Temperature dependence of ESR spectra of doped a‐Si:H

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Abstract
The temperature dependence of the ESR lines with g = 2.01 for boron‐doped and with g = 2.0043 for phosphorus‐doped a–Si:H, associated with singly occupied tail states of the valence and conduction band, respectively, is investigated. Both resonances broaden considerably with increasing temperature, and the broadening δHpp(T) is related with the electrical conductivity σ(T) as δHpp(T) = c[σ(T]n with 0.64 < n < 1. The g‐values of both lines decrease with rising temperature. The spin density N8 is for weakly boron‐doped samples constant at low temperatures, for phosphorus‐doped a‐Si: H, however, an increase of N8 with rising temperature is observed. These results are explained in a model with a small correlation energy ( U < kT) for the conduction band tail and a large one (U ≫ kT ) for the valence band tail. The temperature variation of the g‐value is ascribed to its energy dependence. Electrons in localized states near the mobility edges are assumed to have smaller g‐values than those in states with a larger energy distance from the edges. The relation between the line broadening δHpp(T) and the conductivity can be understood by spin relaxation of the localized electrons due to exchange coupling with rapidly relaxing carriers in extended states.