Thapar University 2006 M.E Computer Aided Design Physics of Semiconductors - Question Paper

Thapar Institute of Engineering & Technology
M.E. VLSI & CAD (1st Year)
Final Term exam
VL001 (Physics of Semiconductors)

-ijE'TwiuSX^,vⁿ

(VL-

ELECTRONICS AND COMMUNICATION ENGINEERING DEPARTMENT End Semester Examination, December 2006 M.E. (VLSI Design & CAD)- 1st Year Time Allowed : 3 Hours    Max. Marks : 45

Note : Answer any five questions.

QNo.1 a) State and explain the three important cases for movement of free electrons inside a crystal lattice. Which one is closest to electron motion inside a semiconductor and why?

b) If Pe ~ f(E) N(E) where the symbols have their usual significance. Establish the relation p = yE^,/2 for E<Ef. where y is a constant.

QNo.2 Derive an expression for the Fermi level of an extrinsic semiconductor as a function of intrinsic Fermi level E_K and material

doping levels. Under what conditions the two Fermi levels coincide.

QNO.3 Draw the energy band diagram of a Schottry Barrier diode and obtain an expression for the device capacitance. Why Vdo can not be evaluated by making measurements under forward bias?    (6+3)

QNo.4 a) Prove that for a p-n junction under thermal equilibrium the Fermi level must be a constant with respect to distance x across the device,

b) Solve the Possons equation for a p-n junction and obtain an expression for the depletion region width W". How will W be modified for an abrupt junction with No NA?

(4+5)

QNo.5 a) Draw the biasing circuit, depletion region profiles and the energy band diagram of a BJT under normal bias. Hence show how you can derive expressions for emitter current and collector current of a BJT.

b) If the transistor current gain ao = Mya_r. show when ao - *> and (ii) aofor Vcb below breakdown voltage of C-B junction.

QNo.6 a) Draw the structure of an n- channel enhancement mode MOSFET and explain its operation. What is channel length modulation and how does it affect the device characteristic and shape of the channel?

b) Show that the MOSFET drain current is linearly related to the drain voltage for Vds -> 0 and varies non-linearly for Vds Vds sat.    (6+3)

QNo.7 Write short notes on any two of the following

a)    Degenerate Semiconductors

b)    Webster effect in BJTs

c)    MOSFET capacitances and breakdown

Attachment: thapar-university-2006-m-e-computer-aided-design-26181-1.pdf

Earning:   Approval pending.