At high temperatures, one may get a thermal activation energy roughly half the optical band gap, corresponding to thermal excitation of carriers into nearest mobility edge. But in addition, how to interpret a much lower activation energy at lower temperatures ? If the latter is related to mid-gap states, how to determine the mechanism of carrier transport ?
Dear Manoj Kumar Jana
Have a nice time and good day
The dc-electrical conductivity is strongly dependent on the temperature and there are different conduction mechanisms can be observed. The conductivity can be given by the Arrhenius equation. It contains two terms (sometimes it contains three terms) and they arise from two different conduction mechanisms. The first term describes the high temperature region and the dominant mechanism is the band conduction through the extended states.The second term of Arrhenius equation describes the conduction process at the lower temperature region. The hopping conduction via localized states is responsible for the conduction process in this region. Here the conductivity arises from tunneling through unoccupied levels of the nearest neighboring center. The pre-exponential factors (σo) and (σ1)of Arrhenius Eq. strongly depends on the composition and their values contribute to know the type of the conduction mechanism. The value of σ1 is approximately 102–104 times less than σo, partly because of the low density and mobility of delocalized states. Taking the logarithm of both sides of Arrhenius Eq. and plotting a graphical relationship between ln(σ) and (1000/T), it can get the activation energies from the slope of the obtained straight lines for the two conduction regions. The preexponential factors can be also obtained from the interception part of the extrapolation of the obtained straight lines with ln(σ)-axis.
The mechanism exists in the higher temperature region is the hopping conduction via localized states, while in the lower temperature region is the hopping conduction near the Fermi level. These two mechanisms were discussed as well as many another details were explained in my paper which has the title:
Electrical transport properties and Mott's parameters of chalcogenide cadmium sulphoselenide bulk glasses.
You can go to this link, it will help you.
Good Luck
https://www.researchgate.net/publication/283421231_Electrical_transport_properties_and_Mott's_parameters_of_chalcogenide_cadmium_sulphoselenide_bulk_glasses [accessed May 24, 2016].
Article Electrical transport properties and Mott's parameters of cha...
Dear Manoj Kumar Jana
Have a nice time and good day
This paper also discuss the conduction mechanisms in the two mentioned regions. It may help you dear.
My regards
https://www.researchgate.net/publication/223793330_Optical_and_electrical_properties_of_Ge10xSe40Te50-x_thin_film
Article Optical and electrical properties of Ge10+xSe40Te50−x thin film
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