system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it that semiconducting materials have lower resistances the hotter they get?
gpt
A material that conducts electricity well (a conductor) has lots of charged particles that can move around, allowing electrical current to flow. A material that doesn't conduct electricity (an insulator) has no movable charged particles (either there are no charged particles, or the charged particles are locked in place). A semiconductor is in between these two. There are some, but not many charged particles that can move around. One common way of having this condition is to have a medium-sized gap between the energy level of the highest energy electrons (in the ground state) and the lowest unoccupied energy level. If the gap is very small, then it's easy for electrons to jump up and move around, so you have a conductor. If the gap is very large, it's incredibly difficult for electrons to do so and you have an insulator. But with that medium gap, you have some-but-not-lots of electrons that can make the jump. Increasing the temperature increases the energy that the electrons have and therefore increases the fraction of electrons that can successfully make the jump up. With more electrons able to move around, electricity flows easier (resistance is lower).