p-type doping by platinum diffusion in low phosphorus doped silicon

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 910degreesC in the range of 8 - 32 hours in 0.6, 30, and 60 Omega cm phosphorus doped silicon samples. Spreading resistance pro. le 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 Omega 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.