Discussion
Which one of the following statements is true for an intrinsic semiconductor?
Answer: A
The statement taken as true is that electrical conductivity increases with increasing temperature and pressure.
In an intrinsic semiconductor the carriers are thermally excited across the band gap, and their concentration varies as \(\exp(-E_{g}/2kT)\). Raising the temperature therefore increases the conductivity sharply, which rules out both options with decreasing temperature.
For pressure, the paper follows the textbook picture in which compressing the lattice increases the overlap of atomic orbitals, broadens the bands and narrows the gap, so more carriers are excited (silicon behaves this way; some semiconductors, such as germanium, show the opposite trend). On that picture conductivity rises with pressure, which rules out 'decreasing pressure'.
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