Tunneling devices in combination with transistors offer a way to extend the performance of existing technologies by increasing circuit speed and decreasing static power dissipation. We have investigated Si-based tunnel diodes grown using molecular beam epitaxy (MBE). The basic structure is a p(+) layer formed by B delta doping, an undoped spacer layer, and an n(+) layer formed by Sb delta doping. In the n-on-p configuration, low temperature epitaxy (300-370 degreesC) was used to minimize the effect of dopant segregation and diffusion. In the p-on-n configuration, a combination of growth temperatures from 320 to 550 degreesC was used to exploit the Sb segregation to obtain a low Sb concentration in the B-doped layer. Post-growth rapid thermal anneals for 1 min in the temperature interval between 600 and 825 degreesC were required to optimize the device characteristics. J(p), the peak current density, and the peak-to-valley current ratio (PVCR), were measured at room temperature. An n-on-p diode having a spacer layer composed of 4 nm Si0.6Ge0.4 bounded on either side by 1 nm Si, had a J(p)= 2.3 kA/cm(2) and PVCR = 2.05. A p-on-n tunnel diode with an 8 nm Si spacer (5 nm grown at 320 degreesC, 3 nm grown at 550 degreesC) had a J(p)= 2.6 kA/cm(2) and PVCR = 1.7.