Zener and Schottky Diodes

Forward bias is the term for current flowing through a diode in the direction indicated in the image above. The movement of holes and electrons in the diode can be viewed through the lens of moving electrons in the circuit. Electrons move in the opposite direction of current flow, from the negative to positive terminals of the battery. Electrons have a negative charge. As electrons flow from the negative terminal, they repel the free electrons in the n-doped side of the diode. Then, these free electrons attract the holes in the p-doped side, causing the diode to conduct the flow of electrons. The movement in of the holes and electrons in the diode can also be viewed from a current perspective, shown in the reverse bias section.

In alternating current applications, reverse bias occurs when current flows from the positive terminal of the battery to the n-doped side of the diode first. The free electrons in the n-doped semiconductor are attracted to the positive terminal, causing them to cluster on the right of the diode. Simultaneously, the holes in the p-doped side of the diode are attracted towards the negative terminal. This separation of the holes and the free electrons creates a large depletion zone in the middle of the diode. Due to this depletion zone, current does not flow through the diode during reverse bias.

• • High switching speed

  • Low junction capacitance

  • High-current density

  • Expensive

Applications

Schottky diodes are commonly used as power rectifiers in circuits. In this application, the diode prevents reverse bias when supplied an alternating current. This only allows current to flow through the circuit in the forward bias direction.

Solar panels use diodes in parallel with individual cells so shaded or broken cells can be bypassed. Schottky diodes are preferred because the the low turn on voltage requires a lower percentage of the energy produced.

Radio frequency mixers also use Schottky diodes because of the high switching speed required.