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This video seems to confuse semiconductors with "materials with a negative thermal coefficient of resistivity". Saying "this gets more conductive as you heat it

This video seems to confuse semiconductors with "materials with a negative thermal coefficient of resistivity". Saying "this gets more conductive as you heat it up" does not a semiconductor make, as far as I understand.

brendank310 4y ago
Why not? It's not practical for traditional uses of semiconductors, but it has a mechanism to control conductivity.
- melony 4y ago
  Put it in a bell jar and pump the air out. Violà, vacuum tube.
- ilyt 4y ago
  Because then you'd need to call resistors "semiconductors" coz they also change resistance with temperature and that's not useful to anyone.
  - adrian_b 4y ago
    In any normal resistor, which is made from a conductive material, the resistance increases with the temperature, because the "friction" between the electricity carriers and the atomic lattice increases. Only in resistors made of semiconductors, i.e. in NTC thermistors, the resistance decreases with the temperature. The difference between a conductor and a semiconductor is that in the former the concentration of the carriers is constant, while in the latter the concentration of the carriers can be changed by various means, e.g. by temperature, by light, by impurities, by corpuscular radiation, by electrical fields, by contact with other materials, and by other means. In most intrinsic semiconductors, the carrier concentration increases with the temperature, therefore the resistance decreases with the temperature. This is a valid method to determine that a material is a semiconductor, even if false negatives are possible, when a material is a semiconductor though its resistance increases with the temperature.
kragen 4y ago
it's true that conventional insulators also have a negative tc but as i understand it that's because they're just really cold semiconductors
adrian_b 4y ago
Any material that "gets more conductive as you heat it up" is a semiconductor, unless its conductivity remains negligible, in which case it is an insulator. Not all semiconductors "get more conductive as you heat them up". A counterexample is provided by heavily doped semiconductors.

brendank310 4y ago

Why not? It's not practical for traditional uses of semiconductors, but it has a mechanism to control conductivity.

melony 4y ago
Put it in a bell jar and pump the air out. Violà, vacuum tube.
ilyt 4y ago
Because then you'd need to call resistors "semiconductors" coz they also change resistance with temperature and that's not useful to anyone.
- adrian_b 4y ago
  In any normal resistor, which is made from a conductive material, the resistance increases with the temperature, because the "friction" between the electricity carriers and the atomic lattice increases. Only in resistors made of semiconductors, i.e. in NTC thermistors, the resistance decreases with the temperature. The difference between a conductor and a semiconductor is that in the former the concentration of the carriers is constant, while in the latter the concentration of the carriers can be changed by various means, e.g. by temperature, by light, by impurities, by corpuscular radiation, by electrical fields, by contact with other materials, and by other means. In most intrinsic semiconductors, the carrier concentration increases with the temperature, therefore the resistance decreases with the temperature. This is a valid method to determine that a material is a semiconductor, even if false negatives are possible, when a material is a semiconductor though its resistance increases with the temperature.

kragen 4y ago

it's true that conventional insulators also have a negative tc but as i understand it that's because they're just really cold semiconductors

adrian_b 4y ago

Any material that "gets more conductive as you heat it up" is a semiconductor, unless its conductivity remains negligible, in which case it is an insulator. Not all semiconductors "get more conductive as you heat them up". A counterexample is provided by heavily doped semiconductors.