Diffusion and Defects in Elementary and Compound Semiconductors
Impact of doping and high dislocation densities on gold diffusion in silicon
Experiments on the diffusion of gold in undoped silicon are known to provide information about the contribution
of self-interstitials to silicon self-diffusion under intrinsic conditions. These former experiments demonstrate the
usefulness of gold as a probe atom for studying the properties of native defects in silicon. In order to investigate
the impact of high boron doping levels on gold diffusion, we performed diffusion experiments of gold in
homogeneously boron doped silicon single crystal. Silicon crystals with various boron doping levels grown by
the Czochralski (CZ) technique and highly dislocated samples were used for our diffusion experiments.
After diffusion the gold profiles were determined by means of the neutron activation analysis in conjunction
with serial sectioning and counting the specific activity of each section. Numerical analyses of the gold profiles
reveal that singly positively charged self-interstitials mainly mediate self-diffusion under p-type doping.
Moreover, the fast component of gold diffusion is found to be caused by singly positively charged interstitial
gold atoms. An enhanced boundary concentration and simultaneously retarded Au diffusivity was observed at
temperatures below 1000oC which provides direct evidence of Au segregation at dislocations. A
segregation enthalpy of 2.7 eV for the energy difference of Au atoms dissolved on substitutional lattice
sites and Au atoms trapped at dislocations was determined. The formation of spherical oxygen precipitates with
a diameter between 14 nm and 20 nm was detected with transmission electron microscopy in
CZ silicon samples. The precipitates cause an injection of self-interstitials in the silicon bulk and as a
consequence affects the diffusion behaviour of gold. The interference between precipitate formation and gold
diffusion provides information about the rate of oxygen precipitate formation and about the rate interstitial gold
is gettered at these microdefects.
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