Practice portal › Semiconductor Electronics › Intrinsic and Extrinsic Semiconductors
Asked in GUJCET 2007 · Doping and carrier concentration
Idea: a trivalent dopant such as boron, aluminium, gallium or indium has only three valence electrons, but in the silicon or germanium lattice it must join four neighbours.
One of those four covalent bonds is therefore left one electron short.
That empty place in the bond is the hole.
An electron from a neighbouring bond can step into it, which moves the vacancy the other way, so the hole drifts through the crystal like a positive charge.
So a hole is a missing electron in a covalent bond.
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