Arsenic incorporation and doping behaviour in silicon and SiGe epitaxial layers grovvn by gas source molecular beam epitaxy

Abstract

The incorporation of As into epitaxial Si and SiGe grown by gas source molecular beam epitaxy using disilane (Si2H6), germane (GeH4), and arsine (AsH3) as hydride sources has been investigated. Reflection high energy electron diffraction (RHEED) studies, secondary ion mass spectroscopy (SIMS) profiles, and electrochemical capacitance voltage (ECV) analyses were used to characterise As incorporation. The As isfound to show surface segregation with a Gibbs energy of segregation of 0·45 eV at 600°C in Si and 0·30 eV at 560°C in SiGe as determinedfrom RHEED intensity oscillation measurements of the growth rate variation on As saturated surfaces. Competing segregation between Ge and As in As doped SiGe causes an increase in the Ge concentration in the alloy of approximately 10% relative to that of the undoped alloy. Whereas the equilibrium As concentration attainable in Si is of the order of6 × 10 17 cm -3, it can reach values higher than 10 19 cm -3 in SiGefor equivalent partial pressure ratios ofAsH 3 to Si 2H 6 and/or GeH 4. For these concentration levels and growth conditions SIMS and ECV data indicate a unity activation ratio for As in these epitaxial films. © 1995 The Institute of Materials.