Rectifying Contacts - Derivation

Introduction: This section gives brief explanation about the rectifying contacts with derivation:

Rectifying Contacts:

• When we apply a forward bias voltage V to the Schottky barrier shown in fig. b, the contact potential is decreased from V0 to V0-V(fig. a).
• As a result, electrons in the semi conduction band can diffuse across the depletion region to the metal.
• This help in producing the forward current (metal to semiconductor) through the junction.
• Conversely, the barrier is increased to V0 +Vr by the reverse bias, and there is negligible flow of electron from semiconductor to metal.
• In any of the case, electron flow from the metal to the semiconductor is slow down by the barrier Fm - x.
•  The resultant equation of diode is equivalent to that of p-n junction.

as suggested by figure c. Here, the reverse saturation current I0 is not derived simply as it was done in the case of p-n junction.

• One crucial feature which can be predicted intuitively, however, is that the saturation current should be dependent on the barrier size FB for injection of electron from the metal in the semiconductors.
• This barrier (for ideal case it is Fm - x as represented in fig.) is not affected by the bias voltage.
• We expect that we can find the probability of an electron which is surmounting this barrier with the help of Boltzmann factor. Therefore,

• In both cases, the Schottky barrier diode is rectifying, with small current in the reverse direction and easy flow of current in the forward direction.
• It is also noted that in each case the forward current is due to majority carriers injection from the semiconductor in the metal.
• The absence of injection of minority carriers and the related delay in storage is a notable feature of  Schottky barrier diodes.
• However some minority carrier injections occurring at high levels of current, these are essentially majority carrier devices.
• Their switching speed and properties related to high-frequency are thus better than usual p-n junctions generally.