Temperature and field dependent mobility in pentacene-based thin film transistors

Pentacene-based thin film transistors (TFTs) have been fabricated and analyzed to investigate the temperature and electric field dependence of hole mobility. At room temperature, the TFT device characteristics have displayed the hole mobility of 0.26 cm²/V s, threshold voltage of -3.5 V, subthreshold slope of 2.5 V/decade, and on/off ratio of 10⁵. Over the temperature range of 300-450 K, the hole mobility is found to increase to a peak value, followed by decrease to very low values. Similar behavior has also been observed in TFTs fabricated at a higher pentacene deposition rate. However, in this case over 20 times reduction in the extracted hole mobility values has been observed, due to the less ordered layered structure of the pentacene film present. No annealing effects have also been observed up to a temperature of about 410 K. The field dependence of hole mobility has also been evaluated at room temperature, and observed to noticeably increase with increase in electric field, over the biasing conditions considered.