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

junction diodes are connected in series as

shown in figure.

Show that

exp (eV

_{1}/KT) + exp (-eV_{2}/KT) = 2
where V

_{1}and V_{2}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

^{o}K), the intrinsic carrier concentration and resistivity are 1.5 X 10^{16}m^{3}and 2 X 10 Ω-m respectively. It is converted into an extrinsic semiconductor with a doping concentration of 10^{20}/m^{3}. 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.

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