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.

Determination of the Density of States on N-type Ptcdi-c13 Organic Thin-film Semiconductor

2012 ◽  
Vol 1435 ◽  
Author(s):  
J. Puigdollers ◽  
A. Marsal ◽  
S. Galindo ◽  
P. Carreras ◽  
C. Voz ◽  
...  
Keyword(s):  
Density Of States ◽  
Field Effect Transistors ◽  
Localized States ◽  
Optical Absorption Coefficient ◽  
Organic Thin Film ◽  
Channel Conductance ◽  
Spectroscopy Technique ◽  
Photothermal Deflection Spectroscopy ◽  
Photothermal Deflection

ABSTRACTIn this paper we study the density of states in n-type N,N’-ditridecylperylene-3,4,9,10-tetracarboxylic diimide organic semiconductor using two different methods. The first one is based on the temperature dependence of the channel conductance in field-effect transistors. The second one is based on the subgap optical absorption coefficient measured using the Photothermal Deflection Spectroscopy technique. Both techniques allow estimating the distribution of localized states in the band gap of the semiconductor.

scholarly journals Conductivity and Density of States of New Polyphenylquinoline

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 934 ◽  
Author(s):  
Shamil R. Saitov ◽  
Dmitriy V. Amasev ◽  
Alexey R. Tameev ◽  
Vladimir V. Malov ◽  
Marine G. Tedoradze ◽  
...  
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Absorption Coefficient ◽  
Band Gap ◽  
Density Of States ◽  
Optical Band Gap ◽  
Dark Conductivity ◽  
Localized States ◽  
Energy Distance ◽  
Temperature Dependences

Electrical, photoelectrical, and optical properties of thin films of a new heat-resistant polyphenylquinoline synthesized using facile methods were investigated. An analysis of the obtained temperature dependences of the dark conductivity and photoconductivity indicates the hopping mechanism of conductivity over localized states arranging at the energy distance of 0.8 eV from the Fermi level located inside the band gap of the investigated material. The optical band gap of the studied material was estimated from an analysis of the spectral dependences of the photoconductivity and absorption coefficient before (1.8–1.9 eV) and after (2.0–2.2 eV) annealing at temperatures exceeding 100 °C. The Gaussian character of the distribution of the localized states of density inside the band gap near the edges of the bands was established. A mechanism of changes in the optical band gap of the investigating polymer under its annealing is proposed.

Optical stability of small-molecule thin-films determined by Photothermal Deflection Spectroscopy

2009 ◽  
Vol 1154 ◽  
Author(s):  
Marco Stella ◽  
Monica Beatriz Della Pirriera ◽  
Joaquim Puigdollers ◽  
Joan Bertomeu ◽  
Cristobal Voz ◽  
...  
Keyword(s):  
Thin Films ◽  
Absorption Coefficient ◽  
Small Molecule ◽  
Bulk Heterojunctions ◽  
Absorption Bands ◽  
Absorption Region ◽  
Air Exposure ◽  
Photothermal Deflection Spectroscopy ◽  
Photothermal Deflection ◽  
P Type

AbstractIn this paper the optical absorption properties of n-type C60 and PTCDA, and p-type CuPc small molecule semiconductors are investigated by optical transmission and Photothermal Deflection Spectroscopy (PDS). The results show the usual absorption bands related to HOMO-LUMO transitions in the high absorption region of the transmission spectra. PDS measurements also evidences exponential absorption shoulders with different characteristic energies. In addition, broad bands in the low absorption level are observed for C60 and PTCDA thin-films. These bands have been attributed to contamination due to air exposure. In order to get deeper understanding of the degradation mechanisms single and co-evaporated thin-films have been characterized by PDS. The dependence of the optical coefficient on exposure to light and air have been studied and correlated to the structural properties of the films (as measured by X-Ray Diffraction Spectroscopy). The results show that CuPc and PTCDA are quite stable against light and air exposure, while C60 shows important changes in its absorption coefficient. The bulk heterojunctions show stability in agreement with what observed for single layers, since the absorption coefficient of CuPc:PTCDA is almost not altered after the degradation treatments, while CuPc:C60 shows changes for low energy values.

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.

An Investigation of Photo-Induced Degradation by Means of Photothermal Deflection Spectroscopy

1987 ◽  
Vol 95 ◽  
Author(s):  
M. S. Bennett ◽  
S. Wiedeman ◽  
J. L. Newton ◽  
K. Rajan
Keyword(s):  
Optical Absorption ◽  
Fermi Level ◽  
Single Peak ◽  
Defect States ◽  
Hydrogenated Silicon ◽  
Photothermal Deflection Spectroscopy ◽  
Amorphous Hydrogenated Silicon ◽  
Measured Absorption ◽  
Photothermal Deflection

AbstractAbsorption measurements of as deposited and photodegraded intrinsic amorphous hydrogenated silicon films were made using photothermal deflection spectroscopy (PDS). The films were light-soaked in situ using HeNe laser light to simulate AM1 illumination. An increase in subbandgap absorption occurred predominantly near energies of 1.2eV. A simple model was developed in which a density of states function is hypothesized and the resulting optical absorption at subgap energies is calculated. The measured absorption could be well matched in all cases by assuming a single peak of defect states at or slightly below the Fermi level. Further, the observed changes in optical absorption due to degradation could be modeled by increasing the density of the single peak of defect states and moving the Fermi level towards the valence band.

Pulsed Photothermal Deflection Spectroscopy with Optically Dense Samples

1995 ◽  
Vol 49 (3) ◽  
pp. 279-285 ◽  
Author(s):  
Bingcheng Li ◽  
Yanzhuo Deng ◽  
Jieke Cheng
Keyword(s):  
Optical Absorption ◽  
Absorption Coefficient ◽  
Spectroscopic Data ◽  
Dynamic Range ◽  
Spectroscopic Measurement ◽  
Optical Absorption Coefficient ◽  
Power Fluctuation ◽  
Photothermal Deflection Spectroscopy ◽  
Photothermal Deflection ◽  
High Absorption

The pulsed photothermal deflection spectroscopy (PTDS) method to determine the large optical absorption coefficient from the transverse PTDS magnitude and to measure spectroscopic data of optically dense sample from the normal-to-transverse magnitude ratio of the PTDS signal is presented and has been examined both theoretically and experimentally. Saturation at high absorption, effects of thermal inhomogeneity of the sample, and energy or power fluctuation of both the excitation and probe beams are avoided by this method. Together with the transverse PTDS technique, the dynamic range of spectroscopic measurement is over 9 to 10 orders of magnitude. This technique can be used with sample which is transparent or semitransparent to the probe beam.

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