In a semiconductor, the forbidden energy gap between the valence band and the conduction band is of the order is
1.1 MeV
2.0.1 Mev
3.1 eV
4. 5 eV
Let nh and ne be the number of holes and conduction electrons in an extrinsic semiconductor. Then
1. nh > ne
2.nh = ne
3.nh < ne
4.nh ≠ne
The electrical conductivity of pure germanium can be increased by
1.increasing the temperature
2.doping acceptor impurities
3.doping donor impurities
4.All of the above
What happens to the resistance of a pure semiconductor when heated?
1.The resistance increases
2.The resistance decreases
3.The temperature remains the same
4.Can’t say
A forward biased pn junction has a resistance of the ……..
1.order of Ω
2.order of kΩ
3.order of MΩ
4.none of the above
A hole and electron in close proximity would tend to ……..
1.repel each other
2.attract each other
3.have no effect on each other
4.none of the above
A pn junction acts as a ……..
1.controlled switch
2.bidirectional switch
3.unidirectional switch
4.none of the above
A reverse biased pn junction has ……..
1.very narrow depletion layer
2.almost no current
3.very low resistance
4.large current flow
A reverse biased pn junction has resistance of the……..
1.order of Ω
2.order of kΩ
3.order of MΩ
4.none of the above
An electron and a hole in close proximity would tend to _____.
1.attract each other
2.repel each other
3.have no effect on each other
4.destroy each other
An electron and a hole in close proximity would tend to _____.
1.attract each other
2.repel each other
3.have no effect on each other
4.destroy each other
As the doping to a pure semiconductor increases, the bulk resistance of the semiconductor ……..
1.remains the same
2.increases
3.decreases
4.none of the above
At absolute temperature, an intrinsic semiconductor has …….
1.a few free electrons
2.many holes
3.many free electrons
4.No holes or free electrons
At absolute zero, Si acts as
1.non-metal
2.metal
3.insulator
4.None of these
At room temperature, an intrinsic semiconductor has ……..
1.many holes only
2.a few free electrons and holes
3.many free electrons only
4.No holes or free electrons
At room temperature, an intrinsic silicon crystal acts approximately as ……..
1.a battery
2.a conductor
3.an insulator
4.A piece of copper wire
Electric conduction in a semiconductor takes place due to
1. electrons only
2.holes only
3. both electrons and holes
4.neither electrons nor holes
How many valence electrons do trivalent impurities have?
1.2
2.3
3.4
4.5
How many valence electrons does a pentavalent impurity have?
1.3
2.4
3.5
4.6
In a p-type semiconductor, the acceptor valence band is
1.close to the valence band of the host crystal
2. close to conduction band of the host crystal
3.below the conduction band of the host crystal
4.above the conduction band of the host crystal
In a semiconductor
1.there are no free electrons at 0 K
2. there are no free electrons at any temperature
3. the number of free electrons increases with pressure
4.the number of free electrons is more than that in a conductor
In a semiconductor, current conduction is due ……..
1.only to holes
2.only to free electrons
3.to holes and free electrons
4.none of the above Answer: to holes and free electrons
In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of
1.1 MeV
2.0.1 MeV
3.1 eV
4.5 eV
In an intrinsic semiconductor, the number of free electrons ……..
1.equals the number of holes
2.is greater than the number of holes
3.is less than the number of holes
4.none of the above
In an n-type semiconductor, donor valence band is
1.above the conduction band of the host crystal
2. close to the valence band of the host crystal
3.close to the conduction band of the host crystal
4. below the valence band of the host crystal
In semiconductors, at room temperature
1.the conduction band is completely empty
2.the valence band is partially empty and the conduction band is partially filled
3. the valence band is completely filled and the conduction band is partially filled
4.the valence band is completely filled
In the depletion region of a pn junction, there is a shortage of ……….
1.acceptor ions
2.holes and electrons
3.donor ions
4.none of the above
One serious drawback of semi-conductor devices is
1. they do not last for long time.
2.they are costly
3.they cannot be used with high voltage.
4. they pollute the environment.
Temperature coefficient of resistance of semiconductor is
1. zero
2.constant
3.positive
4. Negative
The barrier voltage at a pn junction for germanium is about ……..
1.3.5 V
2.3V
3.zero
4.0.3 V
The battery connections required to forward bias a pn junction are ……..
1.+ve terminal to p and −ve terminal to n
2.−ve terminal to p and +ve terminal to n
3.−ve terminal to p and −ve terminal to n
4.none of the above
The forbidden energy gap for germanium crystal at 0 K is
1.0.071 eV
2.0.71 eV
3.2.57 eV
4.6.57 eV
The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of
1.phosphorus
2. boron
3.antimony
4.nitrogen
The impurity level in an extrinsic semiconductor is about …….. of pure semiconductor.
1.10 atoms for 108 atoms
2.1 atom for 108 atoms
3.1 atom for 104 atoms
4.1 atom for 100 atoms
The leakage current across a pn junction is due to ……..
1.minority carriers
2.majority carriers
3.junction capacitance
4.none of the above
The leakage current in a pn junction is of the order of ……..
1.A
2.mA
3.kA
4.μA
The mobility of free electrons is greater than that of free holes because
1. they are light
2.they carry negative charge
3.they mutually collide less
4.they require low energy to continue their motion
The random motion of holes and free electrons due to thermal agitation is called ……..
1.diffusion
2.pressure
3.ionisation
4.none of the above
The relation between number of free electrons (n) in a semiconductor and temperature (T) is given by
1. n α T
2.n α T2
3.n α √T
4.n α T3/2
The resistivity of a semiconductor at room temperature is in between
1.10–2 to 10–5 Ω cm
2.10–3 to 106 Ω cm
3.106 to 108 Ω cm
4.1010 to 1012 Ω cm
What is the random motion of free electrons and holes due to thermal agitation called?
1.Pressure
2.Diffusion
3.Ionisation
4.none of the above
What is the resistivity of a pure semiconductor at absolute zero ?
1.Zero
2.Infinity
3. Same as that of conductors at room temperature
4.Same as that of insulators at room temperature
When the temperature of an extrinsic semiconductor is increased, the pronounced effect is on ……..
1.junction capacitance
2.minority carriers
3.majority carriers
4.none of the above
Which among the following is the most commonly used semiconductor?
1.Silicon
2.Carbon
3.Germanium
4.Sulphur
Which of the following does a hole in the semiconductor define?
1.A free proton
2.A free neutron
3.A free-electron
4.An incomplete part of an electron pair bond
Which of the following does the resistivity of a semiconductor depend upon?
1.Length of the semiconductor
2.Atomic nature of the semiconductor
3.Shape and atomic nature of the semiconductor
4.Shape of semiconductor
Which of the following is created when trivalent impurities are added to a semiconductor?
1.Free electrons
2.Holes
3.Bound electrons
4.Valence electrons
Which of the following statements is true about extrinsic semiconductors?
1.The gap between the conduction band and the valence bond is more than 16 eV
2.The gap between the conduction band and the valence bond is about 1 eV
3.The gap between the conduction band and valence band is 100 eV and more
4.The conduction band and the valence band overlap.
Why is the mobility of free electrons greater than that of holes?
1.They are light
2.They mutually collide less
3.They require low energy to continue the motion
4.They carry negative energy
With forward bias to a pn junction, the width of depletion layer ……..
1.decreases
2.increases
3.remains the same
4.none of the above