Pure silicon is very nearly an insulator; it only becomes the stuff of every chip once it is deliberately contaminated with a sprinkling of foreign atoms. The heavier the doping the denser the carriers, and the kind of dopant decides whether the majority carriers are electrons in n-type material or holes in p-type. Joined together, the two make a diode: the I–V characteristic rises steeply at a knee near 0.7 V under forward bias, while under reverse bias almost no current passes at all. At that same junction, a voltage on the gate builds the MOSFET channel, an electrical valve opened and closed by voltage alone.
Pure silicon is very nearly an insulator; it only becomes the stuff of every chip once it is deliberately contaminated with a sprinkling of foreign atoms. The heavier the doping the denser the carriers, and the kind of dopant decides whether the majority carriers are electrons in n-type material or holes in p-type. Joined together, the two make a diode: the I–V characteristic rises steeply at a knee near 0.7 V under forward bias, while under reverse bias almost no current passes at all. At that same junction, a voltage on the gate builds the MOSFET channel, an electrical valve opened and closed by voltage alone.
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