Carrier mobility for organic semiconductors: reduction of noise of the short part drift time in the time of flight mobility method.

Measurements of time of flight (TOF) mobility of organic semiconductors become difficult when the mobility values are high, since the electronic signals overlap with the noise of the short part in drift time. Such noise of the short part in the drift time in the TOF method for measurements of carrier mobility was reduced by three methods: (1) longer distance (3.5 m) between sample and the N(2) laser, (2) optical connection (photo coupler) between the N(2) laser and the pulse generator, and (3) using a digital filter to remove characteristic pulses caused by N(2) laser. Each method showed significant reduction of the noise. When all three methods were applied, 94% of the noise was reduced. The measurement of TOF mobility was demonstrated with TPD (N,N'-diphenyl-N,N'-di(meta-tolyl)benzidine) film. Electronic signals in TOF measurements were clearly observed and the TOF mobility was determined to be 9.0 x 10(-4) cm(2)/V s.