Switching

The ability of diodes to conduct with forward bias, and to insulate with reverse bias, makes them useful for switching in some electronic applications. Diodes can switch at extremely high rates, much faster than any mechanical device.
One type of diode, made for use as an RF switch, has a special semiconductor layer sandwiched in between the P-type and N-type material. This layer, called an intrinsic semiconductor, reduces the capacitance of the diode, so that it can work at higher frequencies than an ordinary diode. The intrinsic material is sometimes called I type. A diode with I-type semiconductor is called a PIN diode (Fig. 1).

Fig. 1: The PIN diode has a layer of intrinsic (Itype) semiconductor at the P-N junction.

Direct-current bias, applied to one or more PIN diodes, allows RF currents to be effectively channeled without using complicated relays and cables. A PIN diode also makes a good RF detector, especially at frequencies above 30 MHz.