n-type semiconductor
/ EN-type SEM-ee-kun-DUK-ter /
Imagine a quiet room where almost nobody moves, and then you let in a small group of restless people who pace around freely. Those few movers do all the running about. An n-type semiconductor is like that room: a crystal in which a population of free electrons does nearly all the work of carrying current.
You make an n-type semiconductor by doping a pure crystal with donor atoms — impurities that each release one extra, loosely held electron into the conduction band. The result is a material with far more free electrons than holes. Because the electrons hugely outnumber the holes, electrons are the majority carriers and holes the minority. The 'n' stands for negative, the sign of the electron's charge.
n-type material is one of the two essential ingredients of nearly every semiconductor device; joining it to p-type material creates the junctions that make diodes, transistors, and solar cells work. A point worth stressing: 'n-type' does not mean the material is negatively charged. The added donors leave behind fixed positive ions that exactly balance the extra electrons, so the crystal as a whole stays neutral.
Silicon doped with phosphorus is the textbook n-type material. Each phosphorus atom contributes one free electron, so a piece of phosphorus-doped silicon conducts mainly through those electrons streaming through the conduction band.
Phosphorus-doped silicon: electrons are the majority carriers.
Even n-type material still has a few holes, created by ordinary thermal excitation; they are simply vastly outnumbered. Those minority holes are not irrelevant — in transistors and solar cells the behavior of minority carriers can be decisive.