First-principles study of the lattice integration of palladium defects in doped germanium and silicon

Time-differential perturbed angular correlations spectroscopy of palladium in doped germanium has identified palladium-vacancy pairing in n-type antimony-doped, p-type gallium-doped and undoped germanium. In contrast, an equivalent study of palladium defects in doped silicon suggests a different scenario for the silicon host. Palladium-vacancy pairing has been proposed in n-type silicon irrespective of the dopant type (phosphorous, arsenic or antimony) but palladium–boron pairing has been speculated to occur in p-type boron-doped silicon. This thus raises the question: why does palladium pair with a dopant atom in p-type silicon, but with a vacancy in p-type germanium? Based on the density functional theory calculations carried out in this work, it is suggested that the size of the dopant and the host material both play a crucial role in determining the type of palladium-defect complex that is formed. The calculations predict a configuration with the palladium atom on a bond-centered interstitial site pairing with a semi-vacancy on either side in gallium-doped and antimony-doped silicon and germanium, respectively. Whereas, a configuration with the palladium atom on a bond-centered interstitial site pairing with the dopant was proposed in boron-doped silicon and germanium. In further support of the argument, in n-type phosphorous-doped materials the calculations predict a configuration with the palladium atom on a bond-centered interstitial site pairing with a semi-vacancy on either side in silicon, but a configuration with the palladium atom on a bond-centered interstitial site pairing with the phosphorous dopant in germanium.