Variable-Temperature I–V: Reading the Carriers

An electrical stage lands probes on the sample and sweeps current versus voltage at a set temperature. The slope is the conductance — and which way it moves with temperature tells you what kind of conductor you have.

25 °C
Interactive current-voltage plot measured through two probes on a sample. For a semiconductor the I-V slope steepens as temperature rises because more carriers are thermally generated, so resistance falls; for a metal the slope shallows as temperature rises because phonon scattering grows, so resistance rises.
Temperature
25 °C
Resistance (rel.)
1.00
Trend dR/dT
negative
The physics. In a semiconductor the carrier density rises as n ∝ exp(−Eg/2kT), so conductance climbs steeply with temperature and resistance falls. In a metal the carriers are already there; heating just adds lattice vibrations that scatter them, so resistance rises roughly linearly. The opposite signs of dR/dT are a direct readout of the conduction mechanism.