Limitation on deep trapping of injected space charge in naphthalene and CdS monocrystals

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Abstract
Studies of space‐charge‐limited currents as a function of sample thickness L were made for CdS and naphthalene monocrystals. In naphthalene, where the current‐voltage curves show the behavior expected for a discrete trap energy above the Fermi level, we find VTFL essentially independent of L. We attribute this result to the presence of few filamentary regions oriented along the c axis and differing only slightly from the bulk in distribution of defects. For CdS we find VTFL ∝L, consistent with a constant upper field limit of 1.6 × 104 V/cm on a one‐carrier injection current. In neither material can the volume concentration of traps be determined from the voltage at which the current rises sharply.