Question

For a PN junction, we have

A. Width of depletion layer

B. Junction barrier voltage

C. Reverse leakage current

Which of the above parameters will decrease when the temperature of the junction rises?

1. Only A
2. Only A and B
3. Only B and C
4. All three

Answer 1

Correct Answer - Option 2 : Only A and B

• As temperature increases, the density of carriers is increases. The applied voltage determines the amount of charge stored in the junction.
• The cross-sectional area is fixed so the depletion width is whatever value is needed so the area of the region times the number of charge carriers per cm³ equals the required charge.
• If the density of charge carriers increases, then less width is required to store the required charge. So when temperature increases, depletion width decreases.
• Barrier potential is inversely proportional to the temperature. The higher the temperature, the greater will be the mobility of charge carriers, and lower potential differences across the junction can break the potential barrier.
• But as the temperature lowers, the kinetic energy of charge carriers decreases, and higher will be the value of the potential barrier. So when temperature increases, Barrier potential decreases.

 

Under reverse bias, the T dependence of reverse leakage current is dominated by that of n_i.  Since n_i increases significantly with T, leakage current will increase significantly with T.

\(I_{RG} \propto n_i e^{qV_A / 2kT} \Rightarrow I_{RG} \propto T^{3/2} e^{(qV_A - E_G)/2kT}\)