  Transport properties of a series of poly(3-hexylthiophene) organic field
effect transistors with Cr, Cu and Au source/drain electrodes were examined
over a broad temperature range. The current-voltage characteristics of the
injecting contacts are extracted from the dependence of conductance on channel
length. With reasonable parameters, a model of hopping injection into a
disordered density of localized states, with emphasis on the primary injection
event, agrees well with the field and the temperature dependence of the data
over a broad range of temperatures and gate voltages.
