Determination of Density of Localized States in Amorphous Silicon Alloys From the Low Field Conductance of Thin N-I-N Diodes

1985 ◽  
Vol 49 ◽  
Author(s):  
Michael Shur ◽  
Michael Hack
Keyword(s):  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Bulk Density ◽  
Density Of States ◽  
Energy Gap ◽  
Localized States ◽  
New Technique ◽  
Silicon Alloys ◽  
Low Field ◽  
Density Of Localized States

AbstractWe describe a new technique to determine the bulk density of localized states in the energy gap of amorphous silicon alloys from the temperature dependence of the low field conductance of n-i-n diodes. This new technique allows us to determine the bulk density of states in the centre of a device, and is very straightforward, involving fewer assumptions than other established techniques. Varying the intrinsic layer thickness allows us to measure the,density of states within approximately 400 meV of midgap.We measured the temperature dependence of the low field conductance of an amorphous silicon alloy n-i-n diode with an intrinsic layer thjckness of 0.45 microns and deduced the density of localised states to be 3xlO16cm−3 eV−1 at approximately 0.5 eV below the bottom of the conduction band. We have also considered the high bias region (the space charge limited current regime) and proposed an interpolation formula which describes the current-voltage characteristics of these structures at all biases and agrees well with our computer simulation based on the solution of the complete system of transport equations.

Dark decay of surface potential: measurement of the density of localized states in highly resistive amorphous silicon alloys

1987 ◽  
Vol 97-98 ◽  
pp. 743-746 ◽  
Author(s):  
Y. Nakayama ◽  
H. Kita ◽  
T. Takahashi ◽  
S. Akita ◽  
T. Kawamura
Keyword(s):  
Amorphous Silicon ◽  
Surface Potential ◽  
Localized States ◽  
Silicon Alloys ◽  
Potential Measurement ◽  
Density Of Localized States ◽  
Dark Decay

Density of Deep Bandgap States in Amorphous Silicon From the Temperature Dependence of Thin Film Transistor Current

1994 ◽  
Vol 336 ◽  
Author(s):  
T. Globus ◽  
H. C. Slade ◽  
M. Shur ◽  
M. Hack
Keyword(s):  
Thin Film ◽  
Activation Energy ◽  
Amorphous Silicon ◽  
Conduction Band ◽  
Energy Gap ◽  
Localized States ◽  
Flat Band ◽  
Gate Bias ◽  
Density Of Localized States ◽  
Wide Range

ABSTRACTWe have measured the current-voltage characteristics of amorphous silicon thin film transistors (a-Si TFTs) over a wide range of temperatures (20 to 160°C) and determined the activation energy of the channel current as a function of gate bias with emphasis on the leakage current and subthreshold regimes. We propose a new method for estimating the density of localized states (DOS) from the dependence of the derivative of activation energy with respect to gate bias. This differential technique does not require knowledge of the flat-band voltage (VFB) and does not incorporate integration over gate bias. Using this Method, we have characterized the density of localized states with energies in the range 0.15–1.2 eV from the bottom of the conduction band and have found a wide peak in the DOS in the range of 0.8–0.95 eV below the conduction band. We have also observed that the DOS peak in the lower half of the bandgap increases in magnitude and shifts towards the conduction band as a result of thermal and bias stress. We also measured an overall increase in the DOS in the upper half of the energy gap and an additional peak, centered at 0.2 eV below the conduction band, which appear due to the applied stress. These results are in qualitative agreement with the defect pool Model [1,2].

ESR STUDIES OF GMR RELATED MATERIALS I: ESR of Mn IN LaMnO3 AND La0.99Ca0.01MnO3

2000 ◽  
Vol 14 (25n26) ◽  
pp. 883-897 ◽  
Author(s):  
N. ARAI ◽  
K. SUGAWARA
Keyword(s):  
Magnetic Susceptibility ◽  
Temperature Dependence ◽  
Spin System ◽  
High Field ◽  
Energy Gap ◽  
Low Field ◽  
High Field Esr ◽  
Clear Signal ◽  
Spin Clusters ◽  
G Value

ESR measurements are carried out for La 1-x Ca x MnO 3 (x=0, 0.01) from 760 K down to 4 K. A clear signal was observed above 260 K, presumably arising from Mn 3+ and Mn 4+, but two kinds of signals, the low-field and high-field ESR with g≃2, were observed below it. The high- and low-field signals are tentatively assumed to originate from Mn 4+ and Mn 3+, respectively. The g-value, linewidth, and intensity of the high-field signal nearly follow ∝1/(T-106). The temperature dependence of g-shift of the low-field signal is similar to that of magnetic susceptibility of LaMnO 3. The ESR intensity anomalously increases at temperatures between about 150 K and 250 K, which is tentatively ascribed to the occurrence of "spin-clusters". Above ≃300 K, the ESR intensity nearly follows Curie's law, and the linewidth is proportional to exp (-500/T), an indication of some kind of energy-gap existence in the Mn spin system.

New features of the temperature dependence of photoconductivity in plasma‐deposited hydrogenated amorphous silicon alloys

1981 ◽  
Vol 52 (8) ◽  
pp. 5235-5242 ◽  
Author(s):  
P. E. Vanier ◽  
A. E. Delahoy ◽  
R. W. Griffith
Keyword(s):  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Silicon Alloys ◽  
Hydrogenated Amorphous

Characteristics of Amorphous Silicon Based Alloy Field Effect Transistors

1984 ◽  
Vol 33 ◽  
Author(s):  
M. Shur ◽  
M. Hack ◽  
C. Hyun
Keyword(s):  
Amorphous Silicon ◽  
Field Effect ◽  
Energy Gap ◽  
Field Effect Transistors ◽  
Localized States ◽  
Flat Band ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
A New Technique ◽  
Silicon Based

ABSTRACTWe have developed a new theory to describe the current-voltage characteristics of amorphous silicon based alloy field effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap and that the field effect mobility is dependent on gate voltage. We also propose a new technique to determine the flat-band voltage from the I-V characteristics in the below threshold regime.

Optical absorption, disorder, and hydrogen in amorphous silicon

1996 ◽  
Vol 74 (S1) ◽  
pp. 256-259 ◽  
Author(s):  
Stephen K. O'Leary ◽  
Lakhbeer S. Sidhu ◽  
Stefan Zukotynski ◽  
John M. Perz
Keyword(s):  
Absorption Spectrum ◽  
Standard Deviation ◽  
Optical Absorption ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Hydrogen Concentration ◽  
Optical Absorption Spectrum ◽  
Energy Gap ◽  
Local Form ◽  
Absorption Data

We study how bonded hydrogen influences the optical absorption spectrum of amorphous silicon. We use a model for optical absorption in which the local form of the joint density of states is averaged over a Gaussian distribution of energy-gap fluctuations, this distribution being characterized by a mean energy gap and a standard deviation about this mean. We then fit this model to optical absorption data, and study how the modeling parameters vary with the bonded hydrogen concentration. We find that for the group of samples that we have considered, for bonded-hydrogen concentrations less than 10 at.%, we can adequately fit the data with a constant mean energy gap and a variable standard deviation that decreases with increasing bonded-hydrogen concentration. This suggests that bonded hydrogen plays a significant role in decreasing the amount of disorder in amorphous silicon.

Density of localized states in amorphous semiconductors

1989 ◽  
Vol 67 (4) ◽  
pp. 425-429 ◽  
Author(s):  
Louis de Ladurantaye ◽  
Yves Lépine ◽  
Laurent J. Lewis
Keyword(s):  
Linear Algebra ◽  
Density Of States ◽  
Transport Model ◽  
Amorphous Semiconductors ◽  
Localized States ◽  
Trap Level ◽  
Trap States ◽  
Density Of Localized States ◽  
Multiple Trapping ◽  
Photo Current

A procedure is described for extracting the density of localized states of amorphous semiconductors from transient photo-current measurements. Based on a discretized multiple-trapping transport model, our deconvolution scheme determines, for each trap level, the time–temperature combination such that the activity is a maximum for that level. The density of the trap states is then obtained using linear-algebra techniques. As an example, our procedure is applied to computer-generated signals obtained using an exponential density of states. The deconvoluted distribution of levels is found to be in excellent agreement with the original one.

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