Boron delta doping in Si and Si0.8Ge0.2 layers

By using an elemental boron effusion cell, B delta doping structures (5×1013 B atoms/cm2) were grown on Si (100) by molecular beam epitaxy at different substrate temperatures and cap layer compositions (Si and Si0.8Ge0.2). Close to the delta interface the B profiles are characterized by an exponential decay in growth direction. For the Si cap the results suggest the existence of a transition from equilibrium segregation (exponential decay length ≂20 nm) to kinetically limited segregation (transition temperature ≂600 °C at 0.1 nm/s). The doping profiles also give evidence of a temporal change of the segregation coefficient which is probably caused by clustering of segregating B atoms.