The chemical interaction between high-concentration, mixed-ion-implanted group-III and -V impurities in silicon

Abstract

High-concentration, mixed group-III (In, Ga)/group-V (P,As) -implanted silicon single crystals have been studied by combining Rutherford backscattering spectroscopy/channeling spectrometry, Hall/resistivity measurements, transmission electron microscopy, and perturbed γγ angular correlation. A variety of processes and physical properties of the implanted layers are found to be dramatically changed in the mixed compared to the single implants. These include solid-phase recrystallization, redistribution of group-III and group-V atoms, phase nucleation and separation, lattice location of the impurity atoms, and electrical activation of the group-V atoms. The cause of these changes on a microscopic level is shown to be a strong chemical interaction between the donor and acceptor atoms, resulting in the formation of AIIIBV chemical compounds. For the As/In and P/In in Si systems, the formation of moleculelike AIIIBV complexes with donor and acceptor atoms sitting in substitutional silicon lattice sites is directly revealed by perturbed angular correlation measurements. A remarkable difference in the high-temperature annealing behavior is found between In- and Ga-doped, mixed implants: The precipitates found after high-temperature annealing in the In-doped samples are concluded to be mainly metallic particles whereas those found in the Ga-doped samples are AIIIBV compound precipitates coherent to the host lattice. The thermal stability of the AIIIBV compounds in silicon is suggested to be dependent on both the strength of the chemical bonds between the donor and acceptor atoms and the lattice mismatch between silicon and the crystalline phase of the AIIIBV compound.