The general Green's-function solutions for the two carrier concentrations under any small signal nonuniform carrier generation

Thus far the general theory of the spatial distribution of photocarriers under the presence of a small signal inhomogeneous photocarrier generation has been limited to the one carrier case. In this work the more general and more complicated case of the spatial distribution of the two types of excess carriers is addressed. This distribution is pertinent in particular to the newly developed photocarrier grating (PCG) technique. The above two carrier problem and the PCG technique are discussed in a much broader context than previously given in the literature. A Green's-function approach, applied here for the first time, provides a general recipe for the problem of inhomogeneous carrier generation and it gives a better physical insight into the corresponding system by showing how the local carrier concentration is determined by the carrier generation in the entire sample. Hence the mathematical and physical basis for the PCG technique is provided here. The generality and the usefulness of the present approach for the nontrivial carrier generations of the "single square pulse," the "square wave,"and the "one period sinusoidal pulse," which have not been considered previously, are demonstrated.