Question

Distinguish between Avalanche breakdown and Zener breakdown.

Answer 1

Hint in these types of questions we have to give definition of given physical terms and we have to give facts that can differentiate them from each other. So firstly we will give the facts of Zener breakdown and at the last we will explain the avalanche breakdown.

Complete Step by step solution
Zener breakdown: this process occurs in heavily doped junction diodes.in these types of diode both p- and n- sides are doped by the acceptor and donor impurities respectively. Due to high dopant density, the width of the junction layer is small and the barrier field ($E = V/d$) is high.
When a large reverse bias is applied across such a diode the depletion layer and the energy bands get modified. As the depletion width is very small ($< {10^{ - 7}}m$), even a small voltage(say 4V) will set up a high electric field of $4 \times {10^7}V{m^{ - 1}}$. This high electric field strips off many electrons from the valence band which tunnel to the n-side through the thin depletion layer. This method of emission of electrons beyond a certain reverse bias voltage ${V_Z}$is called internal field emission. It gives rise to a large reverse current or breakdown current . This breakdown in a diode due to the band-to -band tunneling is called Zener breakdown and such diode is called Zener diode.
Avalanche breakdown: This process occurs in the diode having low level of doping and hence wide depletion layer. When the reverse bias voltage is sufficiently high, the minority charge carriers get highly accelerated. Their kinetic energy becomes high enough and they knock-off electrons from covalent bonds of the semiconductor. The newly generated electron-hole pairs also get accelerated and cause ionization. Thus a chain of collisions is set up which gives rise to a very large number of charge carriers. This leads to a large reverse current . This phenomenon is called Avalanche breakdown and the device is called avalanche diode.

Note
Both devices Zener diode and avalanche diode work in the reverse bias voltage.
Avalanche is due to the low doping and Zener breakdown in the high doping.