Simple analysis and computer simulation on lateral spreading of space charge in bulk GaAs

The growth of a space charge in bulk GaAs with a uniform doping profile but with a highly and three-dimensionally non-uniform electric field has been analyzed by introducing a concept of a "carrier current tube." From this analysis it has been shown how the behavior (i.e., growth or decay) of a small space charge depends upon the magnitude of an initial space charge, the nonuniformity of the field, and the dielectric relaxation time and that a space charge grows where the electric field changes along the carrier current even if no initial space charge exists. The "lateral spreading velocity" of a dipole domain has been estimated (its value is the order of 10⁸cm/s) and its dependence upon the magnitude of an initial domain has been made clear. Furthermore, computer simulation have been performed for bulk GaAs devices with two-dimensional structure, such as a planar electrode, a nonuniform doping profile, and an imperfect cathode notch. The process of two-dimensional dipole domain formation in these devices has been made clear.