Papers Published

1. Chang-Ho Chen and Gosele, U.M. and Tan, T.Y., Fermi-level effect and junction carrier concentration effect on p-type dopant distribution in III-V compound superlattices, III-V and IV-IV Materials and Processing Challenges for Highly Integrated Microelectronics and Optoelectronics. Symposium (1999), pp. 219 - 24 .
   (last updated on 2007/04/10)

   Abstract:
   The pronounced segregation phenomenon in the distribution of p-type dopants Zn and Be in GaAs and related III-V compound heterostructures has been explained quantitatively by treating simultaneously the processes of dopant atom diffusion, segregation, and the effect of heterojunction carrier concentrations on these two aspects. Segregation of a dopant species between two semiconductor heterostructure layers is described by a model incorporating (i) a chemical effect on the neutral species; and (ii) in addition, a Fermi-level effect on the ionized species. The process of Zn and Be diffusion in GaAs and related compounds is governed by the doubly-positively-charged group III element self-interstitials I_III²⁺ whose thermal equilibrium concentration and hence also the Zn and Be diffusivities exhibit also a Fermi-level dependence, i.e., in proportion to p². A heterojunction is consisting of a space charge region with an electric field, in which the hole concentration is different from those in the bulk layers. This influences the junction region concentrations of 1_III²⁺ and of Zn^- or Be^-, which in turn influence the distribution of the ionized acceptor atoms. The overall process involves diffusion and segregation of holes, I_III²⁺, Zn^- or Be^-, and an ionized interstitial acceptor species. The junction electric field also changes with time and position

   Keywords:
   beryllium;carrier density;diffusion;doping profiles;Fermi level;gallium arsenide;III-V semiconductors;impurity states;interface states;segregation;semiconductor heterojunctions;surface diffusion;zinc;