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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