Interface trapping in unipolar space-charge-limited current

It is assumed almost invariably in the literature that traps, when present, are distributed uniformly in the bulk of a device. But in unipolar space-charge-limited current (sclc) charge carrier traps suppress current most efficiently when located in the immediate vicinity of the emitter. A new model is developed, therefore, which accounts for this result by assuming that the traps responsible for the current suppression are located at the emitter interface in a surface concentration Σ while the bulk remains free of traps. The analysis has been carried out for traps with one discrete trapping level Etbelow the edge Ebof the conducting band and for the five distinct cases of planar, cylindrical, and spherical configuration. The main results are: (a) The V-I characteristic exhibits the VTFLtypical to many experimental results. (b) The relevant parameter is the ratio , where r is a length characteristic of the geometrical configuration of the device and N is the effective density of states of the conducting band. (c) For a semispherical emitter ("point contact") unipolar sclc dominated by interface trapping is essentially independent on sample dimensions.