In semiconductor devices, a backward diode (also called back diode) is a variation on a Zener diode or tunnel diode having a better conduction for small reverse biases (for example –0.1 to –0.6 V) than for forward bias voltages.
The reverse current in such a diode is by tunneling, which is also known as the tunnel effect.
Read more about Backward Diode: Current–voltage Characteristics of Backward Diode