Constraining the absolute 3D dopant density in aluminum delta layers

Using four unique measurement techniques, we report the saturation 2D dopant density of 2.8(5) x 10¹⁴  atoms/cm² for aluminum on the silicon (Si(100)) surface, the effective carrier activation, and the emergence of a second, high mobility conduction band above ~30 K — outcomes of an effort to achieve an Al doped superconducting phase in Si. Scanning tunneling microscopy (STM) is used to directly measure dopants on the Si(100) surface before solid phase epitaxial growth of the Si capping layer. Subsequent secondary ion mass spectrometry (SIMS) and atom probe tomography (APT) are used to separately measure the number and distribution of dopants, while Hall transport measurements are used to measure carrier density at various temperatures. At this time, we believe a density of ~6 x 10²⁰ atoms/cm³ (~1.2 at %) was reached, but no evidence of superconductivity has been observed.