On the origin of the Urbach rule and the Urbach focus

J. A. Guerra, L. Montañez, F. De Zela, A. Winnacker, R. Weingärtner

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

11 Scopus citations


A 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.

Original languageEnglish
Title of host publicationFilm Silicon Science and Technology
Number of pages7
StatePublished - 2013
Event2013 MRS Spring Meeting - San Francisco, CA, United States
Duration: 1 Apr 20135 Apr 2013

Publication series

NameMaterials Research Society Symposium Proceedings
ISSN (Print)0272-9172


Conference2013 MRS Spring Meeting
Country/TerritoryUnited States
CitySan Francisco, CA


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