Defects in Amorphous and Organic Semiconductors
- 4 Downloads
Amorphous and organic semiconductors have strong topological irregularities with respect to specific ideal structures, which depend on the particular class of such semiconductors. Most of these defects are rather gradual displacements from an ideal surrounding. The disorder leads to defects levels with a broad energy distribution which extends as band tails into the bandgap. Instead of a sharp band edge known from crystalline solids a mobility edge exists separating between extended states in the bands and localized states in the band tails.
Amorphous semiconductors, also referred to as semiconducting glasses, comprise the classes of amorphous chalcogenides and tetrahedrally bonded amorphous semiconductors. Amorphous chalcogenides are structurally floppy solids with low average coordination numbers and pronounced pinning of the Fermi level near midgap energy. The more rigid tetrahedrally bonded amorphous semiconductors have larger coordination numbers. They may be well doped p-type and n-type much like crystalline semiconductors.
Organic semiconductors comprise small-molecule crystals and polymers. Both have weak intermolecular bonds favoring deviations from ideal alignment. In small-molecule semiconductors the structure of thin films grown on substrates usually deviates from the structure of bulk crystals, with a substantially different molecule ordering at the interface and a strong dependence on the dielectric properties of the substrate. Polymers consist of long chain-like molecules packed largely uniformly in crystalline domains separated by amorphous regions with tangled polymer chains. Besides chemical structure of the chains crystallinity depends on the molecular length.
KeywordsAmorphous chalcogenides Anderson localization Anderson-Mott localization Band tails Coordination number Dangling bonds Defects Doping Localization Grain boundary Mobility edge Organic semiconductors Polymers Semiconducting glasses Small-molecule crystals Point defects Tailing of states Trap states Tetrahedrally bonded amorphous semiconductors Thin-film phase
- Adler D, Fritzsche H (eds) (1985) Tetrahedrally bonded amorphous semiconductors. Springer, New YorkGoogle Scholar
- Götze W (1981) The conductor-nonconductor transition in strongly disordered three-dimensional systems. In: Devreese JT (ed) Recent development in condensed matter physics. Plenum Press, New York, pp 133–154Google Scholar
- Koch FPV, Rivnay J, Foster S, Müller C, Downing JM, Buchaca-Domingo E, Westacott P, Yu L, Yuan M, Baklar M, Fei Z, Luscombe C, McLachlan MA, Heeney M, Rumbles G, Silva C, Salleo A, Nelson J, Smith P, Stingelin N (2013) The impact of molecular weight on microstructure and charge transport in semicrystalline polymer semiconductors–poly(3-hexylthiophene), a model study. Prog Polym Sci 38:1978CrossRefGoogle Scholar
- Mott NF (1969) Charge transport in non-crystalline semiconductors. In: Madelung O (ed) Festkörperprobleme/Advances in solid state physics, vol 9. Vieweg, Braunschweig, pp 22–45Google Scholar
- Mott NF, Davis EA (1979) Electronic processes in non-crystalline materials, 2nd edn. Oxford University Press, Oxford, UKGoogle Scholar
- Ovshinsky SR (1977) Chemical modification of amorphous chalcogenides. In: Proceedings of the 7th international conference on amorphous and liquid semiconductors, Edinburgh, pp 519–523Google Scholar
- Stuke J (1976) In: Kolomiets BT (ed) Electronic phenomena in non-crystalline solids. USSR Academy of Sciences, Leningrad, pp 193–202Google Scholar
- Varshishta P, Kalia RK, Nakano A, Li W, Ebbsjö I (1996) Molecular dynamics methods and large-scale simulations of amorphous materials. In: Thorpe MF, Mitkova MI (eds) Amorphous insulators and semiconductors. NATO ASI ser 3 high technology, vol 23. Kluwer Academic Publishers, Dordrecht, p 151Google Scholar
- Varshneya AK, Seeram AN, Swiler DR (1993) A review of the average coordination number concept in multicomponent chalcogenide glass systems. Phys Chem Glasses 34:179Google Scholar
- Wooten F, Weaire D (1989) Modelling tetrahedrally bonded random networks by computer. In: Ehrenreich H, Turnbull D (eds) Solid state physics, vol 40. Academic Press, New York, pp 1–42Google Scholar