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.

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.

Application of Fermi-level analysis to the investigation of localized states distribution in the energy gap of vitreous As2S3

1972 ◽  
Vol 11 (1) ◽  
pp. K43-K45 ◽  
Author(s):  
A. M. Andriesh ◽  
S. D. Shutov ◽  
M. S. Iovu
Keyword(s):  
Fermi Level ◽  
Energy Gap ◽  
Localized States ◽  
Level Analysis

scholarly journals Limitation of Fermi level shifts by polaron defect states in hematite photoelectrodes

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Christian Lohaus ◽  
Andreas Klein ◽  
Wolfram Jaegermann
Keyword(s):  
Fermi Level ◽  
Defect States ◽  
Level Shifts

Temperature Dependent Defect Density Calculated from Activated Conductivity of a-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
T. Drusedau ◽  
V. Kirbs ◽  
H. Fiedler
Keyword(s):  
Fermi Level ◽  
Density Of States ◽  
Defect Density ◽  
State Density ◽  
Level Shift ◽  
Defect State ◽  
Temperature Dependent ◽  
Slow Cooling ◽  
Thermally Activated ◽  
Gap States

ABSTRACTThermally activated conductivity of a—Si:H at a slow cooling rate of 0.3 K/min is connected with temperature dependent changes of the mobility gap states. By means of the Fermi—level shift calculated from these data and a density of states model it is possible to determine this dependence. The results mainly reveal a decrease of the defect state density by about a tenth between 375 K and 400 K.

Investigation on the Gap Density of States in Amorphous Semiconducting Carbon Silicon and Carbon Tin Alloys

1987 ◽  
Vol 97 ◽  
Author(s):  
P. Mpawenayo ◽  
M. Nsabimana
Keyword(s):  
Spectral Analysis ◽  
Density Of States ◽  
Decay Time ◽  
Urbach Energy ◽  
Localized States ◽  
Semiconducting Materials ◽  
Defect States ◽  
Tin Alloys ◽  
Distribution Parameters ◽  
Gap States

ABSTRACTThe density of states in a-Six C1-x:H and a-Cy Sn1-y:H (F) semiconducting materials has been investigated by phototheTmal deflection spectroscopy (PDS) and their photoconductive properties have been related to the gap states distribution parameters, the Urbach energy Eo and the localized states density gm. We found that an Eo of 200 meV is the highest value above which no photoconductivity can be detected. This threshold corresponds to a density of gap states of about 1019 eV−1 cm−3 for optical gaps ranging between 1.1 and 2.5eV. Fourier spectral analysis of the long photoresponse decay time observed in our fluorinated a-Cy, Sn1-y samples shows the existence of well defined trapping levels and randomly distributed defect states.

Comparative studies of the influence of hydrogen incorporation on the electronic properties of a-Ge:H films prepared by two different techniques

2000 ◽  
Vol 77 (9) ◽  
pp. 659-666
Author(s):  
Y Bouizem ◽  
J D Sib ◽  
L Chahed ◽  
M L Thèye
Keyword(s):  
Optical Absorption ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Localized States ◽  
Optical Absorption Spectra ◽  
Defect States ◽  
Hydrogen Incorporation ◽  
Gap States ◽  
Hydrogenated Amorphous ◽  
Hydrogenated Amorphous Germanium

We present the results of a detailed investigation of hydrogen incorporation and optical absorption in the 0.6-1.3 eV range for two series of hydrogenated amorphous germanium films (a-Ge:H) deposited by reactive sputtering (series A) and by plasma-enhanced chemical vapor deposition from germane (series B). Our results clearly show that the series A samples are characterized by a larger bonded hydrogen concentration (CH), a more rapid gap variation with increasing CH, a smaller refractive index, and a lower density than the series B samples. We also compare in detail the energy distribution of the localized states in the pseudo-gap and the deep-defect states density as deduced from a decomposition of the optical absorption spectra based on a theoretical model for the gap states density in amorphous tetracoordinated semiconductors.PACS No.: 71.90

scholarly journals Author Correction: Limitation of Fermi level shifts by polaron defect states in hematite photoelectrodes

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Christian Lohaus ◽  
Andreas Klein ◽  
Wolfram Jaegermann
Keyword(s):  
Fermi Level ◽  
Defect States ◽  
Level Shifts

Quantum-kinetic Theory of Defect-mediated Recombination in Nanostructure-based Photovoltaic Devices

2013 ◽  
Vol 1493 ◽  
pp. 91-96 ◽  
Author(s):  
Urs Aeberhard
Keyword(s):  
Thin Film ◽  
Energy Gap ◽  
Photovoltaic System ◽  
Quasi Equilibrium ◽  
The Novel ◽  
Photovoltaic Devices ◽  
Novel Approach ◽  
Gap States ◽  
Non Equilibrium Green’S Function ◽  
Kinetic Treatment

ABSTRACTIn this paper, a quantum-kinetic equivalent of Shockley-Read-Hall recombination is derived within the non-equilibrium Green's function formalism for a photovoltaic system with selectively contacted extended-state absorbers and a localized deep defect state in the energy gap. The novel approach is tested on a homogeneous bulk absorber and then applied to a thin film photo-diode with large built-in field in the defect-rich absorber region. While the quantum-kinetic treatment reproduces the semi-classical characteristics for a bulk absorber in quasi-equilibrium conditions, for which the latter picture is valid, it reveals in the thin film case non-classical characteristics of recombination enhanced by tunneling into field-induced sub-gap states.

Enhancing the Power Conversion Efficiency of Inverted Organic Photovoltaics with Gold Functionalized Reduced Graphene Oxide

2015 ◽  
Vol 1737 ◽  
Author(s):  
Rebecca Isseroff ◽  
Zhenhua Yang ◽  
Jessica Kim ◽  
Andrew Chen ◽  
Miriam Rafailovich
Keyword(s):  
Graphene Oxide ◽  
Fermi Level ◽  
Reduced Graphene Oxide ◽  
Active Layer ◽  
Energy Gap ◽  
Power Conversion ◽  
Design Phase ◽  
Reduced Graphene ◽  
Exciton Recombination ◽  
First Time

ABSTRACTIn this study, an “inverted” design, phase-separated morphology and gold-functionalized reduced graphene oxide (Au-rGO) were used to address exciton recombination and poor Fermi level alignment. To increase efficiencies, a unique methodology was used to coat Au-rGO on top of the active layer. When 0.05 Au-rGO was blended with the active layer, there were metal-thiolate bonds with P3HT and π-π stacking with PCBM. However, KPFM, measured for the first time for this material, showed that the while 0.05mM Au-rGO reduced the energy gap between P3HT and PBCM, this was offset by recombination. KPFM showed that Au-rGO may be better suited between the active layer and electrode. When 0.5mM Au-rGO was coated on top of the active layer, efficiency increased (p<0.002) nearly 600%, suggesting that Au-rGO is a more effective acceptor than a constituent of the active layer.

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.

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