A Back diode or Backward diode is a tunnel diode that has better conduction for small reverse biases (typically –0.1 to –0.6 V) than for forward bias voltages.
Compared to a typical tunnel diode, one side of the junction is less heavily doped than the other, leading to a reduced effect of tunneling in the forward direction (a much less prominent negative resistance area). In the reverse direction, there is strong conduction at very low voltages already.
Among other purposes, it can be used as a rectifier for small signals, and will work at very high frequencies (50+ GHz) due to the absence of charge storage. When used as a rectifier, the reverse direction is used to conduct, whereas the forward direction blocks current flow for small signals (see diagram). This use which is "backward" from how a normal diode would rectify a signal has given the back diode its name.
Examples of back diodes include:
- Backward diode @ Wikipedia
- Backward diode @ electronics-notes.com
- Tunnel diode switching circuits and the back diode. Service Scope No. 38, June 1966 and No. 39, August 1966
- Russian back diodes