Cluster Model of Impurity States in Doped Semiconductors

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Abstract
We have performed a large scale pseudocluster calculation to investigate the density of states of impurity bands in doped semiconductors using an effective Hartree Hamiltonian. The pseudocluster consists of a core of N impurities surrounded by Ns impurities. The Hamiltonian matrix includes all the interactions between impurity ions and electrons. We discovered that some unreasonable results of other authors are due to the incomplete Hamiltonian matrix used. Three types of impurity states are found: Toyozawa atoms, impurity molecules and the extended states. These states play different roles for different physical properties. At the higher impurity concentrations, we found that it is very important to have the Ns surrounding impurities to overcome the cluster boundary effect.

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