If carriers can be holes or free electrons, why isn´t the intrinsic carrier concentration equal to the sum of the free electron concentration and the hole concentration in the semiconductor?
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\$\begingroup\$ Something to think about: What happens if you have holes (un-filled electron states) and free electrons in the same area of a semiconductor? \$\endgroup\$– asdfexCommented Jun 28, 2022 at 13:41
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\$\begingroup\$ Aren´t holes and electrons in diffrent bands? \$\endgroup\$– denizyildiz70Commented Jun 28, 2022 at 13:42
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\$\begingroup\$ "Bands" - yes. But these are not kind of separate. Bands are just different energy levels. And nothing prevents an electron from radiating some of its energy and dropping into a hole. \$\endgroup\$– asdfexCommented Jun 28, 2022 at 14:40
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I dont get what you mean .In semiconductors the conductivity of the semiconductor $$\sigma$$ is equal to:
$$\sigma = en_{e}\mu _{De}+en_{h}\mu _{Dh}$$
we take into account both the drift of electrons and holes
