Solved Example: Semiconductor Electronics Material Devices and Circuits | Physics for JEE Main & Advanced PDF Download

 Page 1


JEE Solved Examples on Semiconductor Electronics: 
Material Devices and Circuits 
JEE Mains 
Q1:  The forbidden energy gap of a germanium semiconductor is ?? . ???????? . The minimum thermal 
energy of electrons reaching the conduction band from the valence band should be 
(A) ?? . ?????? 
(B) ?? . ???????? 
(C) ?? . ???????? 
(D) ?? . ?????? 
Ans: (B) ?? 9
= 0.75eV 
 
Q2:  The energy of a photon of sodium light (?? = ???????? ?? ) equal the band gap of a semiconductor. 
The minimum energy required to create an electron-hole pair is 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ?????? 
(D) ?? . ?????? 
Ans: (C) Minimum energy required to create e - h pair =
12400
5890
= 2.1eV 
 
Q3:  On increasing temperature the specific resistance of a semiconductor 
(A) Decreases 
(B) Increases 
(C) Remains constant 
(D) Become zero 
Ans: (B) On increasing temperature, energy of electron increases so they can easily jump in 
conductor band so resistance increase. 
 
Q4:  In a good conductor the energy gap between the conduction band and the valence band is - 
(A) Infinite 
(B) Wide 
(C) Narrow 
(D) Zero 
Ans:  (D) In a good conductor, energy band gap is zero as conduction and valence band overlap. 
 
 
Page 2


JEE Solved Examples on Semiconductor Electronics: 
Material Devices and Circuits 
JEE Mains 
Q1:  The forbidden energy gap of a germanium semiconductor is ?? . ???????? . The minimum thermal 
energy of electrons reaching the conduction band from the valence band should be 
(A) ?? . ?????? 
(B) ?? . ???????? 
(C) ?? . ???????? 
(D) ?? . ?????? 
Ans: (B) ?? 9
= 0.75eV 
 
Q2:  The energy of a photon of sodium light (?? = ???????? ?? ) equal the band gap of a semiconductor. 
The minimum energy required to create an electron-hole pair is 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ?????? 
(D) ?? . ?????? 
Ans: (C) Minimum energy required to create e - h pair =
12400
5890
= 2.1eV 
 
Q3:  On increasing temperature the specific resistance of a semiconductor 
(A) Decreases 
(B) Increases 
(C) Remains constant 
(D) Become zero 
Ans: (B) On increasing temperature, energy of electron increases so they can easily jump in 
conductor band so resistance increase. 
 
Q4:  In a good conductor the energy gap between the conduction band and the valence band is - 
(A) Infinite 
(B) Wide 
(C) Narrow 
(D) Zero 
Ans:  (D) In a good conductor, energy band gap is zero as conduction and valence band overlap. 
 
 
Q5:  In a semiconducting material the mobilities of electrons and holes are ?? ?? and ?? ?? respectively. 
Which of the following is true 
(A) ?? ?? > ?? ?? 
(B) ?? ?? < ?? ?? 
(C) ?? ?? = ?? ?? 
(D) ?? ?? < ?? ; ?? ?? > ?? 
Ans: (A) Movement of holes involve breaking and joining of bonds so mobility of holes is less than 
that of electrons. 
 
Q6:  Those materials in which number of holes in valence band is equal to number of electrons in 
conduction band are called 
(A) Conductors 
(B) Intrinsic semiconductors 
(C) p-type semiconductors 
(D) n-type semiconductors 
Ans: (B) No of electron and hole pairs are equal in intrinsic semiconductors. 
 
Q7:  In p-type semiconductor holes move in 
(A) Forbidden region 
(B) Conduction band 
(C) Valence band 
(D) all the above regions 
Ans: (C) 
 
Holes move in valence band in p-type semiconductors 
 
Q8:  Fermi level of energy of intrinsic semiconductor lies- 
(A) In the middle of forbidden gap 
(B) Below the middle of forbidden gap 
(C) Above the middle of forbidden gap 
(D) Outside the forbidden gap 
Ans: (A) For intrinsic semiconductors fermi level of energy lies in the middle of forbidden gap. 
Page 3


JEE Solved Examples on Semiconductor Electronics: 
Material Devices and Circuits 
JEE Mains 
Q1:  The forbidden energy gap of a germanium semiconductor is ?? . ???????? . The minimum thermal 
energy of electrons reaching the conduction band from the valence band should be 
(A) ?? . ?????? 
(B) ?? . ???????? 
(C) ?? . ???????? 
(D) ?? . ?????? 
Ans: (B) ?? 9
= 0.75eV 
 
Q2:  The energy of a photon of sodium light (?? = ???????? ?? ) equal the band gap of a semiconductor. 
The minimum energy required to create an electron-hole pair is 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ?????? 
(D) ?? . ?????? 
Ans: (C) Minimum energy required to create e - h pair =
12400
5890
= 2.1eV 
 
Q3:  On increasing temperature the specific resistance of a semiconductor 
(A) Decreases 
(B) Increases 
(C) Remains constant 
(D) Become zero 
Ans: (B) On increasing temperature, energy of electron increases so they can easily jump in 
conductor band so resistance increase. 
 
Q4:  In a good conductor the energy gap between the conduction band and the valence band is - 
(A) Infinite 
(B) Wide 
(C) Narrow 
(D) Zero 
Ans:  (D) In a good conductor, energy band gap is zero as conduction and valence band overlap. 
 
 
Q5:  In a semiconducting material the mobilities of electrons and holes are ?? ?? and ?? ?? respectively. 
Which of the following is true 
(A) ?? ?? > ?? ?? 
(B) ?? ?? < ?? ?? 
(C) ?? ?? = ?? ?? 
(D) ?? ?? < ?? ; ?? ?? > ?? 
Ans: (A) Movement of holes involve breaking and joining of bonds so mobility of holes is less than 
that of electrons. 
 
Q6:  Those materials in which number of holes in valence band is equal to number of electrons in 
conduction band are called 
(A) Conductors 
(B) Intrinsic semiconductors 
(C) p-type semiconductors 
(D) n-type semiconductors 
Ans: (B) No of electron and hole pairs are equal in intrinsic semiconductors. 
 
Q7:  In p-type semiconductor holes move in 
(A) Forbidden region 
(B) Conduction band 
(C) Valence band 
(D) all the above regions 
Ans: (C) 
 
Holes move in valence band in p-type semiconductors 
 
Q8:  Fermi level of energy of intrinsic semiconductor lies- 
(A) In the middle of forbidden gap 
(B) Below the middle of forbidden gap 
(C) Above the middle of forbidden gap 
(D) Outside the forbidden gap 
Ans: (A) For intrinsic semiconductors fermi level of energy lies in the middle of forbidden gap. 
. 
 
Q9:  The electron mobility in ?? -type germanium is 3900 ????
?? / V.s and its conductivity is 
?? . ?????????? /???? , then impurity concentration will be if the effect of cotters is negligible - 
(A) ????
????
 ????
?? 
(B) ????
????
/????
?? 
(C) ????
????
/????
?? 
(D) ????
????
/????
?? 
Ans: (D) ?? = ?? (?? ?? ?? ?? + ?? ?? ?? ?? ) 
?? ?? >> ?? h
 
So, ?? = ?? ?? ?? ?? ?? ? ?? ?? =
?? ?? ?? ?? =
6.24
3900×1.6×10
-19
 
= 10
16
/cm
3
 
Hence the answer is B 
Q10:  The approximate radio of resistances in the forward and reverse bias of the ???? -junction 
diode is- 
(A) ????
?? : ?? 
(B) ????
-?? : ?? 
(C) ?? : ????
-?? 
(D) ?? : ????
?? 
Ans: (D) Resistance in forward bias is much less than resistance in the reverse bias and the ratio of 
resistances is approximately 1: 10
4
 (Theoretical fact) 
Q11:  The diode used in the circuit shown in the figure has a constant voltage drop of ?? . ?? ?? at all 
current and a maximum power rating of 100 milliwatts. What should be the value of the resistor ?? , 
connected in series with the diode for obtaining maximum current-? 
 
(A) ?? . ???? 
(B) ???? 
(C) ?? . ?????? 
(D) ???????? 
Ans: (B) Given: 
• Diode's Voltage Drop, V
d
= 0.5 V 
• Maximum Power Rating, P = 100 mW = 0.1 Watts 
• Battery EMF, E = 1.5 V 
• Resistance = ?? 
Page 4


JEE Solved Examples on Semiconductor Electronics: 
Material Devices and Circuits 
JEE Mains 
Q1:  The forbidden energy gap of a germanium semiconductor is ?? . ???????? . The minimum thermal 
energy of electrons reaching the conduction band from the valence band should be 
(A) ?? . ?????? 
(B) ?? . ???????? 
(C) ?? . ???????? 
(D) ?? . ?????? 
Ans: (B) ?? 9
= 0.75eV 
 
Q2:  The energy of a photon of sodium light (?? = ???????? ?? ) equal the band gap of a semiconductor. 
The minimum energy required to create an electron-hole pair is 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ?????? 
(D) ?? . ?????? 
Ans: (C) Minimum energy required to create e - h pair =
12400
5890
= 2.1eV 
 
Q3:  On increasing temperature the specific resistance of a semiconductor 
(A) Decreases 
(B) Increases 
(C) Remains constant 
(D) Become zero 
Ans: (B) On increasing temperature, energy of electron increases so they can easily jump in 
conductor band so resistance increase. 
 
Q4:  In a good conductor the energy gap between the conduction band and the valence band is - 
(A) Infinite 
(B) Wide 
(C) Narrow 
(D) Zero 
Ans:  (D) In a good conductor, energy band gap is zero as conduction and valence band overlap. 
 
 
Q5:  In a semiconducting material the mobilities of electrons and holes are ?? ?? and ?? ?? respectively. 
Which of the following is true 
(A) ?? ?? > ?? ?? 
(B) ?? ?? < ?? ?? 
(C) ?? ?? = ?? ?? 
(D) ?? ?? < ?? ; ?? ?? > ?? 
Ans: (A) Movement of holes involve breaking and joining of bonds so mobility of holes is less than 
that of electrons. 
 
Q6:  Those materials in which number of holes in valence band is equal to number of electrons in 
conduction band are called 
(A) Conductors 
(B) Intrinsic semiconductors 
(C) p-type semiconductors 
(D) n-type semiconductors 
Ans: (B) No of electron and hole pairs are equal in intrinsic semiconductors. 
 
Q7:  In p-type semiconductor holes move in 
(A) Forbidden region 
(B) Conduction band 
(C) Valence band 
(D) all the above regions 
Ans: (C) 
 
Holes move in valence band in p-type semiconductors 
 
Q8:  Fermi level of energy of intrinsic semiconductor lies- 
(A) In the middle of forbidden gap 
(B) Below the middle of forbidden gap 
(C) Above the middle of forbidden gap 
(D) Outside the forbidden gap 
Ans: (A) For intrinsic semiconductors fermi level of energy lies in the middle of forbidden gap. 
. 
 
Q9:  The electron mobility in ?? -type germanium is 3900 ????
?? / V.s and its conductivity is 
?? . ?????????? /???? , then impurity concentration will be if the effect of cotters is negligible - 
(A) ????
????
 ????
?? 
(B) ????
????
/????
?? 
(C) ????
????
/????
?? 
(D) ????
????
/????
?? 
Ans: (D) ?? = ?? (?? ?? ?? ?? + ?? ?? ?? ?? ) 
?? ?? >> ?? h
 
So, ?? = ?? ?? ?? ?? ?? ? ?? ?? =
?? ?? ?? ?? =
6.24
3900×1.6×10
-19
 
= 10
16
/cm
3
 
Hence the answer is B 
Q10:  The approximate radio of resistances in the forward and reverse bias of the ???? -junction 
diode is- 
(A) ????
?? : ?? 
(B) ????
-?? : ?? 
(C) ?? : ????
-?? 
(D) ?? : ????
?? 
Ans: (D) Resistance in forward bias is much less than resistance in the reverse bias and the ratio of 
resistances is approximately 1: 10
4
 (Theoretical fact) 
Q11:  The diode used in the circuit shown in the figure has a constant voltage drop of ?? . ?? ?? at all 
current and a maximum power rating of 100 milliwatts. What should be the value of the resistor ?? , 
connected in series with the diode for obtaining maximum current-? 
 
(A) ?? . ???? 
(B) ???? 
(C) ?? . ?????? 
(D) ???????? 
Ans: (B) Given: 
• Diode's Voltage Drop, V
d
= 0.5 V 
• Maximum Power Rating, P = 100 mW = 0.1 Watts 
• Battery EMF, E = 1.5 V 
• Resistance = ?? 
1 Finding Current in the Circuit: 
So it's given E = 1.5 V and Vd = 0.5 V 
Formula: P = I
*
???? ? I = (P/Vd) 
I = (0.1/0.5) = 0.2 A 
2 Finding Potential Drop Across ?? 
V = E - Vd = 1.5 - 0.5 = 1 V 
3 Finding Value of ?? 
From above, 
?? = 1?? and ?? = 0.2 A
?? = ?????? = ?? /?? = 1/0.2 = 5 ohms 
 
 
 
Q12: In the following circuits ???? -junction diodes ?? ?? ' ?? ?? and ?? ?? are ideal for the following 
potential of ?? and ?? , the correct increasing order of resistance between ?? and ?? will be 
 
(i) -???? ?? , -?? ?? 
(ii) -?? ?? , -???? ?? 
(iii) -?? ?? , -???? ?? 
(A) (i) < (ii) < (iii) 
(B) (iii) < (ii) < (i) 
(C) (ii) = (iii) < (i) 
(D) (i) = (iii) < (i) 
Ans: (C) (i) 
 
Page 5


JEE Solved Examples on Semiconductor Electronics: 
Material Devices and Circuits 
JEE Mains 
Q1:  The forbidden energy gap of a germanium semiconductor is ?? . ???????? . The minimum thermal 
energy of electrons reaching the conduction band from the valence band should be 
(A) ?? . ?????? 
(B) ?? . ???????? 
(C) ?? . ???????? 
(D) ?? . ?????? 
Ans: (B) ?? 9
= 0.75eV 
 
Q2:  The energy of a photon of sodium light (?? = ???????? ?? ) equal the band gap of a semiconductor. 
The minimum energy required to create an electron-hole pair is 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ?????? 
(D) ?? . ?????? 
Ans: (C) Minimum energy required to create e - h pair =
12400
5890
= 2.1eV 
 
Q3:  On increasing temperature the specific resistance of a semiconductor 
(A) Decreases 
(B) Increases 
(C) Remains constant 
(D) Become zero 
Ans: (B) On increasing temperature, energy of electron increases so they can easily jump in 
conductor band so resistance increase. 
 
Q4:  In a good conductor the energy gap between the conduction band and the valence band is - 
(A) Infinite 
(B) Wide 
(C) Narrow 
(D) Zero 
Ans:  (D) In a good conductor, energy band gap is zero as conduction and valence band overlap. 
 
 
Q5:  In a semiconducting material the mobilities of electrons and holes are ?? ?? and ?? ?? respectively. 
Which of the following is true 
(A) ?? ?? > ?? ?? 
(B) ?? ?? < ?? ?? 
(C) ?? ?? = ?? ?? 
(D) ?? ?? < ?? ; ?? ?? > ?? 
Ans: (A) Movement of holes involve breaking and joining of bonds so mobility of holes is less than 
that of electrons. 
 
Q6:  Those materials in which number of holes in valence band is equal to number of electrons in 
conduction band are called 
(A) Conductors 
(B) Intrinsic semiconductors 
(C) p-type semiconductors 
(D) n-type semiconductors 
Ans: (B) No of electron and hole pairs are equal in intrinsic semiconductors. 
 
Q7:  In p-type semiconductor holes move in 
(A) Forbidden region 
(B) Conduction band 
(C) Valence band 
(D) all the above regions 
Ans: (C) 
 
Holes move in valence band in p-type semiconductors 
 
Q8:  Fermi level of energy of intrinsic semiconductor lies- 
(A) In the middle of forbidden gap 
(B) Below the middle of forbidden gap 
(C) Above the middle of forbidden gap 
(D) Outside the forbidden gap 
Ans: (A) For intrinsic semiconductors fermi level of energy lies in the middle of forbidden gap. 
. 
 
Q9:  The electron mobility in ?? -type germanium is 3900 ????
?? / V.s and its conductivity is 
?? . ?????????? /???? , then impurity concentration will be if the effect of cotters is negligible - 
(A) ????
????
 ????
?? 
(B) ????
????
/????
?? 
(C) ????
????
/????
?? 
(D) ????
????
/????
?? 
Ans: (D) ?? = ?? (?? ?? ?? ?? + ?? ?? ?? ?? ) 
?? ?? >> ?? h
 
So, ?? = ?? ?? ?? ?? ?? ? ?? ?? =
?? ?? ?? ?? =
6.24
3900×1.6×10
-19
 
= 10
16
/cm
3
 
Hence the answer is B 
Q10:  The approximate radio of resistances in the forward and reverse bias of the ???? -junction 
diode is- 
(A) ????
?? : ?? 
(B) ????
-?? : ?? 
(C) ?? : ????
-?? 
(D) ?? : ????
?? 
Ans: (D) Resistance in forward bias is much less than resistance in the reverse bias and the ratio of 
resistances is approximately 1: 10
4
 (Theoretical fact) 
Q11:  The diode used in the circuit shown in the figure has a constant voltage drop of ?? . ?? ?? at all 
current and a maximum power rating of 100 milliwatts. What should be the value of the resistor ?? , 
connected in series with the diode for obtaining maximum current-? 
 
(A) ?? . ???? 
(B) ???? 
(C) ?? . ?????? 
(D) ???????? 
Ans: (B) Given: 
• Diode's Voltage Drop, V
d
= 0.5 V 
• Maximum Power Rating, P = 100 mW = 0.1 Watts 
• Battery EMF, E = 1.5 V 
• Resistance = ?? 
1 Finding Current in the Circuit: 
So it's given E = 1.5 V and Vd = 0.5 V 
Formula: P = I
*
???? ? I = (P/Vd) 
I = (0.1/0.5) = 0.2 A 
2 Finding Potential Drop Across ?? 
V = E - Vd = 1.5 - 0.5 = 1 V 
3 Finding Value of ?? 
From above, 
?? = 1?? and ?? = 0.2 A
?? = ?????? = ?? /?? = 1/0.2 = 5 ohms 
 
 
 
Q12: In the following circuits ???? -junction diodes ?? ?? ' ?? ?? and ?? ?? are ideal for the following 
potential of ?? and ?? , the correct increasing order of resistance between ?? and ?? will be 
 
(i) -???? ?? , -?? ?? 
(ii) -?? ?? , -???? ?? 
(iii) -?? ?? , -???? ?? 
(A) (i) < (ii) < (iii) 
(B) (iii) < (ii) < (i) 
(C) (ii) = (iii) < (i) 
(D) (i) = (iii) < (i) 
Ans: (C) (i) 
 
 
 
Q13:  Which is the correct diagram of a half-wave rectifier - 
 
Ans:  (B)