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.

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.

scholarly journals Density of Defect States and Spectra of Defect Absorption in a-Si:H

2019 ◽  
Vol 64 (4) ◽  
pp. 315
Author(s):  
R. G. Ikramov ◽  
M. A. Nuriddinova ◽  
R. M. Jalalov
Keyword(s):  
Absorption Coefficient ◽  
Density Of States ◽  
Spectral Characteristics ◽  
Localized States ◽  
Defect States ◽  
Hydrogenated Silicon ◽  
Principal Role ◽  
Electron Transitions ◽  
Amorphous Hydrogenated Silicon ◽  
Density Of Defect States

Spectral characteristics of the coefficient of defect absorption in amorphous hydrogenated silicon have been studied. The characteristics are determined, by analyzing the electron transitions occurring with the participation of the energy states of dangling bonds. It is shown that the principal role in the formation of the defect absorption coefficient value is played by the electron transitions between defect and non-localized states. It is also shown that the spectral characteristics are mainly determined by the distribution function of the electron density of states in the valence or conduction band. It is found that the maxima in the spectrum of the defect absorption coefficient are observed only if there are pronounced maxima in the density of states at the edges of allowed bands.

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

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.

Probing the Densities of Gap States in Intrinsic a-Si:H Using Space Charge Limited Currents of Electrons and Holes

1990 ◽  
Vol 192 ◽  
Author(s):  
Robin M. Dawson ◽  
J. H. Smith ◽  
C. R. Wronski
Keyword(s):  
Space Charge ◽  
Density Of States ◽  
Carrier Transport ◽  
Hydrogenated Amorphous Silicon ◽  
Wide Range ◽  
Self Consistent ◽  
Gap States ◽  
Hydrogenated Amorphous ◽  
Space Charge Limited Currents ◽  
Space Charge Limited

ABSTRACTSpace charge limited currents of holes in intrinsic hydrogenated amorphous silicon (a-Si:H) have been obtained using novel p+-intrinsic-p+ (p-i-p) structures. The presence of these hole space charge limited currents is verified from their temperature dependence and their dependence on a wide range of intrinsic layer thickness. The carrier transport and space charge limited currents in the p-i-p structures are compared with those of n-i-n structures and the results are discussed in terms of a self consistent density of states in the gap.

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.

scholarly journals Ab initioStudies of Electronic Structure of Defects in PbTe

2005 ◽  
Vol 864 ◽  
Author(s):  
Salameh Ahmad ◽  
Daniel Bilc ◽  
S.D. Mahanti ◽  
M.G. Kanatzidis
Keyword(s):  
Electronic Structure ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
Resonance State ◽  
Interesting Case ◽  
The Other ◽  
Defect States ◽  
Strong Resonance ◽  
Structure Calculations

AbstractAb initioelectronics structure calculations have been carried out in a series of RPb2n-1Te2n, n=16, compounds to understand the nature of “defect” states introduced by R where R = vacancy, monovalent Na, K, Rb, Cs, Ag atoms and divalent Cd atoms. We find that the density of states (DOS) near the top of the valence band and the bottom of the conduction band get significantly modified. The Na atom seems to perturb this region least (ideal acceptor in PbTe) and the other monovalent atoms enhance the DOS near the top of the valence band. Cd is an interesting case, since it introduces a strong resonance state near the bottom of the conduction band.

Nano-structured GeySi1-y:H Films Deposited by Low Frequency Plasma for Photovoltaic Application

2008 ◽  
Vol 1127 ◽  
Author(s):  
Andrey Kosarev ◽  
Alfonso Torres ◽  
Carlos Zuniga ◽  
Marco Adamo ◽  
Liborio Sanchez
Keyword(s):  
Electronic Properties ◽  
Urbach Energy ◽  
Low Frequency ◽  
Localized States ◽  
Statistical Parameters ◽  
Nano Structure ◽  
Mean Values ◽  
Temperature Dependence Of Conductivity ◽  
Wide Range ◽  
Grain Distribution

ABSTRACTIn this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured GeySi1-y:H films with y>0.5 prepared by low frequency (LF) PECVD. GeySi1-y:H films were deposited by LF PECVD at a frequency f= 110 kHz from SiH4+GeH4+H2 gas mixture. SiH4 and GeH4 flows were varied to fabricate the films in wide range of 0<y<l. Hydrogen dilution was varied in the range of RH =20 to 80. Structure of the films was studied by AFM and SEM with consequent image processing to extract statistical parameters such as grain distribution and mean values. Composition of the films was characterized by SIMS and EDX. Electronic properties were characterized by temperature dependence of conductivity, spectral dependence of optical absorption. Sub-gap absorption was characterized by Urbach energy, EU; and defect absorption, αD. We observed grain like nano-structure with Gauss distribution of grain diameters by both AFM and SEM measurements. The most interesting films had mean grain diameter<D> = 24.0±0.7 nm, dispersion D=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0.96-0.97(by SIMS and EDS). These films showed also the lowest values of Urbach energy EU = 0.030 eV and low defect absorption αD = 5×102 cm −1 (at photon energy hv = 1.04 eV) indicating on low density of localized states in mobility gap. Doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.

Diffuse reflectance spectroscopy: An effective tool to probe the defect states in wide band gap semiconducting materials

2018 ◽  
Vol 86 ◽  
pp. 151-156 ◽  
Author(s):  
Vikash Mishra ◽  
M. Kamal Warshi ◽  
Aanchal Sati ◽  
Anil Kumar ◽  
Vinayak Mishra ◽  
...  
Keyword(s):  
Band Gap ◽  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
Wide Band ◽  
Reflectance Spectroscopy ◽  
Semiconducting Materials ◽  
Defect States ◽  
Wide Band Gap

Urbach energy and the tails of the density of states in amorphous semiconductors

2011 ◽  
Vol 78 (2) ◽  
pp. 223-227 ◽  
Author(s):  
S. Zaynobidinov ◽  
R. G. Ikramov ◽  
R. M. Jalalov
Keyword(s):  
Density Of States ◽  
Urbach Energy ◽  
Amorphous Semiconductors
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