title: Temperature-independent hole mobility of a smectic liquid-crystalline semiconductor based on band-like conduction.
abstract: A liquid-crystalline (LC) phenylterthiophene derivative, which exhibited an ordered smectic phase at room temperature, was purified by vacuum sublimation under a flow of nitrogen. During the sublimation process, thin plates with sizes of 1 mm grew on the surface of the vacuum tube. The crystals exhibited the same X-ray diffraction patterns as the ordered smectic phase of the LC state that was formed through a conventional recrystallization process by using organic solvents. Because of the removal of chemical impurities, the hole mobility in the ordered smectic phase of the vacuum-grown thin plates increased to 1.2×10(-1) cm(2) V(-1) s(-1) at room temperature, whereas that of the LC precipitates was 7×10(-2) cm(2) V(-1) s(-1). The hole mobility in the ordered smectic phase of the vacuum-sublimated sample was temperature-independent between 400 and 220 K. The electric-field dependence of the hole mobility was also very small within this temperature range. The temperature dependence of hole mobility was well-described by the Hoesterey-Letson model. The hole-transport characteristics indicate that band-like conduction affected by the localized states, rather than a charge-carrier-hopping mechanism, is a valid mechanism for hole transport in an ordered smectic phase.
authors.affiliation: Department of Advanced Materials Science, Faculty of Engineering, Kagawa University, 2217-20 Hayashi-cho, Takamatsu, Kagawa 761-0396, Japan. m-funa@eng.kagawa-u.ac.jp
authors.forename: Masahiro
authors.initials: M
authors.lastname: Funahashi
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ishii
authors.forename: Akinari
authors.initials: A
authors.lastname: Sonoda
mesh_terms: D050866:Liquid Crystals / Q000737:chemistry*; D011789:Quantum Theory; D012666:Semiconductors; D013696:Temperature; D013876:Thiophenes / Q000737:chemistry
chemical_list: D013876:Thiophenes; C019101:alpha-terthienyl
keywords: crystal growth; hole mobility; liquid crystals; semiconductors; thiophenes