Electronic Devices - Semiconductors - Discussion

It does not depend on "band gap" in diode. It depends on the "barrier". Barrier potential depends on amount of depletion region width formed. This depends upon the no. Free charges available for recombination at the junction and no immobile ions formed. So if you have more free charges during the formation of pn junction.

More recombination takes place. So we have more immobile ions at junction. Smaller gap is formed with higher density. As gap is lesser knee voltage decreases. Many have spoken about band gap of "conduction and valence bands".

Mathematically Vk = kT/e ln(NaNd/Ni^2).

With increase in temp 'T' increases but increases in Ni is high. So that Vk decreases.

According to energy band theory if temperature increases the vbi built in potential decreases. Why because due to average thermal energy kt increases more number of carriers will go into conduction band or diffusion length decreases. Or by taking potential hill negative for p side in a p-n junction it will prevent majority carriers movement from p to n side. As temp increases applied vtg increases to nullify vbi neg in p side and holes will now going to higher to lower. Diffusion process may increases due to smaller energy gap.

@ramandeep.

Barrier potential decreases with increase in temp.

From expression v. = kt/e loge NaNd/Ni^2. Itt appears barrier potential increases but due to increase in temp. There is more thermally generated charge carriers. Hence value of Ni in the expression increases. Hence net effect is that barrier potential decreases. We also have a relation change in barrier potential for silicon is -2. 5mv /c rise in temp.

In case of forward biased pn junction the energy band digram of p type move downward and n type move upward so the gap between both intrinsic fermi level decreased.ie. fi(n)+fi(p)-Vf=Vbi. Thus Vbi decreased.

Vbi = kT/e ln(NaNd/Ni^2)
since, NaNd < Ni^2
which makes ln(NaNd/Ni^2) a negetive value. When temperature increases the value of Vbi becomes more negetive or we can say its value decreases.

Vd~nVtlog(If/Is)

Is(leakage current is more sensitive to temperature than Vt(thermal voltage)...If increases, log function decreases therefore forward voltage decreases.

It decreases because as the temperature increases, electrons get excited and starts moving across the barrier. This results in decrease of barrier potential.

As the temperature increases the energy gap between valence band and conduction band decreases and hence barrier potential may also decrease.

As the temparature increases the enrgy gap between valence band and conduction band decreases and hence barrier potential may also decrease.

The built-in voltage decreases with increase in temperature due to exponential increase of intrinsic carrier concentration with temperature.