Localized gap states in amorphous semiconducting compounds

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Abstract
Localized singly occupied gap states as evidenced by variable range hopping (resistivity proportional to exp T −1/4) have been observed in several amorphous semiconducting compounds deposited at 77 K. The presence of these states has been confirmed in several cases (GaAs, As2Te3 and As4Te3Se3) by susceptibility and E.S.R. experiments. The number of localized singly occupied states is appreciably reduced by annealing as shown by resistivity, susceptibility and E.S.R. experiments. The presence or absence of localized singly occupied gap states depends on the state of disorder of the amorphous solid (quenched from the melt, deposited at 77 K or annealed) and on the type of chemical bond present in the compound.