Following section explains the rectifying contacts in brief & also derives it.
- When a forward-bias voltage V is applied to the Schottky barrier of Fig.b, the contact potential is reduced from V0 to V0 - V (Fig.a).
- As a result, electrons in the semiconductor conduction band can diffuse across the depletion region to the metal.
- This gives rise to a forward current (metal to semiconductor) through the junction.
- Conversely, a reverse bias increases the barrier to V0 Vr, and electron flow from semiconductor to metal becomes negligible.
- In either case flow of electrons from the metal to the semiconductor is retarded by the barrier Φm - x.
- The resulting diode equation is similar in form to that of the p-n junction
as Fig. c suggests. In this case the reverse saturation current I0 is not simply derived as it was for the p-n junction.
- One important feature we can predict intuitively, however, is that the saturation current should depend upon the size of the barrier ΦB for electron injection from the metal into the semiconductor.
- This barrier (which is Φm - x for the ideal case shown in Fig.) is unaffected by the bias voltage.
- We expect the probability of an electron in the metal surmounting this barrier to be given by a Boltzmann factor. Thus
- In both of these cases the Schottky barrier diode is rectifying, with easy current flow in the forward direction and little current in the reverse direction.
- We also note that the forward current in each case is due to the injection of majority carriers from the semiconductor into the metal.
- The absence of minority mcarrier injection and the associated storage delay time is an important feature of Schottky barrier diodes.
- Although some minority carrier injection occurs at high current levels, these are essentially majority carrier devices.
- Their high-frequency properties and switching speed are therefore generally better than typical p-n junctions.