Distribution of shallow dopants in semiconductor heterostructures in general exhibits a pronounced segregation phenomenon, which requires the description of the dopant atom diffusion and segregation processes simultaneously. We treat this class of problems in a series of three papers. In the present paper, which is the first of the three, Zn and Be distributions in III-V superlattice (SL) structures are discussed in detail. The analysis method developed in this paper is generally applicable to other cases. In the second paper we analyze B distribution in GeSi/Si heterostructures. In the third paper we treat the problems associated with a number of n-type dopants in a variety of semiconductor heterostructures. Segregation of a dopant species between two semiconductor heterostructure layers is explained by a model incorporating (i) a chemical effect on the neutral species; and (ii) a Fermi-level effect on the ionized species, because, in addition to the chemical effect,, the solubility of the species also has a dependence on the semiconductor Fermi-level position. For Zn and Be in GaAs and related compounds, their diffusion process is governed by the doubly-positively-charged group III element self-interstitials (I-III(2+)), whose thermal equilibrium concentration, and hence also the diffusivity of Zn and Be, exhibit also a Fermi-level dependence, i.e., in proportion to p(2). A heterojunction consists of a space-charge region with an electric field, in which the holt: concentration is different from those in the bulk of either of the two layers forming the junction. This local hole concentration influences the local concentrations of I-III(2+) and of Zn- or Be-, which in turn influence the distribution of these ionized acceptor atoms. The process involves diffusion and segregation of holes, I-III(2+), Zn-, or Be-, and an ionized interstitial acceptor species. The junction electric field also changes with time and position. [References: 16]

Full text :PDF (326 kB)( for personal use only)