS data, taking into account optical transitions, capture and emission processes as well as the Fermi level, yield information on the energy distribution and the charge state of the defects. The simulations reveal the coexistence of defects in the D−, D+ and D0 states. The defect distribution is dominated by charged states as predicted by the defect-pool model. Good agreement between measured and simulated PDS and CPM spectra can be obtained in the case of a homogeneous defect density. It is shown that differences between CPM and PDS are due to different sensitivities of the techniques to charged and neutral defect states. Microscopic inhomogeneities may cause significant additional differences.

Sensitization of the Holes Lifetime by the Addition of Dangling Bonds in a-Si:H

2001 ◽  
Vol 664 ◽  
Author(s):  
L.F. Fonseca ◽  
S. Z. Weisz ◽  
I. Balberg
Keyword(s):  
Valence Band ◽  
Important Implication ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Defect States ◽  
Band Tail ◽  
Present Understanding

ABSTRACTThis paper is concerned with the phenomenon of the increase of the holes lifetime with the increase of the dangling bond concentration in a-Si:H. This rather surprising phenomenon that was observed, but not discussed, previously is shown to be a non-trivial effect which is based on the charged nature of the dangling bonds and a special scenario of the concentrations of the various defect states in the material. The most important implication of our study is that the charged dangling bonds can sensitize the valence band tail states, in contrast with the accepted roles of these types of states. The present understanding suggests that many new interesting phototransport phenomena can be found in a-Si:H.

Charge transport through localized states in sputtered amorphous silicon suboxides

2001 ◽  
Vol 666 ◽  
Author(s):  
J.J. van Hapert ◽  
N. Tomozeiu ◽  
E.E. van Faassen ◽  
A.M. Vredenberg ◽  
F.H.P.M. Habraken
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Rf Magnetron Sputtering ◽  
Quantitative Information ◽  
Thin Layers ◽  
Localized States ◽  
Variable Range Hopping ◽  
Defect States ◽  
Variable Range ◽  
Spin Resonance

ABSTRACTUsing an RF magnetron sputtering technique, thin layers (∼500 nm) of amorphous silicon suboxides (a-SiOx) were deposited, with oxygen/silicon ratios x ranging from 0 to 1.8. These layers contain a large density (1020−1021 cm−3) of, mostly silicon dangling bond, defect states. The level of conduction decreases several orders of magnitude with increasing x. The temperature dependence of the DC conductivity showed that the variable range hopping conduction mechanism is dominant for all x, over the temperature range 30- 330 K. In this mechanism the extent of localization and density of states around the Fermi level determine the conductance. We conclude that the decrease in conductance with increasing oxygen content must, for a large part, be due to a variation in the localization, since Electron Spin Resonance (ESR) measurements showed no decrease in defect density with increasing x. We performed DC conduction measurements at both low and high electric field strengths, showing phenomena, which are consistently desribed within the variable range hopping (VRH) model. These measurements allow the extraction of quantitative information, concerning both the localization and the density of the states involved in the hopping process.

States in the Gap of Improved a-Ge:H Studied by Photomodulation Spectroscopy

1991 ◽  
Vol 219 ◽  
Author(s):  
L. Chen ◽  
J. Tauc ◽  
D. Pang ◽  
W. A. Turner ◽  
W. Paul
Keyword(s):  
Glow Discharge ◽  
Valence Band ◽  
Density Of States ◽  
Pump Beam ◽  
Defect Density ◽  
Dangling Bond ◽  
Band Tail ◽  
Valence Bands

ABSTRACTThe photomodulation spectra of a-Ge:H of average photoelectronic quality(ημπ = 1 × 10-10cm2/V) and of improved quality (ημπ = 3 × 10-7cm2/V), produced under different plasma conditions in an r.f. diode reactor by glow discharge, were measured at 80K and are analyzed in analogy with earlier studies of a-Si:H. The spectra of the poorer material are dominated by transitions between dangling bond states and the conduction and valence bands. By contrast, the spectra of the better material require contributions of transitions from the band tail states, indicating that the reduced defect density has resulted in pump-beam induced quasi-Fermi levels reaching near the conduction and valence band edges. A very acceptable fit between plausible density-of-states distributions and the experimental spectra has been found.

The Interpretation of the Constant Photocurrent Method in Terms of Deep Defect Density of States in A-SI.H

1994 ◽  
Vol 336 ◽  
Author(s):  
Frank Siebke ◽  
Helmut Stiebig
Keyword(s):  
Electron Spin Resonance ◽  
Photoelectron Spectroscopy ◽  
Defect Density ◽  
Total Yield ◽  
Calibration Factor ◽  
Optical Transitions ◽  
Absolute Value ◽  
Spin Resonance ◽  
Pool Model

ABSTRACTThe constant photocurrent Method (CPM) is often used to measure the sub-bandgap absorption for the determination of the defect density. However, the absolute value of the derived defect density depends on the method of data analysis and the calibration factor. Normally the calibration factor is obtained from electron spin resonance (ESR) but the defect pool model gives rise to doubt whether ESR detects the same defects as CPm. Therefore, we propose combined total-yield photoelectron spectroscopy (TYPES) and CPM Measurements on n-type a-Si:H to determine the calibration factor. Furthermore, we calculate CPM spectra by extending an approach to simulate photoconductivity, taking into account the full set of optical transitions, and compare the results with standard evaluation Methods.

An Alternative Model for the Kinetics of Light-Induced Defects in A-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Paulo V. Santos ◽  
W. B. Jackson ◽  
R. A. Street
Keyword(s):  
Time Dependence ◽  
Valence Band ◽  
Defect Formation ◽  
Defect Density ◽  
Generation Rate ◽  
Band Tail ◽  
Defect Generation ◽  
Wide Range ◽  
Induced Defects ◽  
Kinetics Of

ABSTRACTThe kinetics of light-induced defect generation in a-Si:H was investigated over a wide range of illumination intensities and temperatures. The defect density around 1016cm-3 exhibits a power-law time dependence Ns ∼ G2εfε with ε = 0.2 to 0.3, where G is the photo-carrier generation rate. A model for the kinetics of defect generation is proposed based on the existence of an exponential distribution of defect formation energies in the amorphous network, associated with the valence band tail states. The model reproduces the observed time dependence of the defect density with an exponent e determined by the exponential width of the valence band tail. The temperature dependence of the defect generation rate is well-reproduced by the model, which provides a connection between the Stabler-Wronski effect and the weak-bond model.

I-V CHARACTERISTICS OF a-Si:H p-i-n Diodes with Uniform and Non-Uniform Defect Distributions

2000 ◽  
Vol 609 ◽  
Author(s):  
M.A. Kroon ◽  
R.A.C.M.M. van Swaaij ◽  
J.W. Metselaar
Keyword(s):  
Space Charge ◽  
Uniform Distribution ◽  
Charge Distribution ◽  
Defect States ◽  
Defect Distribution ◽  
Intrinsic Region ◽  
Current Voltage ◽  
Space Charge Distribution ◽  
Pool Model ◽  
Current Voltage Characteristics

ABSTRACTThis paper compares a-Si:H p-i-n diodes having a spatially uniform distribution of defect states with diodes in which the defect distribution is non-uniform, i.e. equilibrated according to the Defect-Pool model. Diodes with a uniform defect distribution exhibit a clear dependence of the current-voltage characteristics on the width of the intrinsic region, whereas in equilibrated diodes, this dependence is absent. This difference is explained by comparing the space-charge distribution and the recombination profile of the intrinsic region in both types of diodes.

Temperature Dependence of 1/f Noise and Electrical Conductivity Measurements on p-type a-Si:H Devices

2013 ◽  
Vol 1536 ◽  
pp. 181-186 ◽  
Author(s):  
V. C. Lopes ◽  
E. Hanson ◽  
D. Whitfield ◽  
K. Shrestha ◽  
C. L. Littler ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Valence Band ◽  
Hole Mobility ◽  
Type A ◽  
Localized States ◽  
Conductivity Measurements ◽  
Band Tail ◽  
Resistance Change ◽  
P Type

ABSTRACTNoise and electrical conductivity measurements were made at temperatures ranging from approximately 270°K to 320°K on devices fabricated on as grown Boron doped p-type a-Si:H films. The room temperature 1/f noise was found to be proportional to the bias voltage and inversely proportional to the square root of the device area. As a result, the 1/f noise can be described by Hooge’s empirical expression [1]. The 1/f noise was found to be independent of temperature in the range investigated even though the device conductivity changed by a factor of approximately 4 over this range. Conductivity temperature measurements exhibit a T-0.25 dependence, indicative of conduction via localized states in the valence band tail [2,3]. In addition, multiple authors have analyzed hole mobility in a-Si:H and find that the hole mobility depends on the scattering of mobile holes by localized states in the valence band tail [4-7]. We conclude that the a-Si:H carrier concentration does not change appreciably with temperature, and thus, the resistance change in this temperature range is due to the temperature dependence of the hole mobility. Our results are applicable to a basic understanding of noise and conductivity requirements for a-Si:H materials used for microbolometer ambient temperature infrared detection.

Thermal Equilibration Between Band Tail and Near Surface Defect States in Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys

1990 ◽  
Vol 192 ◽  
Author(s):  
Samer Aljishi ◽  
Shu Jin ◽  
Lothar Ley ◽  
Sigurd Wagner
Keyword(s):  
Valence Band ◽  
Photoelectron Spectroscopy ◽  
Silicon Germanium ◽  
Total Yield ◽  
State Density ◽  
Defect States ◽  
Band Tail ◽  
Characteristic Energy ◽  
Near Surface ◽  
Average Value

ABSTRACTWe employ total yield photoelectron spectroscopy to measure the density of occupied states at the clean a-SixGe1_x:H alloy surface. The near surface defect states are observed to lie at 0.57 eV above the valence band edge with a density of 4×l017 cm−3, independent of Ge content. The valence band tail characteristic energy is also measured to be independent of alloy composition with an average value of 54 meV. We demonstrate that thermodynamic equilibrium at the surface between weak bonds (forming the valence band tail) and the dangling bonds provides an excellent description of the experimental data and explains why the surface state density in a-Si:H cannot be lowered below the 1011 to 1012 cm−2 range.

Material Properties of a-SiGe:H Solar Cells as a Function of Growth Rate

2010 ◽  
Vol 1245 ◽  
Author(s):  
Peter Hugger ◽  
JinWoo Lee ◽  
J. David Cohen ◽  
Guozhen Yue ◽  
Xixiang Xu ◽  
...  
Keyword(s):  
Valence Band ◽  
Material Properties ◽  
Defect Density ◽  
Schottky Contact ◽  
Drive Level ◽  
Measurement Methods ◽  
Device Performance ◽  
Band Tail ◽  
Contact Devices ◽  
Defect Densities

AbstractWe have examined a series of a Si,Ge:H alloy devices deposited using both RF and VHF glow discharge in two configurations: SS/n+/i (a-SiGe:H)/p+/ITO nip devices and SS/n+/i (a-SiGe:H)/Pd Schottky contact devices, over a range of deposition rates. We employed drive-level capacitance profiling (DLCP), modulated photocurrent (MPC), and transient junction photo-current (TPI) measurement methods to characterize the electronic properties in these materials. The DLCP profiles indicated quite low defect densities (mid 1015 cm-3. to low 1016 cm-3 depending on the Ge alloy fraction) for the low rate RF (∼1Å/s) deposited a-SiGe:H materials. In contrast to the RF process, the VHF deposited a-SiGe:H materials did not exhibit nearly as rapid an increase of defect density with the deposition rate, remaining well below 1017 cm-3. up to rates as high as 10Å/s. Simple examination of the TPI spectra on theses devices allowed us to determine valence band-tail widths.. Modulated photocurrent (MPC) obtained for several of these a-SiGe:H devices allowed us to deduce the conduction band-tail widths. In general, the a-Si,Ge:H materials exhibiting narrower valence band-tail widths and lower defect densities correlated with the best device performance.

Sign in / Sign up

Export Citation Format

Share Document