ELECTRICAL CHARACTERIZATION OF AN ULTRAHIGH CONCENTRATION BORON DELTA-DOPING LAYER

We report a boron delta-doping layer ia crystalline silicon with an electrically active concentration of 1 x 10(22) cm-3 and a mobility of approximately 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.