Schottky diodes

Schottky diodes are constructed of a metal-to-N junction rather than a P-N semiconductor junction. Also known as hot-carrier diodes, Schottky diodes are characterized by fast switching times (low reverse-recovery time), low forward voltage drop (typically 0.25 to 0.4 volts for a metal-silicon junction), and low junction capacitance. The schematic symbol for a Schottky diode is shown at the right.

In terms of forward voltage drop (V_F), reverse-recovery time (t_rr), and junction capacitance (C_J), Schottky diodes are closer to ideal than the average "rectifying" diode. This makes them well suited for high-frequency applications. Unfortunately, though, Schottky diodes typically have lower forward current (I_F) and reverse voltage (V_RRM and V_DC) ratings than rectifying diodes and are thus unsuitable for applications involving substantial amounts of power.

Schottky diode technology finds broad application in high-speed computer circuits, where the fast switching time equates to high speed capability, and the low forward voltage drop equates to less power dissipation when conducting.

The following illustration shows the structure of a Schottky diode. The metal semiconductor contact made of molybdenum/silicon represents the barrier. In the junction region between insulator, metal and semiconductor, a degradation of the barrier arises as a result of an abrupt change in the surface states. There, substantially higher reverse and forward currents would flow, which could impair the reliability of the diode. A complementarily doped guard ring on the semiconductor fixes this, concentrating the current through the diode on the actual diode region by increasing the barrier.

A typical cross section of a Schottky diode with the LP (low pressure) nitride passivation.

At the outside edge, a channel stop with an attached n-region and a connection to the back serves to further isolate the channel.