Electrical Conduction in Amorphous Trinitro - Nine - Fluorenone and Selenium
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Date
1992-06
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Addis Ababa University
Abstract
The theories of electronic structures in amorphous semiconductors
are reviewed. The effectiveness of the study of
electrical conductions particularly the SCLC, TSC and transient
photoconductivity, in providing a wealth of information on
electronic properties of disordered solids also discussed.
Analytic equations describing the above three conduction
properties are also developed. Experimental study of the SCLC,
TSC and transient photoconductivity is made fora_TNF and a-Se.
Distinctly from the models that are based on the assum~
tions of discrete or uniform distributions of traps in energy,
our experimental works on a~TNF and a-Se indicate the existence
of energetically dispersed charge carriers trapping states.
The observed space charge limited mode of conduction and its
temperature sensitivity is found to be best describable interms
of a smoothly varying distributions. The Gaussian distribution
seems more realistic for the interpretation of experimental
results in a~TNF and a~e.
Both hopping and multiple trapping models are used in
interpreting the transient photo-conductivity experimental
results for a-TNF and a.,.Se respectively. Drift mobilities of
charge carriers are seen to exhibit an activated nature and
also found to be field dependent in a manner similar to the
poole~Frenkel mechanism. For an explanation of the dispersive
hole transport in a-Se interms of the multiple trapping model,
the theoretical predictions developed on the basis of a
Gaussian distribution is found to agree with experimental
results more satisfactorily.
The study of thermally stimulated current characteristics
in a-TNF near the glass transition temperature, Tg, renders an
activation energy which is significantly different from results
of low temperature TSC analysis. Rather, it is nearly identical
to the zero field extrapolated activation energy computed
from transient photo conductivity experiments. There by
indicates this energy parameters to contain the disorder
induced term
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Keywords
Electrical Conduction in Amorphous