The 25th International Conference on Amorphous and Nano-crystalline Semiconductors
August 18–23, 2013 Toronto, Ontario Canada
25th Anniversary Plenary Lecture V
Chair: Alla Reznik, Lakehead University
Theory of Charge Transport in Disordered Materials
Department of Physics and Material Sciences Centre, Philipps-Universität Marburg, Marburg D-35032, Germany
Charge transport in disordered semiconductors has been in the focus of ICALS – ICAS – ICAMS – ICANS meetings for almost 50 years. Chemistry and morphology of disordered semiconductors vary essentially for organic and inorganic materials existing in amorphous, microcrystalline, and nanocrystalline forms. Nevertheless charge transport properties of these chemically and morphologically different systems demonstrate striking similarities. There are in fact only two transport modes essential for disordered semiconductors: i) Band transport of charge carriers (electrons or polarons) mediated my trapping on spatially localized states; ii) Incoherent tunneling (hopping) of charge carriers between randomly distributed localized states.
Theoretical study of charge transport in disordered materials is currently often performed by empirical fitting of data obtained by numerical simulations. This is particularly true for research on organic semiconductors and on dye-sensitized systems. As a result of such empirical fitting, there is no agreement among researchers with respect to the appropriate theoretical description of the very key dependences of the carrier mobility μ on the concentration of localized states N, on the concentration of charge carriers n, on temperature T, and on the applied electric field F.
The main message of the talk is that transparent and reliable theoretical concepts for description of charge transport in disordered semiconductors suggested by N. F. Mott and his successors at rather early stages of research on disordered materials are still valid. It will be shown in the talk how these concepts can be successfully applied to describe charge transport, particularly to determine the dependences μ(N, n, T, F), in a broad variety of disordered semiconductors.
Keywords: hopping transport, mobility, density of states