Dopant diffusion and segregation in semiconductor heterostructures: Part 1. Zn and Be in III-V compound superlattices
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 (IIII2+), whose thermal equilibrium concentration, and hence also the diffusivity of Zn and Be, exhibit also a Fermi-level dependence, i.e., in proportion to p2. A heterojunction consists of a space-charge region with an electric field, in which the hole 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 IIII2+and of Zn- or Be-, which in turn influence the distribution of these ionized acceptor atoms. The process involves diffusion and segregation of holes, IIII2+, Zn-, or Be-, and an ionized interstitial acceptor species. The junction electric field also changes with time and position. © Springer-Verlag 1999.
Chen, CH; Gösele, UM; Tan, TY
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