Semiconductor Diodes

60 SEMICONDUCTOR DIODES by T. Wigmore Although many readers know perfectly well what a diode is, it does no harm to repeat its definition here: it is any electronic device that has only two electrodes. There are two types of diode: thermionic and semiconduc- tor. The present article will discuss semiconductor types only. A semiconductor diode is basically a p-n junction, that is, a junction of n-type and p-type semiconductor material, currently usually silicon. An ideal junction of this nature, forgetting for the moment special types, such as zener diodes and varactors, behaves either as a short-circuit or as an infinite resistance, depending on the pola- rity of the applied voltage. Such a diode would possess differential resistance, rd, and d.c. resistance, Rd, only. Unfortuna- tely, ideal components do not exist and in a practical diode other parameters, such as bulk resistance, Rb; junction capacitance, the other parameters in Fig. I may be region. ignored. C.. diffusion cap...