Schottky Diode

SCHOTTKY DIODE

Principle

Schottky diode is a unilateral device, in which current flows form metal to semiconductor (n-type) in one direction.

Symbol:

The symbol of a schottky diode is as shown in Fig. 2.34.

Construction

A schottky diode also called as schottky barrier diode (or) hot carrier diode is formed by metals such as chromium, Aluminium molybdenum, platinum, gold, etc and an n-type semiconductor (silicon).

A schottky barrier diode is made up of 2 junctions, viz.

1. A unilateral metal-semiconductor junction.

2. A bilateral metal-semiconductor junction, as shown in Fig. 2.35

Here, the schottky diode act as a terminal device in which metal (1) and the semiconductor, formed at one end act as a Anode with unilateral junction and metal (2) and the semiconductor formed at the other end act as cathode with bilateral junction.

At the ohmic contact, the potential barrier is almost zero. The built in potential of the diode is a function of temperature and doping i.e., The potential decreases with the increase in temperature (or) doping of the semiconductor.

Working

The diode is forward biased. The voltage applied to the diode, is slowly increased in steps of 0.1V, 0.2V etc and the current is measured. The V-I characteristics curve of the schottky diode is as shown in Fig. 2.36 along with the V-I characteristics curve for a pn junction diode for comparison.

From Fig. 2.36 we can see that the forward voltage drop [0.3V] is very less, when compared to p-n junction diode the forward voltage drop [0.7V] and hence for a schottky diode the current increases enormously even for a small applied voltage. The current in the schottky diode is due to 3 components viz.,

(i) Diffusion current (I_D)

(ii) Tunnelling current (I_T)

and (iii) Thermoionic emission current (I_TE)

Total current I_Total = I_D+I_T+ I_TE

Applications

(i) As the schottky barrier diodes have very low voltage drop, they are used in high switching system efficiency component.

(ii) They are used in Bipolar Junction Transistor (BJT).

(iii) They are also used in voltage clamping and voltage rectifying applications.

(iv) Schottky diodes play a vital role in GaAs circuits and high power applications.