Electrical Properties of Gold-related Defect Complexes in Silicon

Doktorsavhandling, 1994

This thesis describes three extensive experiments concerning the properties of gold as an impurity atom in crystalline silicon. The first study is an investigation of the effect of phosphorus diffusion on the distribution of gold atoms within a silicon crystal. It is demonstrated how gold atoms diffuse back and forth between the highly phosphorus-doped surface layer and the bulk of the material when the annealing temperature is varied. This is investigated using secondary ion mass spectroscopy (SIMS) to study the gold within the highly phosphorus-doped layer and using deep level transient spectroscopy (DLTS) to estimate the gold content in the bulk of the specimen. This phenomenon is related to large solubility enhancement of gold in silicon with phosphorus concentrations above approximately 3x1019 atoms/cm3. In the second study, hydrogen-gold complexes are investigated. Hydrogen is injected into the surface region of gold-doped samples during wet etching. From the results of annealing experiments we distinguish between three different configurations of hydrogen in relation to the substitutional gold atom. There is one position, S, where the electronic energy of the gold donor level is unaffected, a second position G, detected as three deep levels, and a third configuration, PA, where the gold center is apparently electrically inactive. The Au-H configurations transform into one another upon annealing. Heat treatment at temperatures above approximately 200oC results in an irreversible dissociation of the Au-H complexes and the gold centers are reactivated. The third experiment concerns the interaction between lithium and gold in n-type silicon. We find that lithium diffusion into gold-doped silicon results in passivation of gold acceptors. The passivation is attributed to a coulomb pair between Au- and Li+, with a free binding energy of approximately 0.87 eV. In addition, an electrically active Au-Li complex is observed consisting of one gold atom and one or more lithium atoms.