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The Conduction Mechanism of Self‐Compensated Highly Disordered Semiconductors (A Possible Model for Semiconducting Glasses)
Author(s) -
Böer K. W.
Publication year - 1969
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19690340235
Subject(s) - ambipolar diffusion , condensed matter physics , effective mass (spring–mass system) , semiconductor , fermi level , chalcogenide , band gap , quasi fermi level , hall effect , thermal conduction , electron mobility , conduction band , materials science , charge carrier density , direct and indirect band gaps , chemistry , electron , physics , electrical resistivity and conductivity , optoelectronics , doping , quantum mechanics , composite material
Ambipolar conduction in a self‐compensated highly disordered semiconductor with the Fermi‐level pinned close to the middle of the band gap is discussed and it is shown that predominant p‐type conduction occurs because of a higher effective level density in the narrower valence band, which usually is not compensated by a lower hole mobility due to a higher effective mass of holes. Because of a non‐negligible contribution of minority carriers, the Hall‐mobility is considerably lower than the actual carrier mobilities and can vanish and even invert its sign, if the major carrier transport takes place higher inside the bands where the effective masses increase markedly and/or if the Fermi‐level lies slightly above the middle of the band gap. The shift of the carrier transport into the bands is assumed to be caused by small potential barriers extending from the band edges into the band and being due to a sufficient density of charged centers. The results of this model are compared with experimental findings on a chalcogenide Ge 0.33 As 0.2 Te 0.2 S 0.27 ‐glass yielding m n = 0.2 m 0 , m p = 1.6 m 0 , μ n = 210 cm 2 /Vs, μ p = 75 cm 2 /Vs, n = 5 × 10 7 cm −3 , and p = 4 × 10 8 cm −3 for an observed semiconductivity of 5 × 10 −9 Ω −1 cm −1 and Hall‐mobility of −0.5 cm 2 /Vs at room temperature. The activation energy for semiconductivity is 0.72 eV, the optical band gap ≈ 0.9 eV, yielding a barrier height within the bands of ≈ 0.25 eV.