Video Solutions for GATE 1990 ECE : Five Mark Questions ( Electron Devices )

1.       (a) Two ideal and identical (ideality factor ƞ = 1)  

                junction diodes are connected in series as  

            shown in figure.

      Show that

 exp (eV₁/KT)  +  exp (-eV₂/KT) = 2

                                where V₁ and V₂ are the voltage drops across  

                                the diodes D1 and D2.

                   (b) Assuming that the current through the reverse 

                         biased diode is saturated at Io.

                         Calculate the voltage drop across the forward 

                          biased diode. 

                         Assume KT = 26meV. 

2.       In a semiconductor at room temperature (300^oK), the intrinsic carrier concentration and resistivity are 1.5 X 10¹⁶ m³ and 2 X 10 Ω-m respectively. It is converted into an extrinsic semiconductor with a doping concentration of 10²⁰/m³. For the extrinsic semiconductor, calculate the

a.       Minority carrier concentration

b.      Resistivity

c.       Shift in Fermi level due to doping

d.      Minority carrier concentration when its temperature is increased to a value at which the intrinsic carrier concentration n_p doubles.

        Assume the mobility of minority and majority carriers to be the same and KT = 26 meV at room temperature.