I was working on the temperature dependence of the Mosfet and I obtained the following characteristics shown below. Interestingly the drain current decreases with increasing temperature. But thought that temperature increases the energy of the electrons thereby it should cause a higher current is it not ? Why would it be otherwise ? In the graph shown below Vgs was constant and the Vds was varied for different temperature values and you can see that the current decreases for higher temperatures.
those look like you have saturation and a high gate voltage above Vt, so VDSat approx is sqrt(Is *Isat)/Ut (that's the behavior, not the complete equation), where Ut is the thermal voltage. The drain current would decrease as the temperature goes up.
As the temperature increases, the meantime of collisions goes up, which causes those "higher order effects" that slows down mobility.
If we had a benefit from higher temperatures, we wouldn't need heatsinks.
The drain current depends on carrier mobility (which decreases with increasing temperature by about -0.3 %/deg C); carrier concentration (which increases negligible with temperature), and threshold voltage (which decrease with temperature by about -2 mV/deg. C).
At gate voltages just above the threshold voltage (say < 500 mV above), the threshold variation dominates, and drain current increases with temperature. Conversely, at significantly higher gate voltages (say more than 1 V above threshold), the mobility term dominates, and drain current decreases with temperature.
IN MOSFETs, generally it works in inversion mode in which (for n channel mosfet) electrons make a channel due to high electric field between gate terminal to substrate . when temperature increases, electrons will gain kinetic energy and this will be a barrier for electrons moving towards channel in the influence of electric field to create channel which means now either we need to increase gate voltage to get the same amount of current (current at previous temperature). or if we make gate voltage constant then current will decrease due to extra gained kinetic energy which decreases the influence of electric field .