On the Origin of the Urbach Rule and the Urbach Focus

2013 ◽  
Vol 1536 ◽  
pp. 139-145 ◽  
Author(s):  
J. A. Guerra ◽  
L. Montañez ◽  
F. De Zela ◽  
A. Winnacker ◽  
R. Weingärtner
Keyword(s):  
Optical Absorption ◽  
Amorphous Semiconductors ◽  
Absorption Process ◽  
Exponential Tail ◽  
Simple Derivation ◽  
Exponential Tails ◽  
Average Transition ◽  
Theoretical Results ◽  
Experimental Absorption ◽  
Phonon Model

ABSTRACTA simple derivation of sub-bandgap exponential tails and fundamental absorption equations ruling the optical absorption of amorphous semiconductors are presented following the frozen phonon model. We use the Kubo-Greenwood formula to describe the average transition rate for the optical absorption process. Asymptotic analysis leads to the commonly observed exponential tail as well as the Tauc expression for the fundamental absorption. We test our theoretical results with experimental absorption coefficients of amorphous Si:H, SiC:H, AlN and SiN. The validity of the Urbach focus concept is evaluated.

Optical Transitions in Chalcogenide Glasses From the Point of View of a Barrier-Cluster Model

2008 ◽  
Vol 39-40 ◽  
pp. 253-256
Author(s):  
Ivan Baník
Keyword(s):  
Optical Absorption ◽  
Low Temperatures ◽  
Cluster Model ◽  
Chalcogenide Glasses ◽  
Temperature Shift ◽  
Point Of View ◽  
Optical Transitions ◽  
Influence Of Temperature ◽  
Exponential Tails ◽  
Influence Of Temperature On

A barrier-cluster model of chalcogenide glasses is employed to analyze optical transitions near the absorption edge. The influence of temperature on the optical absorption is studied. The model is used to explain the temperature shift of exponential tails of the optical absorption and the temperature dependence of the optical forbidden-band width at low temperatures.

Interband optical absorption in amorphous semiconductors

1984 ◽  
Author(s):  
Morrel H. Cohen ◽  
Costas M. Soukoulis ◽  
E. N. Economou
Keyword(s):  
Optical Absorption ◽  
Amorphous Semiconductors

Optical absorption in amorphous semiconductors

1985 ◽  
Vol 77-78 ◽  
pp. 171-174 ◽  
Author(s):  
M.H. Cohen ◽  
C.M. Soukoulis ◽  
E.N. Economou
Keyword(s):  
Optical Absorption ◽  
Amorphous Semiconductors

An explanation of optical phenomena in non-crystalline semiconductors

Open Physics ◽  
2005 ◽  
Vol 3 (2) ◽  
Author(s):  
Ivan Banik
Keyword(s):  
Optical Absorption ◽  
Transport Properties ◽  
Electric Transport ◽  
Potential Barriers ◽  
Parabolic Profile ◽  
Crystalline Semiconductor ◽  
Exponential Tails ◽  
Optical Phenomena ◽  
Barrier Model

AbstractBarrier model of a non-crystalline semiconductor is described in this article. The most important optical phenomena, which are typical for this group of materials, are explained on the base of this model. The model assumes that in non-crystalline semiconductors the potential barriers exist, which separate certain microscopic areas from each other, assuming barriers possess a parabolic profile. This conception explains the rise of exponential tails of optical absorption at the end of optical edge as well as electroabsorption, photoelectric conductivity, photoluminescence, and others. Using this model, many electric transport properties of non-crystalline semiconductors can be explained successfully.

Comparison of photoconductivity and optical absorption spectra of trapped electrons in γ-irradiated 2,2,4-trimethylpentane/2,2-dimethylbutane/2-methyltetrahydrofuran mixture glasses at 77 K

1984 ◽  
Vol 62 (1) ◽  
pp. 64-68 ◽  
Author(s):  
Toyoaki Kimura ◽  
Kazunobu Hirao ◽  
Naoto Okabe ◽  
Kenji Fueki
Keyword(s):  
Absorption Spectrum ◽  
Optical Absorption ◽  
Absorption Spectra ◽  
Electron Mobility ◽  
Optical Absorption Spectrum ◽  
Lower Energy ◽  
Photon Absorption ◽  
Optical Absorption Spectra ◽  
Absorption Process ◽  
Trapped Electrons

Optical absorption and photoconductivity spectra of trapped electrons in -γ-irradiated 2,2,4-trimethylpentane (TMP)/2,2-dimethylbutane (DMB)/2-methyltetrahydrofuran (MTHF) mixture glasses at 77 K have been measured. It is found that the magnitude of the photocurrent increases with decreasing MTHF concentration, which is ascribed to the increase in electron mobility with decreasing MTHF concentration in TMP/DMB/MTHF systems. It is also found that the photoconductivity spectra shift to the lower energy side with decreasing MTHF concentration. Although the photoconductivity spectrum in the neat MTHF system is separated from the corresponding optical absorption spectrum, the spectrum becomes closer to the latter with decreasing MTHF concentration in TMP/DMB/MTHF systems. This result indicates that the extent of bound–free transitions increases relative to bound–bound transitions with decreasing MTHF concentration for the photon absorption process of trapped electrons in TMP/DMB/MTHF systems.

Scattering and Absorption of Infrared Light on EL2 Clusters in GaAs Semi-Insulating Materials

1986 ◽  
Vol 69 ◽  
Author(s):  
J. P. Fillard ◽  
M. Castagne ◽  
J. Bonnafe ◽  
P. Gall
Keyword(s):  
Low Temperature ◽  
Optical Absorption ◽  
Infrared Light ◽  
Absorption Process ◽  
Infrared Transmission ◽  
Optical Contrast ◽  
Insulating Materials ◽  
Cell Patterns ◽  
Typical Cell ◽  
Center Density

AbstractIt is known that dislocations and EL2 clusters participate in infrared transmission images. Optical quenching of the typical cell patterns at low temperature also charge EL2 with contributing to images. A point yet is not clearly established: such optical contrast could originate in a quantum absorption process or as well in a scattering of the photons. This paper aims at showing that both optical processes are likely to occur in most of the GaAs SI samples and that the two phenomenons can be considered as localy correlated. So monitoring EL2 center density by optical “absorption” could be a trap for the unwarry.

Semiclassical density-of-states and optical-absorption analysis of amorphous semiconductors

1995 ◽  
Vol 51 (7) ◽  
pp. 4143-4149 ◽  
Author(s):  
Stephen K. O’Leary ◽  
Stefan Zukotynski ◽  
John M. Perz
Keyword(s):  
Optical Absorption ◽  
Density Of States ◽  
Amorphous Semiconductors ◽  
Absorption Analysis

scholarly journals A Short Theoretical Note on Optical Absorption of Amorphous Gallium Arsenide in the Infrared Range

1998 ◽  
Vol 20 (3) ◽  
pp. 139-142 ◽  
Author(s):  
M. A. Grado-Caffaro ◽  
M. Grado-Caffaro
Keyword(s):  
Gallium Arsenide ◽  
Optical Absorption ◽  
Absorption Coefficient ◽  
Far Infrared ◽  
Optical Absorption Coefficient ◽  
Infrared Range ◽  
Structural Disorders ◽  
Theoretical Results

An approach to determine the optical absorption coefficient of amorphous GaAs in the far infrared range is developed. Results from this approach are compared with experiment and with other theoretical results. In our formulation, contributions corresponding to both dynamical and structural disorders are taken into consideration.

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