# How do transistors work, anyway?
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In most materials, valence electrons are tightly bound to the substrate, and a considerable energy is needed to knock them out; that energy is often sufficient to set things on fire along the way. This situation is different in metals, where some electrons at their normal energy levels can freely drift from one atom to another — forming what’s known as the electron gas.
Pure semiconductors have poor electrical properties, but their conductivity improves significantly in the presence of impurities known as dopants. An n-type dopant, such as phosphorus, adds mobile electrons to the semiconductor substrate, in effect increasing the number of charge carriers available at any given time. A p-type dopant, such as boron, does the opposite — trapping other electrons and thus creating long-lived valence shell vacancies (“holes”) in the base material. Interestingly, the slack afforded by these holes means that the distribution of non-excited valence electrons can all of sudden shift with ease in response to external electric fields. You can think of this as electrons opportunistically slithering into nearby vacancies, or you can look at holes as weird disembodied “particles” that drift in the opposite direction in a sea of valence electrons. However you approach it, both n-type and p-type materials conduct much better than pure silicon.
It should be noted that doped semiconductors remain electrically neutral. Only the mobility of electrons is changing, not the ratio of electrons to protons in the crystal lattice.