PULSE PHOTOCONDUCTIVITY IN VACUUM-DEPOSITED THIN-FILMS OF ALPHA-METAL-FREE PHTHALOCYANINE WITH INHOMOGENEOUS TRAP CONCENTRATION

By using pulsed photoconductivity techniques, transient action spectra on vacuum-sublimed alpha-metal-free phthalocyanine thin films have be en obtained in the wavelength range 350-700 nm. The transient photocur rents have been determined at field strengths lower than 10(7) V m-1 b y the range-limited carrier transport with spatially distributed traps , the mutau product of photogenerated holes in the sample varying from about 4 X 10(-15) to 2 X 10(-13) m2 V-1 and the electron mutau produc t being approximately 6 X 10(-16) m2 V-1. The inhomogeneity of the tra p concentration in the sample bulk was suggested to explain different shapes of the photoresponse spectra for different directions of the sa mple irradiation. The result indicates that spatial distribution of lo cal states can be approximated by the exponential function; local stat es are predominantly distributed in the vicinity of the substrate. A n ew method for determination of the spatial trap distribution parameter with resolution better than 0.1 mum is presented.