The two-terminal magnetoresistance at base temperature (T≈50 mK) for aluminium and nickel silicide contact metallizations to the Si:P δ -layers. Figure 1a shows a small peak resulting from weak localization within the δ-layer, and can be fitted with the Hikami model as shown. Figure 1b shows the large resistance peak around B = 0 that results from the formation of the BCS energy gap in the superconducting aluminium contacts. The critical field B
= 10.5 mT for aluminium is shown, which coincides with the destruction of the resistance peak.