This can be used for the simultaneous formation of ohmic contacts and diodes, as a diode will form between the silicide and lightly doped n-type region, and an ohmic contact will form between the silicide and the heavily doped n- or p-type region. At very high doping levels, the junction does not behave as a rectifier any more and becomes an ohmic contact. Below a certain width, the charge carriers can tunnel through the depletion region.
With increased doping of the semiconductor, the width of the depletion region drops.
Titanium silicide and other refractory silicides, which are able to withstand the temperatures needed for source/drain annealing in CMOS processes, usually have too low a forward voltage to be useful, so processes using these silicides therefore usually do not offer Schottky diodes. As the reverse leakage current increases dramatically with lowering the forward voltage, it cannot be too low, so the usually employed range is about 0.15–0.45 V, and p-type semiconductors are employed only rarely. However, the p-type typically has a much lower forward voltage. Both n- and p-type semiconductors can develop Schottky barriers. The choice of the combination of the metal and semiconductor determines the forward voltage of the diode. This Schottky barrier results in both very fast switching and low forward voltage drop. The metal side acts as the anode, and n-type semiconductor acts as the cathode of the diode meaning conventional current can flow from the metal side to the semiconductor side, but not in the opposite direction.
Typical metals used are molybdenum, platinum, chromium or tungsten, and certain silicides (e.g., palladium silicide and platinum silicide), whereas the semiconductor would typically be n-type silicon. HP 5082-2800 Schottky Barrier Diodes for General Purpose ApplicationsĪ metal–semiconductor junction is formed between a metal and a semiconductor, creating a Schottky barrier (instead of a semiconductor–semiconductor junction as in conventional diodes).
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