Structure of A Power Diode

Power Diode

A power diode is a high power capability power semiconductor device used in power electronic circuits. A power diode is also a PN junction device and its functionality is similar to that of a normal low-power PN junction diode. But the construction of power diode is different from its counterpart and it is designed to carry high power.

Power Diode Structure

Structure of a power diode

In contrast to a normal PN junction diode which has only two layers P and N, a power diode contains three layers P+, N- and N+  as shown in the above figure. The symbol is same for both low power and high power diodes.

A power diode contains a lightly doped N- layer, epitaxially grown on a heavily doped N+ substrate. A heavily doped P+ layer is diffused in to the lightly doped N- layer. The N+ substrate forms the cathode and P+ layer forms the anode of the power diode.
The differentiating feature of the power diode with a low power signal diode is that the inclusion of N- layer in the power diode, which is absent in a signal diodes. Under reverse biased condition of the diode, this N- layer absorbs the depletion layer at P+,N- Junction. The breakdown voltages depends on the thickness of this region and it increases with increase in the thickness of the N- layer but this layer also adds higher ohmic losses to the diode under forward conduction. This results in high power and heat dissipation necessitating proper cooling requirements.

Also See:
Advantages of Power Electronics
Types of power electronic converters