E0 is called the vacuum energy level, which symbolizes the surface energy level of the object. The Fermi level of a semiconductor is related to the doping concentration, so its work function is also closely related to the impurity concentration!

Metal:

semiconductor:

Metal:

semiconductor:

Wm>Ws: Electrons flow from semiconductor to metal, The surface energy brings bending, Form an electronic barrier, Form n-type barrier layer and p-type anti-blocking layer Wm<Ws: Electrons flow from metal to semiconductor, The surface energy band bends downward, Form a hole barrier, Form n-type anti-blocking layer, p-type blocking layer

Donor surface state: The surface below qΦ0 is electrically neutral when occupied by electrons, and becomes positive after releasing electrons.

Acceptor surface state: The surface above qΦ0 is electrically neutral when empty, and becomes negatively charged after accepting electrons.

Even if the surface state is not in contact with the metal, the surface will form a potential barrier. If the surface state density is very large, pinned occurs at high surface state density.

Without surface states, the work function of a semiconductor is:

There are surface states, and the work function of the semiconductor is:

V>0

V<0

The direction of change of the barrier height mainly depends on the moving direction of the carriers after applying the bias voltage. When electrons accumulate, the barrier height decreases.

For n-type barrier layers, when the width of the barrier is much larger than the mean free path of electrons, electrons will have to collide multiple times through the barrier area. This barrier is called a thick barrier; both drift and diffusion need to be considered

in conclusion:

When the n-type barrier layer is very thin, the electron mean free path is much larger than the barrier width. It is the barrier height that matters, not the barrier width.

in conclusion:

Cause Analysis:

Mirror force and tunnel effect have a significant impact on reverse characteristics 1) Causes the barrier height to decrease and increase the reverse current. 2) The greater the reverse voltage, the more significant the potential barrier decreases, and the greater the reverse current.

First, it depends on the concentration of minority carriers in the barrier layer. If the barrier is high enough, the concentration of holes close to the contact surface will be high. With an external voltage, the contribution of the minority carrier current will increase.

It also depends on the efficiency of hole diffusion into the semiconductor. The higher the diffusion efficiency, the greater the contribution of minority carriers to the current.

The forward current of the pn junction is the current formed by non-equilibrium minority carrier diffusion, which has a significant charge storage effect; the forward current of the Schottky barrier diode is mainly formed by the majority carriers of the semiconductor entering the metal. It is a multi-carrier device and has no accumulation. , so the high frequency characteristics are better;

The barrier area of ​​a Schottky barrier diode only exists on one side of the semiconductor

The forward conduction voltage of Schottky diodes is low, generally about 0.3V, and the pn junction is generally 0.7V.