8/9/2019 Semicond Specimen

1/7

Index Number: ___________________

Specimen Paper

TEL204/05 Semiconductor Device P!"ic"

Time: # $our"

In"truction" to candidate":

1. Please check that this question paper consists of six (6) printed pages beforeyou begin the examination.

2. Anser any ! questions in the anser booklet pro"ided.

#. $on%programmable electronic calculator may be used.

&. 'ou may refer to the Appendix for formulas and physical constants.

!. 'ou are not alloed to remo"e this question paper from the examination "enue.

opyright 2*1# +,-

2%

8/9/2019 Semicond Specimen

2/7

TEL204/05

%ue"tion & '20 mar(")

(a) /ketch the crystal structure for simple cubic structure and body%centeredcubic structure. 0! marks

(b) he diamond lattice structure is the basic building block in silicon.(i) alculate the number of atoms in one cell of a diamond structure.0! marks

(ii) alculate the density of atoms in silicon in terms of atomsm#.0! marks

(c) he energy le"els in the hydrogen atom as proposed by 3ohr ha"ediscrete energy le"els ith principal quantum number n as shon in thefigure belo.

4igure 1

5i"en that the electron energy in the hydrogen atom 26.13n

En

= e7

8etermine the energy released hen an electron mo"es from energyle"els 9#to 91. 0! marks

%ue"tion 2 '20 mar(")

(a) 5i"en to doped silicon samples : and '. /ample : doped ith 1610

nitrogen atomscm 3 ; /ample ' doped ith 5 1013 aluminum atomscm3 .

(i) /tate the type of semiconductor for sample : and sample '.0& marks(ii) 4ind the ma

8/9/2019 Semicond Specimen

3/7

TEL204/05

%ue"tion # '20 mar(")

(a) A rectangular germanium block ith the dimensions as shon in the figure belohas a resisti"ity of 1*#m at 2*B.

4igure 1(i) 4ind the resistance beteen the square ends.

0& marks

(ii) 4ind the resistance beteen the rectangular ends.0& marks

(iii) A 1*mA current flos beteen the rectangular ends. 4ind the number ofelectrons passing the silicon block per second.

0& marks

(b) 3riefly explain the reason direct band gap semiconductor is more suitable to beused in optoelectronics applications. /ketch and label the energy band diagramof a direct band gap semiconductor and an indirect band gap

semiconductor.0> marks

%ue"tion 4 '20 mar(")(a) (i) +hat are the important points of CeisenbergDs uncertainty principleE

06 marks (ii) he uncertainty in the position of a particle ha"ing mass ?.11x1*%#1=g is >F

4ind the uncertainty in the momentum 02

hxp = of the particle.

0& marks (iii) An electron is mo"ing ith a "elocity of 1x1*Gcms. 8etermine its associated

de 3roglie a"elength 0Hhp here h is PlanckDs constant and p is

momentum. 0! marks

(b) 5i"en a sample of intrinsic silicon and a sample of intrinsic germanium ithsame dimensions for both samples. At room temperature hich sample hashigher resisti"ityE Iustify your anser.

0! marks

#

8/9/2019 Semicond Specimen

4/7

TEL204/05

&

&%

8/9/2019 Semicond Specimen

5/7

TEL204/05

%ue"tion 5 '20 mar(")

(a) 3riefly describe the particle in a box model in quantum mechanics. 02 marks

(b) Sketch the initial a"e functions for the first four energy states in a one%

dimensional particle in a box gi"en that 9*is the energy at ground state (nH1).

Label your diagram clearly. [8 marks]

(c) esium chloride (sl) is a typical body%centred cubic ionic structure ith the@adelung constant J H 1.G62G. Kt is gi"en that its aoH *.#!6 nm and n H 1*.!.4ind theL

(i) 3inding energy energy of sl in terms of e7. 0# marks(ii) @olar ohesi"e energy of sl in terms of kJ/mol. 0# marks

(d) he energy difference beteen the !d and 6s suble"els in gold accounts for its

color. Assuming this energy difference is about 2.G e7 explain hy gold has a

arm yello color.. [4 marks]

%ue"tion * '20 mar(")

(a) 4or an Al%/i,2%/i capacitor the doping of the substrate is $aH1*1&cm%# and the

oxide thickness is >2F. 5i"en that the flat band "oltage 743is M *.& 7 calculate

at strong in"ersion

(i) the surface potential

0& marks

(ii) the maximum depletion layer idth

02 marks

(iii) the gate "oltage

0& marks

(b) Nualitati"ely explain ho the oxide charges affect the threshold "oltage.

0& marks

(c)Oist to differences beteen ionic, covalent and metallic bonds. 06

marks

!

8/9/2019 Semicond Specimen

6/7

TEL204/05

+ppendix I

P!"ica, con"tant"

3oltmann constant k = 1 38 10 23. I=

Planck constant 341063.6

=h Is9lementary charge C1060.1 19=q

Permitti"ity in "acuum o =

8 85 10 12

. F / m

Permeability in "acuum o =

4 10 7

H / m

9lectron rest mass mo =

9 11 10 31

. kg

hermal "oltagekT

q = 0 0259. V (at T H #**=)

able 1L Properties of semiconductors and insulator (at #**= unless otherise noted)

Propert! -nit" Si .e .a+" Si2Lattice constant nm *.!*G *.!6!G! *.!6!#2 %

Density gcm# !.** Q 1*22 &.&2 Q 1*22 2.21 Q 1*222.2* Q1*22

Energy gap at300 K

e7 1.12& *.6G 1.&2 > M ?

Energy gap at 0K

e7 1.1G* *.G&& 1.!2 %

Relativepermittivity

% 11.G 16.* 1#.1 #.?

Intrinsic carrierconcentration cm# 1.&! Q 1*1* 2.& Q 1*1# ?.* Q 1*6 %Electron lattice

mobilitycm27s 1&1G #?** >>** 2*

Hole latticemobility

cm27s &G1 1?** &** 1*>

Effective densityof states in

conduction bandcm# 2.> Q 1*1? 1.*& Q 1*1? &.G Q 1*1G %

Effective densityof states in

valence bandcm# 1.*& Q 1*1? 6.* Q 1*1> G.* Q 1*1> %

Electroneffective mass

mn*mo 1.*> *.!! *.*6> %

Hole effectivemass

mp*mo *.>1 *.# *.! %

Electron affinity e7 &.*! &.** &.*G 1.*

6

G%

8/9/2019 Semicond Specimen

7/7

TEL204/05

+ppendix II

ormu,a" Seet

Binding energy )1

1)(4

(00

2

na

eB =

Molar cohesive energy C = B

(2NA

Kn the photoelectric effect the cutoff

a"elength

hc

c =

he maximum kinetic energy

K hhc

max = =

he stopping potentiale

KV

s

max=

he minimum frequency of photon

h

Ef

g=

he energy bandgap of /i

T

TEE gg

+

=

2)0(

Kntrinsic carrier concentration of

silicon ]exp[2kT

ENNn

g

vci

=

oncentration of ma