A Zener diode is a silicon semiconductor device that permits current to flow in either a forward or reverse direction. The Zener diode has a reverse-breakdown voltage, at which it starts conducting current, and continues operating continuously in the reverse-bias mode without getting damaged. The following two mechanisms can cause a breakdown in a junction diode:

(i) Avalanche breakdown

With increasing reverse bias voltage, the electric field across the junction of p-n diode increases. At a certain reverse bias, the electric field imparts a sufficiently high energy to a thermally generated carrier crossing the junction. This carrier disrupts a covalent bond and produces an electron-hole pair. This process is cumulative and produces an avalanche of carriers in a very short time. This mechanism is known as avalanche multiplication, causes large reverse current and the diode is said to work in the region of avalanche breakdown.

(ii) Zener breakdown

In a Zener diode, both the p and n-sides are heavily doped. Due to the high dopant densities, the depletion layer junction width is small. This high junction field may strip an electron from the valence band, which can tunnel to the n-side through the thin depletion layer. Such a mechanism of emission of electrons after applying a certain electric field is termed as internal field emission which gives rise to a high reverse current or breakdown voltage. This breakdown is termed as Zener breakdown.

To protect a diode from damage, we connect a protective resistance to a Zener diode which limits maximum current. Also, Zener diode is used as a voltage regulator.

Requirements for this Science Experiment

⦁ Zener Diode ⦁ Voltmeter ⦁ Milliammeter ⦁ Plug Key ⦁ Rheostat ⦁ Battery ⦁ Resistance