Friday, 28 June 2013

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 (300oK), 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 np doubles.

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

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