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Ga depth distribution calculated from the results of RBS measurements for selected samples. There are no differences between the Ga profiles of the superconducting (sc) and the insulating (ins) sample. The notion for different depth regions used in the text is indicated.
Pseudocolor image of the silicon distribution in the cross section of the sample annealed at 600 °C for 60 s obtained from EFTEM. Ga accumulation and oxygen intermixing close to the interface lead to local Si depletion. The silicon concentration decreases from orange to blue. The multilayer structure is clearly mapped: glue, SiO2 layer, Ga rich nanolayer, and heavily doped Si with few impurity rich precipitates (from left to right).
Sheet resistance R□ as function of temperature for samples annealed at 650 °C at various annealing times. The inset shows the transition to the superconducting state in more detail. Zero residual resistance is observed for normal state resistances below 6 kΩ. The dashed lines are Arrhenius fits R = R0 exp(T0/T) with R0 = 865 Ω, 6944 Ω and T0 = 10.1 K, 5.8 K for the samples annealed at 75 s and 80 s, respectively.
The sheet resistance R□ measured at 10 K as function of annealing time for different annealing temperatures. The resistance gap between superconducting and insulating samples is indicated. There are two independent experimental series (I & II) for annealing at 650 °C. The lines are only to guide the eye.
Tentative sheet hole concentration p□ – sheet resistance R□ (@10 K) phase diagram of the superconductor-insulator transition. The separation of the phase regions is indicated (grey bars). In the vicinity of the transition point, the data of the 650 °C annealing follow a power law (solid line).
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