Effect of shallow traps on polaron transport at the surface of organic   semiconductors
  The photo-induced electron and hole transfer across the semiconductor-dielectric interface in trap dominated p-type organic field-effect transistors (OFETs) has been investigated. It has been observed that the transfer of electrons into the dielectric results in a decrease of the field-effect mobility of polarons, suggesting that additional shallow traps are generated in the conduction channel. Using this effect, the dependence of the field-effect mobility on the density of shallow traps, mu(N), has been measured, which allowed to estimate the average polaron trapping time, tau_tr = 50 +- 10 ps, and the density of shallow traps, N_0 = (3 +- 0.5)*10^11 cm^-2, in the channel of single-crystal tetracene devices. 
M. F. Calhoun, C. Hsieh, V. Podzorov