In this work we show that the cooling rate following a platinum diffusion strongly influences the
electrical conductivity in weakly phosphorus doped silicon. Diffusions were performed at the
temperature of 910 °C in the range of 8–32 hours in 0.6, 30, and 60 Ω cm phosphorus doped silicon
samples. Spreading resistance profile analyses clearly show an n-type to p-type conversion under
the surface when samples are cooled slowly. On the other hand, a compensation of the phosphorus
donors can only be observed when samples are quenched. One Pt related acceptor deep level at 0.43 eV from the valence band is assumed to be at the origin of the type conversion mechanism. Its
concentration increases by lowering the applied cooling rate. A complex formation with fast species
such as interstitial Pt atoms or intrinsic point defects is expected. In 0.6 Ω cm phosphorus doped
silicon, no acceptor deep level in the lower band gap is detected by DLTS measurement. This
removes the opportunity of a pairing between phosphorus and platinum and suggests the possibility
of a Fermi level controlled complex formation.