Proceedings Article | 13 September 2007
KEYWORDS: Crystals, Silicon, Transistors, Microcrystalline materials, Resistors, Organic materials, Thin films, Field effect transistors, Temperature metrology, Dielectrics
Several organic and inorganic materials have emerged as promising candidates for the active layer of field-effect
transistors (FETs) fabricated on flexible substrates. The charge transport models necessary for device optimization in
these systems are at different stages of development. The understanding of charge transport in single-crystal and thin-film
FETs based on organic materials such as pentacene, rubrene, and other related compounds has advanced
considerably in recent years and a clear picture of the relevant transport mechanisms is forming. In contrast, the
theoretical description of transport in hydrogenated microcrystalline silicon (μc-Si:H) is not as well known and the
published results and theories are often contradictory. We review the paradigms we feel are useful in describing the
current understanding of transport in organic and μc-Si:H field-effect transistors. In the case of organic materials these
include the polarization and transfer integral fluctuation model [A. Troisi and G. Orlandi, Phys. Rev. Lett. 96, 086601
(2006), J.-D. Picon et al., Phys. Rev. B 75, 235106 (2007)], the Frölich polaron model [I.N. Hulea et al., Nat. Mater. 5,
982 (2006), H. Houilli et al., J. Appl. Phys. 100, 033702 (2006)], and several trapping models [M.E. Gershenson et al.,
Rev. Mod. Phys. 78, 973 (2006), V. Podzorov et al., Phys Rev. Lett. 95, 226601 (2005)]. Given the heterogeneous
composition and structure of microcrystalline silicon thin films, a variety of theories to describe dark conductivity have
been applied to μc-Si:H including those based on percolation theory [H. Overhof et al., J. Non-Cryst. Solids 227-230,
992 (1998)], hopping models [A. Dussan and R. H. Buitrago, J. Appl. Phys. 97, 043711 (2005)], thermionic emission,
and tunneling. We give a brief overview of these models and present a fluctuation-induced tunneling model that we are
developing to describe charge transport in microcrystalline silicon.
