Electrical characterization of an ultrahigh concentration boron delta-doping layer

We report a boron δ-doping layer in crystalline silicon with an electrically active concentration of 1×1022 cm−3 and a mobility of ∼20 cm2/V s. This structure was fabricated by low-temperature molecular-beam epitaxy with boron confined to 3 monolayers in the silicon growth direction. Complete electrical activation is observed, showing metallic conduction down to 4 K. This two-dimensional doped layer, incorporated into the crystal lattice, represents a volume concentration exceeding the solid solubility of boron in silicon by two orders of magnitude. These high-concentration structures fill an unexplored region of the mobility versus concentration curve.