Silicon-Based Tunnel Diode Technology

Tunnel diodes have received interest because of their remarkable multivalued I-V characteristic and inherent high switching speeds. The exploration of tunnel diode applications was impeded by the incompatibility of tunnel diode fabrication technology with integrated-circuit processing. Rapid thermal diffusion from spin-on diffusants is the particular focus of this work as a basis for establishing a rapid thermal processing method compatible with commercial foundry processes. Vertical tunnel diodes formed on high resistivity substrates have been demonstrated to allow S-parameter measurements and extraction of a full ac device model. A current density of 2.7 Ì_å_A/Ì_å_m2 and peak-to-valley current ratio (PVR) of 2.25 has been achieved, which is the best result ever achieved using spin-on diffusants. Several other approaches were also explored such as flash-lamp annealing and rapid thermal annealing from doped metal sources. Phosphorus activation was improved using flash-lamp annealing. Tunnel diodes were formed by rapid thermal annealing from an Al:B:Si source on Si with a peak current density of 2.7 Ì_å_A/Ì_å_m2. Backward diodes were formed by evaporating 50 and 100 nm undoped Ge layer as well as 100 nm Al on an n+ Ge. This indicates that the undoped amorphous Ge was successfully transformed into heavily doped crystalline Ge. Transmission Electron Microscopy (TEM) was taken which allow characterization of the regrown layer thickness. TEM also showed that the regrown layer is clearly epitaxial and free of defects. The potential and limitations of each approach is discussed in this work.