<P> The choice of the combination of the metal and semiconductor determines the forward voltage of the diode . Both n - and p - type semiconductors can develop Schottky barriers . However, the p - type typically has a much lower forward voltage . As the reverse leakage current increases dramatically with lowering the forward voltage, it cannot be too low, so the usually employed range is about 0.5--0.7 V, and p - type semiconductors are employed only rarely . 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 . </P> <P> With increased doping of the semiconductor, the width of the depletion region drops . Below a certain width, the charge carriers can tunnel through the depletion region . At very high doping levels, the junction does not behave as a rectifier anymore and becomes an ohmic contact . 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 . Lightly doped p - type regions pose a problem, as the resulting contact has too high a resistance for a good ohmic contact, but too low a forward voltage and too high a reverse leakage to make a good diode . </P> <P> As the edges of the Schottky contact are fairly sharp, a high electric field gradient occurs around them, which limits how large the reverse breakdown voltage threshold can be . Various strategies are used, from guard rings to overlaps of metallization to spread out the field gradient . The guard rings consume valuable die area and are used primarily for larger higher - voltage diodes, while overlapping metallization is employed primarily with smaller low - voltage diodes . </P> <P> Schottky diodes are often used as antisaturation clamps in Schottky transistors . Schottky diodes made from palladium silicide (PdSi) are excellent due to their lower forward voltage (which has to be lower than the forward voltage of the base - collector junction). The Schottky temperature coefficient is lower than the coefficient of the B--C junction, which limits the use of PdSi at higher temperatures . </P>

Why schottky diode is called hot carrier diode