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b) A silicon sample doped with 2x10'°cm® of Boron atoms. ( ಗಿ 1.5210 ‏تو"‎

for Silicon at 300 K) Determine,
i. The equilibrium electron and hole concentrations
ii. Position of fermi energy level in the band gap
111. Plot the energy band diagram

a) Plot and explain the temperature dependence of intrinsic carrier concentration
in semiconductors

b) With suitable sketches explain the indirect recombination mechanism via
traps.

९) An n-type Si sample with Nd = 107 cm” is steadily illuminated such that gop
=107! EHP/cm’s, If ಸಾರ Tp = | us for this excitation, calculate the separation in
the quasi-Fermi levels, (F, - F,). (nj= 1.5% 10'°cm® for Silicon at 300 K)

Module 2

a) Explain the term mobility with respect to semiconductors. What are the
factors on which the mobility depends on? Explain the variation of mobility
with temperature and doping.

b) A potential of 100 mV is applied across a semiconductor bar, and the
resulting current is 1 mA. A magnetic field of 10* Wb/cm” is applied
perpendicular to this semiconductor bar. The hall voltage measured is -2
mV. The dimensions of the bar are width = 0.1 mm, length = 5 mm and
thickness = 10 um. Find

i. the type of the semiconductor bar
ii. 0൦ concentration and the mobility of majority carriers

a) Derive continuity equation for holes.

b) Solve the continuity equation, under steady state conditions assuming the
semiconductor is long and no drift current is present. Plot the solution.

c) A p type semiconductor injected at one end with minority carrier electrons,
under steady state conditions. Na = 1015 ला > , ‏مہ‎ = 0.1 us, [0 = 700 cm7/V
Sec. Calculate the electron diffusion length.

Module 3

a) With the help of energy band diagrams, explain the behaviour of the contact

between a metal and an n -type semiconductor. Clearly distinguish between

Schottky and ohmic contacts.

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