A model was presented which accounted for the anomalous diffusion of p-type dopants during the growth of bipolar transistors. The model was based upon Fermi-level pinning at the crystal surface during epitaxial growth. This led to an increased concentration of column-III interstitial defects in heavily n-type AlGaAs or GaAs. The excess column-III interstitials which were generated in the n-type crystal then flowed into the p+ base region and led to a transfer of p-type impurity atoms from column-III lattice sites to interstitial positions, via a kick-out mechanism. Once located in interstitial positions, the impurity atoms diffused rapidly. The model was consistent with previously proposed mechanisms for both impurity diffusion and column-III self-diffusion.

D.G.Deppe: Applied Physics Letters, 1990, 56[4], 370-2