Surface state parameters of metal-free phthalocyanine single crystals

Abstract

Field-effect measurements have been performed on single crystals of metal-free phthalocyanine in high vacuum, hydrogen, and oxygen ambients. The effect of localized bulk states was taken into account. The usual field-effect analysis was modified to take into account the variation of the channel-to-gate potential along the channel. D.C. measurements indicate the presence of at least 10 11 cm −2 slow surface states. The time constant of these states is dependent on the ambient gas. Transient field-effect measurements indicate the presence of three sets of fast surface states having densities of 10 10−10 11 cm −2 within 0.17 eV of midgap. The parameters of these surface states are not appreciably affected by ambient gases. The thickness of the space-charge region of metal-free phthalocyanine crystals is 10 −5−10 −4 cm.