The exponential rise in current with forward bias is described by Eq. (1.2) but with n
dependent on the construction technique (1.05 for the metal-whisker type of construction,
which is somewhat similar to the germanium diode). In the reverse-bias region, the
current I s is due primarily to those electrons in the metal passing into the semiconductor
material. One of the areas of continuing research on the Schottky diode centers on reducing
the high leakage currents that result with temperatures over 100°C. Through design,
improved units are available that have a temperature range from 65°C to 150°C. At
room temperature, I s is typically in the microampere range for low-power units and the
milliampere range for high-power devices, although it is typically larger than that encountered
using conventional p – n junction devices with the same current limits. In addition, the
PIV of Schottky diodes is usually significantly less than that of a comparable p – n junction
unit. Typically, for a 50-A unit, the PIV of the Schottky diode is typically 50 V or less as
compared to 150 V for the p – n junction variety. Recent advances, however, have resulted
in Schottky diodes with PIVs greater than 100 V at this current level. It is obvious from
the characteristics of Fig. 16.2 that the Schottky diode is closer to the ideal set of characteristics
than the point contact and has levels of V T less than those of the typical silicon
semiconductor p – n junction. The level of V T for the “hot-carrier” diode is controlled to a
large measure by the metal employed. There is a trade-off between temperature range and
level of V T . An increase in one appears to correspond to a resulting increase in the other.
In addition, the lower the range of allowable current levels, the lower is the value of V T .
For some low-level units, the value of V T can be assumed to be essentially zero on an approximate
basis. For the middle and high ranges, however, a value of 0.2 V appears to be
a good representative value.