1.
A bar of silicon with intrinsic electron density
1.4 x 1016 electronics/m3 is doped with impurity atoms
until the hole density is 8.5 x 1021 holes/m3. The motilities
of the electronics and holes are µn = 0.14 m2/V-sec and µp
= 0.05 m2/V-sec.
a.
Find the electron density of the extrinsic
material.
b.
Is the extrinsic material N-type or P-type?
c.
Find the extrinsic conductivity.
2.
How many free electrons are in one cubic inch of
N-type silicon, if the intrinsic electron density is 1.5 x 1016
electrons/m3 and the extrinsic hole density is 0.82 x 1011
holes/m3? (one inch = 2.54 cm). Assume that all donor atoms are
ionized.
3.
How many free electrons are in a bar of
extrinsic germanium measuring (4 mm) x (50 mm) x (1.5 mm) if the intrinsic hole
density is 2.4 x 1019 holes/m3 and the extrinsic hole
density is 7.85 x 1014 holes/m3? Assume that all donor
atoms are ionized.
4.
One cubic centimetre of silicon has been doped
with 1.8 x 1014 atoms of arsenic. What are the electron and hole
densities in the doped material? Assume that all impurity atoms are ionized.
5.
Find the current density in extrinsic
semiconductor at room temperature, whose hole density is 4.5 x 1018
holes/m3, when an 8 kV/m electric field intensity is established in
it?
6.
Find the total current in the extrinsic silicon
bar shown below at room temperature, if the electron density in the bar is 2.6
x 1020 electrons/m3.
7.
A bar of P-type silicon at room temperature has
a majority carrier density of 7.62 x 1022 carriers/m3. Its
cross sectional area is 2.4 x 10-6 m2. How long should
the bar be in order to have a resistance between its ends of 8.2Ω?
8.
A bar of silicon 0.1 cm long has a cross
sectional are of 8 x 10-8 m2 and is heavily doped with
phosphorous. What should be the majority carrier density if the bar is to have
a resistance of 1.5 kΩ? Assume room temperature.
9.
If donor impurity is added to the extent of 1
impurity atom in 107 germanium atoms, then find the conductivity of
doped semiconductor.
10.
Find the ratio of conductivity of N-type silicon
doped with 1 in 108 silicon atoms to that of intrinsic silicon at
room temperature.
11.
Find the conductivity of germanium, when doped
simultaneously with 1 donor in 106 Ge atoms and 1 acceptor atom in
107 Ge atoms.
12.
Calculate the electron and hole concentrations
of extrinsic silicon sample, when the conductivity is minimum. Assume µn
= 1350 cm2/V-sec and µp = 450 cm2/V-sec.
13.
If the resistivity of P-type silicon bar is 0.12
Ω-cm, then find electron and hole concentrations per cm3.
14.
A 1kΩ resistor is to be fabricated using a
P-type silicon bar with 4 mm thick, 20 µm wide and 400 µm long. Find the
required acceptor concentration per m3.
15.
Find the change in resistivity of N-type
germanium with 1 donor per 109 germanium atoms to that of intrinsic
germanium.
16.
A sample of germanium is doped to the extent of 2 x 1014 donors/cm3 and
1.5 x 1014 acceptors/cm3. At a temperature of sample, the
resistivity of pure germanium is 80 Ω-cm. Find the total current density if the
applied electric field is 5 V/cm.
17.
A block of silicon is doped with a donor atom
density of 3 x 1014 per cm3 and acceptor atom density of
0.5 x 1014 per cm3. Determine the resultant densities of
free electrons and holes per cm3.
18.
Determine the concentration of free electrons
and holes in a sample of Ge at 300oK, which has a concentration of 2
x 1014 donors/cm3 and 3 x 1014 acceptors/cm3.
19.
A sample of germanium is doped with 1014
donors/cm3 and 7 x 1013 acceptors per cm3. At
temperature of the sample, the resistivity of pure germanium is 60 Ω-cm. Assume mobility of electron is equal to
mobility of hole. Find the applied electric field if the total current density
is 52.3 mA/cm2.
20.
A cylindrically shaped section of N-type silicon
has 1 mm length and 0.1 mm2 cross sectional area. Find the ratio of
resistance of pure germanium to that of germanium doped with 8 x 1013
donors/cm3.
21.
In an N-type germanium, the resistivity is
measured to be 10-3 Ω-m, for an impurity concentration of 1022
donors/m3. Find the values of mobility and relaxation time of
electron.
22.
Calculate the position of Fermi level relative
to intrinsic Fermi level in silicon at 300oK, if the doping
concentration is 1016 donors/cm3.
23.
A silicon sample is doped with 1017
arsenic atoms/cm3.
a.
Find equilibrium hole concentration Po
at 300oK.
b.
Find the relative position of Fermi level with
respect to intrinsic Fermi level.
24.
A silicon sample is doped with 6 x 1015
donors/cm3 and 2 x 1015 acceptors/cm3. Find
the position of Fermi level with respect to intrinsic Fermi level at 300oK.
25.
In an N-type semiconductor, if the Fermi level
lies 0.6 eV below conduction band at 300oK. Find the new position of
Fermi level at 330oK.
26.
In an N-type semiconductor, Fermi level lies
0.02 eV below conduction band edge. If the donor concentration is increased by
4 times, find the new position of Fermi level.
27.
A germanium sample is doped with 1 phosphorous
atom per 108 germanium atoms. Assume effective mass of electron is
half of its true mass. At what doping level (ND), Fermi level
coincides with conduction band edge.
28.
A silicon sample is doped with 1 donor atom per
2 x 108 silicon atoms. Assume effective mass of electron is same as
its true mass. Find the temperature, at which Fermi level coincides with
conduction band edge.
29.
How much donor impurity should be added to pure
germanium, so that its resistivity drops to 10% of its original value?
30.
Find the concentration of holes and electrons in
P-type germanium at room temperature, if the resistivity is 0.02 Ω-cm.
31.
Find the resistivity if a donor type impurity is
added to the extent of 1 atom per 108 germanium atoms.
32.
A donor type impurity is added and the resistivity
decreases to 9.6 Ω-cm. Compute the ratio
of donor atoms to silicon atoms per unit volume.
33.
Determine the concentration of free electrons
and holes in a sample of silicon at 500oK, which has a concentration
of donors equal to ND = 1.874 x 1013 atoms/cm3
and of acceptor atoms equal to NA = 3.748 x 1013 atoms/cm3.
Show that the sample is essentially intrinsic. Explain why.
Where can I find the solution to these practice questions?
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