Photoconductivity study of amorphous CdTe

1977 ◽  
Vol 55 (3) ◽  
pp. 265-269 ◽  
Author(s):  
R. T. S. Shiah ◽  
D. E. Brodie ◽  
P. C. Eastman
Keyword(s):  
Light Intensity ◽  
Fermi Level ◽  
Conduction Band ◽  
Localized States ◽  
Effective Density ◽  
Transition Rates ◽  
Mobility Edge ◽  
Energy Parameters ◽  
Density Of Localized States ◽  
Mobility Gap

Photoconductivity measurements as a function of light intensity and temperature for amorphous CdTe are analyzed on the basis of the Mott and Davis model and some ideas of the Arnoldussen, Bube, Fagen, and Holmberg model. Energy parameters within the mobility gap of amorphous CdTe were evaluated. The effective density of localized states is found to be 1017and 1019 per cm3 per eV near the valence and conduction band edges respectively. The localized-to-localized recombination transition rates are also given. The dark Fermi level is found to be 0.54 eV above the valence mobility edge. Localized states extend into the mobility gap 0.37 eV from the valence mobility edge. These results are consistent with earlier measurements by Ng, Webb, and Brodie.

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].

The Meyer-Neldel Rule in Conductivity of Microcrystalline Silicon

2002 ◽  
Vol 715 ◽  
Author(s):  
Sanjay K. Ram ◽  
Satyendra Kumar ◽  
P. Rocai Cabarrocas
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Film Thickness ◽  
Fermi Level ◽  
Carrier Transport ◽  
Dark Conductivity ◽  
Localized States ◽  
Microcrystalline Silicon ◽  
Thermally Activated ◽  
Density Of Localized States

AbstractThe dark conductivity (σd) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (Ea) in all the samples. The Ea increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σo) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in Ea with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.

Effect of boron localized states on the conduction band transport in BxGa1−xP

2014 ◽  
Vol 105 (22) ◽  
pp. 222105 ◽  
Author(s):  
S. Petznick ◽  
L. Ostheim ◽  
P. J. Klar ◽  
S. Liebich ◽  
K. Volz ◽  
...  
Keyword(s):  
Conduction Band ◽  
Localized States

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.

scholarly journals Moderate strain induced indirect bandgap and conduction electrons in MoS2 single layers

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
János Pető ◽  
Gergely Dobrik ◽  
Gergő Kukucska ◽  
Péter Vancsó ◽  
Antal A. Koós ◽  
...  
Keyword(s):  
Charge Carrier ◽  
Fermi Level ◽  
Conduction Band ◽  
Carrier Density ◽  
Tensile Strain ◽  
Charge Carrier Density ◽  
Conduction Electrons ◽  
Metallic Character ◽  
Optical Bandgaps ◽  
Biaxial Tensile Strain

Abstract MoS2 single layers are valued for their sizeable direct bandgap at the heart of the envisaged electronic and optoelectronic applications. Here we experimentally demonstrate that moderate strain values (~2%) can already trigger an indirect bandgap transition and induce a finite charge carrier density in 2D MoS2 layers. A conclusive proof of the direct-to-indirect bandgap transition is provided by directly comparing the electronic and optical bandgaps of strained MoS2 single layers obtained from tunneling spectroscopy and photoluminescence measurements of MoS2 nanobubbles. Upon 2% biaxial tensile strain, the electronic gap becomes significantly smaller (1.45 ± 0.15 eV) than the optical direct gap (1.73 ± 0.1 eV), clearly evidencing a strain-induced direct to indirect bandgap transition. Moreover, the Fermi level can shift inside the conduction band already in moderately strained (~2%) MoS2 single layers conferring them a metallic character.

Defect states in amorphous Ge2Sb2Te5 phase change material

2014 ◽  
Vol 92 (7/8) ◽  
pp. 619-622
Author(s):  
N. Qamhieh ◽  
S.T. Mahmoud ◽  
A.I. Ayesh
Keyword(s):  
Fermi Level ◽  
Energy Gap ◽  
Continuous Distribution ◽  
Dark Conductivity ◽  
Localized States ◽  
Defect States ◽  
Thermally Activated ◽  
Level Shifts ◽  
Gap States ◽  
Change Material

Steady-state photoconductivity measurements in the temperature range 100–300 K on amorphous Ge2Sb2Te5 thin film prepared by dc sputtering are analyzed. The dark conductivity is thermally activated with a single activation energy that allocates the position of the Fermi level approximately in the middle of the energy gap relative to the valance band edge. The temperature dependence of the photoconductivity ensures the presence of a maximum normally observed in chalcogenides with low- and high-temperature slopes, which predict the location of discrete sets of localized states (recombination levels) in the gap. The presence of these defect states close to the valence and conduction band edges leaves the quasi Fermi level shifts in a continuous distribution of gap states at high temperatures, as evidenced from the γ values of the lux–ampere characteristics.

Accurate Reconstruction of the Density of States in a-Si:H by Photothermal and Photoconductive Spectra.

1993 ◽  
Vol 297 ◽  
Author(s):  
G. Amato ◽  
F. Giorgis ◽  
C. Manfredotti
Keyword(s):  
Iterative Method ◽  
Absorption Coefficient ◽  
Fermi Level ◽  
Density Of States ◽  
Localized States ◽  
Electronic Transitions ◽  
Photothermal Deflection Spectroscopy ◽  
Derivative Method ◽  
Photothermal Deflection ◽  
Made In

The distribution of occupied states in a-Si:H has been inferred by applying a new self- consisting iterative method to the absorption coefficient spectra. This procedure does not require any assumption about the localized states below the Fermi level, and provides a more accurate insight with respect to the simple derivative method. Numerical simulations have been made in order to probe the reliability of our method. The optical spectra have been obtained by means of Photothermal Deflection Spectroscopy (PDS) and Constant Photocurrent Method (CPM); the comparison between the results as obtained by the two techniques suggests that different sensitivities to electronic transitions are involved; this can be used to infer information about the unoccupied defects.

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