Si interband tunnel diodes have been successfully fabricated by molecular beam epitaxy and room temperature peak-to-valley current ratios of 1.7 have been achieved. The diodes consist of opposing n- and p-type delta -doped injectors separated by an intrinsic Si spacer. A ''p-on-n'' configuration was achieved for the first time using a novel low temperature growth technique that exploits the strong surface segregation behavior of Sb, the n-type dopant, to produce sharp delta-doped profiles adjacent to the intrinsic Si spacer.