1. Which of the following statements is correct?
a) In this figure, E1 is the
bonding orbital
b) At energy level E2 the two
atomic wave functions ψ1s
overlap in phase
EE1σ∗
E1s
E1s
EE2σ
H2
H -atom
H -atom
c) H3 molecule formation is energetically favorable
d) sp3 hybridization does not occur in case of H2
molecule formation
2. According to the FermiFermi-Dirac function, which
of the following statement is correct?
E
a) At 0K the probability of finding
an electron at an energy (EF+0.32 eV)
is less than half but not zero
T2 > T 1
T=0
EF
b) At room temperature (300K) the
probability of finding an electron
at Fermi energy is one
0
c) At high temperature (500K), where
electrons are not free, the probability
of finding an electron at Fermi energy is half
T1
1
/
2
1
f(E)
d) None of the above is correct
1
3. Consider an intrinsic semiconductor (Si) is at room
temperature, which of the following statements is correct?
a) the valance band is completely filled and the
conduction band is totally empty
b) the valance band is completely filled and the
conduction band has few electrons
c) the valance band is not completely filled and the
conduction band is not totally empty
4. Consider a pure Ge crystal is at room temperature,
which of the following statements is correct?
a) the conductivity is contributed by the free electrons in the
conduction band but not by the holes in the valance band
b) there is no hole because this is not an extrinsic
semiconductor, i.e., no doping
c) Thermal energy at room temperature (0.038 eV) is much
less than the band gap (0.66 eV) of Ge. But, hole-electron
pair generation occurs at room temperature
d) There is no charge carrier because it is a semiconductor
2
5. For a p-type semiconductor, which of the
following statement is true?
a) the Fermi energy level is always close to the
conduction band
b) the Fermi energy level moves close to the CB,
only if temperature is high enough
c) the Fermi energy is at equal distance from the
bottom of the conduction and from the top of the
valance band
d) the Fermi energy level is close the valance band
6. Write ‘T’ for true and ‘F’ for false statement
You have a small cube of n-type semiconductor. It
has plenty of free electrons in its conduction band.
But, the cube is electrically neutral
3
7. The following figure shows temperature dependency
of the carrier concentration. Which of the following
region is termed as ionization slope?
ln(n)
INTRINSIC
slope = -Eg/2k
a) region A
A
b) region B
c) region C
B
ln(Nd)
EXTRINSIC
IONIZATION
Ts
C
slope = −∆E/2k
Ti
ni(T)
1/T
8. The Si crystal shown in the figure is first doped
with 1012 As atoms. The crystal is further doped
with 1015 B atoms. Which of the following
statement is true for this Si crystal?
2 cm
a) such a doping is not possible
R
1 cm
fer
Si w a
1 mm
b) it becomes n-type
c) it becomes p-type
d) it is neither n-type nor p-type
4
9. Write “T” for true and “F” for false statement
Consider, the conduction band of an intrinsic Si
semiconductor is empty and the valance band is full.
Statement:
The valance band is actually consists of many finely
separated energy levels, which effectively becomes
continuous. Same thing (splitting) happens in the
conduction band although there is no electron in the
conduction band.
Pt (Φ=5.36 eV)
Mo (Φ=4.20 eV)
10. Two metals Pt and Mo are in contact. Which
of the following is correct?
a) electrons tunnel from Pt to Mo
b) electrons tunnel from Mo to Pt
c) electrons do not tunnel
5