Hot Carrier Diode (HCD)

The hot carrier diode (HCD) is formed by placing an N-type semiconductor material (usually silicon) in contact with a metal such as gold, silver or aluminium to form a metal-to-semiconductor junction. This diode operates in a manner similar to ordinary PN junction diodes but there are several important differences. The barrier voltage developed within the device is approximately one half as great as the barrier voltage within an ordinary silicon diode. This means that the forward voltage drop across the diode is approximately 0.3 volts instead of 0.6 or 0.7 volts. Also, the HCD operates with majority carriers (electrons); virtually no minority carriers are involved. This means that the reverse or leakage current through the device is extremely small.

 The term hot carrier diode is used because the electrons move from the N-type semiconductor material cathode across the junction to the metallic anode (the forward-biased direction of current flow) in a manner similar to the movement of electrons through a vacuum tube diode.  In other words the electrons possess a high level of kinetic energy just like the electrons leaving the heated cathode of a vacuum tube.

The barrier voltage produced within the HCD is often referred to as the Schottky-barrier because the German scientist Schottky discovered the operating principle of the device in 1938.  For this reason the HCD is also commonly referred to as a Schottky-barrier diode or simply a Schottky-diode.

The HCD is able to change operating states (turn on and off) much faster than ordinary PN junction diodes, and it is used extensively to process high frequency AC signals.  This device finds extensive use in microwave electronic mixers (circuits which combine AC signals), detectors (circuits which use rectification as a means of extracting information from AC signals) , and high speed digital logic circuits