how does the mobility edge separate localized from non localized states?
Dear Naveen
Quantum states in valence band and conduction bands are non- localized states which are due to short range order present in non -crystalline materials. However, the band edges are not sharp but has tails of localized states due to the absence of long range order. Conduction in localized states is only by hopping using thermal energy. Mobility of charge carriers is zero at absolute zero temperature. A mobility edge can be defined in these materials as mobility drops to zero in localized states from some value in extended non- localized states. Quantum states due to defects present in non- crystalline materials also form localized states near Fermi level where also conduction is possible due to variable range hopping process as suggested by Mott.
Thank you Dr.A. kumar for your valuable answer. and these localized states can be formed by impurity and density of broken bonds in disordered structure?
Dear Naveen
Broken bonds may be quite large in number in non -crystalline semiconductors and they form localized states near Fermi level. Impurity incorporation in these materials not always produce electrically active centres and hence doping is difficult but not impossible. By reducing the defects by some special technique of preparation doping can be done. Hydrogenated amorphous silicon is good example where dangling bonds are saturated by Hydrogen present in the material and doping is possible.
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