  We perform a combined experimental and theoretical study of
tetramethyltetraselenafulvalene (TMTSF) single-crystal field-effect
transistors, whose electrical characteristics exhibit clear signatures of the
intrinsic transport properties of the material. We introduce a simple,
well-defined model based on physical parameters and we successfully reproduce
quantitatively the device properties as a function of temperature and carrier
density. The analysis allows its internal consistency to be checked, and
enables the reliable extraction of the density and characteristic energy of
shallow and deep traps in the material. Our findings indicate that shallow
traps originate from electrostatic potential fluctuations generated by charges
fixed in the deep traps.
