Exponential tails in the density of states

E. N. Economou, N. Bacalis, M. H. Cohen

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


The exponential tails in the density of states in amorphous tetrahedral films, chalcogenide glasses, and ionic crystals are associated with local states bound in single potential "wells". The exponential distribution is due (a) to the Gaussian distribution of the depths of the single potential "wells", and (b) to an approximately linear relation between the binding energy and the square of the depth of the potential well. This simple picture accounts for the qualitative features of the Urbach tails and it is consistent with quantitative data in a-Si:H, As2Se3, and in ionic crystals. Various levels of refinement of this simple picture have been worked out by us and our collaborators. These refinements provide quantitative improvement in the Urbach region, and extend the validity of our treatment to the Halperin-Lax and Tauc regions as well as the extremely deep states.

Original languageEnglish (US)
Pages (from-to)101-104
Number of pages4
JournalJournal of Non-Crystalline Solids
Issue numberPART 1
StatePublished - Dec 2 1987
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Materials Chemistry


Dive into the research topics of 'Exponential tails in the density of states'. Together they form a unique fingerprint.

Cite this