Temperature and Field Dependence of Hole Transport in Chloroaluminum Phthalocyanine Determined by Time-of-Flight Measurements

Abstract

Abstract Using the time-of-flight technique, drift mobility measurements were performed on the p-type semiconductor chloroaluminum phthalocyanine (C1AlPc). The field dependence of the hole mobilities was examined at different temperatures, and the results were found to be interpretable within the context of the disorder formalism developed by H. Bässler and coworkers. In the region of low applied fields the mobilities are seen to first decrease with increasing field, for all the temperatures in the range studied. The mobility then reaches a distinct minimum at intermediate fields which is followed by an increase at higher fields. The high field behaviour for all temperatures studied shows a linear dependence of In μ vs E1/2, the slope of which decreases with increasing temperature with values ranging from 9.15×10−3 (cm/V)1/2 at 265 K to 5.25×10−3 (cm/V)1/2 at 330 K. Mobilities at all applied fields were found to increase with rising temperatures showing a linear dependence of In μ vs T−2. At each temperature, measurements were taken for applied fields of 2.5×10−4 V cm−1 to 1.9×105 V cm−1. The mobilities at the highest applied field ranged from 6.05×10−5cm2V−1 s−1 at 265K to 1.15×10−4 cm2 V−1 s−1 at 330K. In view of the apparent consistency of this system's behaviour with that predicted by the disorder formalism, the relevant constants were calculated and their relationships examined to better determine the correlation with the proposed model. From μ (E=O) = μo exp-(To/T)2 and the appropriate plot, the values for μo and To are 2.5×10−3 cm2 V−1 s−1 and 777 K respectively. This yields a distribution width σ of 0.1 eV and corresponding values varying from 3.5 to 4.415 within the temperature range studied. Finally the parameter related to off-diagonal disorder, ∑, was found to be 1.58.