P-Type Surface Layers in Ion-Bombarded Silicon

Abstract

Silicon is bombarded at 400° to 900°C in a glow discharge of hydrogen with phosphine or diborane admixtures. Below 700°C, bombardment of n-type silicon with an initial resistivity of 200 Ω-cm creates deep (0.5–2.5μ) p-type surface layers regardless of gas composition. The concentration NA(x) of the acceptors in the p layers obeys a simple law: NA(x)=N0 exp(−x/L). N0 is the surface concentration at x=0 which increases from 3.5×1016 acceptors cm−3 to 4×1018 acceptors cm−3 for bombardment temperatures increasing from 500° to 650°C. The decay constant L is found to be 0.2 μ. Annealing experiments rule out the hypothesis that the p layers are caused by fast-diffusing acceptor impurities, e.g. aluminum or boron. It is proposed that the p layers are formed by vacancies which act as acceptor-like defects.