C C1115 Pages 2

Reg No.:_. Name:

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION(S), MAY 2019
Course Code: EC203
Course Name: SOLID STATE DEVICES (EC,AE)
Max. Marks: 100 Duration: 3 Hours

PARTA
Answer any two full questions, each carries 15 marks. Marks
1 a) Explain Fermi Dirac distribution function. Plot the Fermi Dirac distribution (4)
function for an intrinsic semiconductor.
b) Explain diffusion. Derive an expression for diffusion current density for an n-type (7)
semiconductor.
‏و‎ A Si sample is doped with 101745 atoms/cm?. What is the equilibrium hole (4)
concentration po at 300K? Where is Er relative to 7
2 a) Draw the graph showing the distribution of excess carrierswith respect to time in (3)
an n-type semiconductor.
b) Derive the expressions for equilibrium concentration of electrons and holes using (6)
Fermi Dirac distribution function.
c) A direct bandgap semiconductor 1851 = 1010 cm? donors. Its low level carrier (6)
lifetime 715% = Tp = 1075.

i) If a sample of this material is uniformly exposed to a steady optical
generation rate of gop = 221022 EHP/cm?-s; Calculate the excess carrier
concentration An = Ap
Note : The excitation rate is not low level but assume that a, is the
same.

ii) If the carrier lifetime (t) is defined as the excess carrier concentration
divided by the recombination rate, what is t at this excitation level?

3 a) Explain High field effects. (4)

b) Derive and explain Einstein relations. (6)

c) A Ge sample is doped with 107 Boron atoms/cm*.Determine the carrier (5)
concentration & Fermi level position at room temperature.n; for Ge = 2.5 x 1013

cm? at room temperature.

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