Asked by: satya Subject: semiconductor Question: what is the reason for negative temperature coefficiant in semiconductors -- Visitor Ip: 117.195.234.169

A negative temperature coefficient (NTC) occurs when the thermal conductivity of a material rises with increasing temperature, typically in a defined temperature range. For most materials, the thermal conductivity will decrease with increasing temperature.

Negative temperature coefficient (NTC) is a common feature of semiconductors, because the number of charge carriers increases strongly with temperature. In metals, conversely, the number of charge carriers isn't strongly dependent with temperature. Instead, the dominating effect is increased carrier scattering with temperature. This results in a positive temperature coefficient of resistance: increased resistance due to a temperature increase.

NTC means the sign of dR/dT in R-T graph of a typical SC is negative, As w 9 that SC means they have a energy band gap between CB and VB (say Si~1.1 eV), so electron required an energy to cross over this band gap, the required energy we can provide by many ways say LIGHT, HEAT etc. Now we 9 that in non-degenerate SC electrons having Boltzmann energy distribution (http://www.gs68.de/tutorials/plasma/node7.html), and when we increase the temperature, then energy Maxim shifted towards higher energy, hence the number of electron having energy greater then the band gap increases, as a result more electron reaches in CB and participate in conduction , as a result conductivity increases or resistance decreases. In case of metal R increases as we increases the TEMP. due to electron - electron, and electron-phonon collisions.

A negative temperature coefficient (NTC) occurs when the thermal conductivity of a material rises with increasing temperature, typically in a defined temperature range. For most materials, the thermal conductivity will decrease with increasing temperature.

Negative temperature coefficient (NTC) is a common feature of semiconductors, because the number of charge carriers increases strongly with temperature. In metals, conversely, the number of charge carriers isn't strongly dependent with temperature. Instead, the dominating effect is increased carrier scattering with temperature. This results in a positive temperature coefficient of resistance: increased resistance due to a temperature increase.