The bulk current in many single crystals of metalhyphen;free phthalocyanine has been found to exhibit Ohmic behavior up to fields of 104V/cm and squarehyphen;law dependence on voltage for higher fields. Photocurrents in these crystals were Ohmic over the entire range. If one interprets these results as spacehyphen;chargehyphen;limited currents (SCLC), trap densities of 1012to 1014/cm3are found from the temperature behavior of theIhyphen;Vcharacteristic. From the transition between Ohmic and squarehyphen;law regions, the concentration of free carriers was calculated to be approximately 106to 107/cm3in fairly good agreement with that found from Hall measurements. Samples were measured which had both dark and photo currents which varied asVat low fields, but asV1.5ndash;1.7at higher fields. These observations are interpreted qualitatively in terms of a model in which a layer of higher resistivity than the bulk extends from the contact into the bulk.
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