Semiconductor - PPT - Class 12 PDF Download

 Page 1


SEMICONDUCTOR DEVICES 
            
1.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor    - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator  - 6 ev (or) more than 6 ev. 
2. Zener effect and avalanche  effect  are the two possible  break down 
mechanisms  that helps the external current . Why 
Zener effect : The electric field in the depletion  layer reach a point that it can 
break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that  across the depletion layer 
under the influence of the electric field gain sufficient kinetic energy to be able to 
break covalent bond in atoms which they collide. 
 
3. Light emission in semiconductor is the process of creation of a photon by 
means of the annihilation of an electron-hole pair. How can we create them. Give 
the necessary  condition for the light emission? 
   h? = E
eh
  greater than or equal to E
g. 
      Condition for light emission is  excess carriers. 
 
 
4.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor  is heated more & more electrons get enough energy to 
jump across  the forbidden energy gap from valence band to the conduction 
band, where they are free to conduct electricity. Thereby increasing the 
conductivity of a semi conductor. 
 
5. On the basis of energy  level diagram,  identify the  P-type semi conductor &  
N-type semi conductor  
 
   C.B 
                             _ _ _ _ _ _ _ _ _ _ _ 
                            
 
    V.B 
 
.  
 
   C.B 
                               
      _ _ _ _ _ _ _ _ _ _ _ _ 
      
    V.B 
 
Donor  energy level 
Acceptor  energy level 
Page 2


SEMICONDUCTOR DEVICES 
            
1.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor    - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator  - 6 ev (or) more than 6 ev. 
2. Zener effect and avalanche  effect  are the two possible  break down 
mechanisms  that helps the external current . Why 
Zener effect : The electric field in the depletion  layer reach a point that it can 
break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that  across the depletion layer 
under the influence of the electric field gain sufficient kinetic energy to be able to 
break covalent bond in atoms which they collide. 
 
3. Light emission in semiconductor is the process of creation of a photon by 
means of the annihilation of an electron-hole pair. How can we create them. Give 
the necessary  condition for the light emission? 
   h? = E
eh
  greater than or equal to E
g. 
      Condition for light emission is  excess carriers. 
 
 
4.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor  is heated more & more electrons get enough energy to 
jump across  the forbidden energy gap from valence band to the conduction 
band, where they are free to conduct electricity. Thereby increasing the 
conductivity of a semi conductor. 
 
5. On the basis of energy  level diagram,  identify the  P-type semi conductor &  
N-type semi conductor  
 
   C.B 
                             _ _ _ _ _ _ _ _ _ _ _ 
                            
 
    V.B 
 
.  
 
   C.B 
                               
      _ _ _ _ _ _ _ _ _ _ _ _ 
      
    V.B 
 
Donor  energy level 
Acceptor  energy level 
6. A student has to study the  characteristics of a P-N Junction diode. What kind 
of a circuit arrangement should she use for this purpose? 
 
 
 
7.   Draw the typical shape of input characteristics likely to be obtainedby a 
student . What do we understand by the forward bias and reverse bias of the 
diode? In which of these states does the diode being used as a rectifier.? 
 
 
 
 
8.  To achieve light amplification, We should provide positive feed back in 
LASER .Why?  
Laser is not an amplifier but an oscillator! However, any oscillator is an amplifier 
with a positive feedback. To obtain lasing , it is necessary to achieve light 
amplification  and provide positive optical feedback. 
 
9. Self supporting stimulated emission is the  principle of a Laser .why? 
 Probability of stimulated emission is proportional to the density of excess 
electrons and holes , and to the density of photons. Under the normal 
circumstances it is negligible. Therefore if  we provide a positive feedback , the 
stimulated emission  can become self supporting. 
 
11. If  the active layer in a P-N photo diode is the thick  depletion layer  then P-N 
Photodiode  act very effective . Why? 
 In p-I-n photodiode ,due to thick  i – layer  the sensitivity  improves 
dramatically.. Large reverse biases (< 100V for  Si ) may be required. 
 
12. Modern technology use poly silicon  instead of metal to form the gate. Why? 
 Poly silicon  has high conductivity  compare to metal.  
 
 
Page 3


SEMICONDUCTOR DEVICES 
            
1.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor    - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator  - 6 ev (or) more than 6 ev. 
2. Zener effect and avalanche  effect  are the two possible  break down 
mechanisms  that helps the external current . Why 
Zener effect : The electric field in the depletion  layer reach a point that it can 
break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that  across the depletion layer 
under the influence of the electric field gain sufficient kinetic energy to be able to 
break covalent bond in atoms which they collide. 
 
3. Light emission in semiconductor is the process of creation of a photon by 
means of the annihilation of an electron-hole pair. How can we create them. Give 
the necessary  condition for the light emission? 
   h? = E
eh
  greater than or equal to E
g. 
      Condition for light emission is  excess carriers. 
 
 
4.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor  is heated more & more electrons get enough energy to 
jump across  the forbidden energy gap from valence band to the conduction 
band, where they are free to conduct electricity. Thereby increasing the 
conductivity of a semi conductor. 
 
5. On the basis of energy  level diagram,  identify the  P-type semi conductor &  
N-type semi conductor  
 
   C.B 
                             _ _ _ _ _ _ _ _ _ _ _ 
                            
 
    V.B 
 
.  
 
   C.B 
                               
      _ _ _ _ _ _ _ _ _ _ _ _ 
      
    V.B 
 
Donor  energy level 
Acceptor  energy level 
6. A student has to study the  characteristics of a P-N Junction diode. What kind 
of a circuit arrangement should she use for this purpose? 
 
 
 
7.   Draw the typical shape of input characteristics likely to be obtainedby a 
student . What do we understand by the forward bias and reverse bias of the 
diode? In which of these states does the diode being used as a rectifier.? 
 
 
 
 
8.  To achieve light amplification, We should provide positive feed back in 
LASER .Why?  
Laser is not an amplifier but an oscillator! However, any oscillator is an amplifier 
with a positive feedback. To obtain lasing , it is necessary to achieve light 
amplification  and provide positive optical feedback. 
 
9. Self supporting stimulated emission is the  principle of a Laser .why? 
 Probability of stimulated emission is proportional to the density of excess 
electrons and holes , and to the density of photons. Under the normal 
circumstances it is negligible. Therefore if  we provide a positive feedback , the 
stimulated emission  can become self supporting. 
 
11. If  the active layer in a P-N photo diode is the thick  depletion layer  then P-N 
Photodiode  act very effective . Why? 
 In p-I-n photodiode ,due to thick  i – layer  the sensitivity  improves 
dramatically.. Large reverse biases (< 100V for  Si ) may be required. 
 
12. Modern technology use poly silicon  instead of metal to form the gate. Why? 
 Poly silicon  has high conductivity  compare to metal.  
 
 
 
15. Digiatal signal is preferred for communication  Why not analog signal?Give 
its waveform.  
A continuous time varying wave form of a current  (or) voltage is called analogue 
signal.  
   
A digital signal in a two level voltage signal (ie) “0” and “1” . Digital signals are in 
the form of pulse of equal level. 
   
 
16. In a given diagram ,is the diode reverse (or) forward biased?. 
  
 
Reverse biased. 
 
17.Identify the logic  gate, Give its truth table and output wave form?. 
  
   
NAND GATE. 
 
18.The ratio of number of free electrons to holes n
e
/n
h
 for two different materials 
A and B are 1 and <1 respectively. Name  the type of semi conductor to which A 
and B belongs. 
If  n
e
/n
h =1 . 
Hence A is intrinsic semi conductor. 
If n
e
/n
h 
<1 , n
e
<n
h  
hence B is P-type. 
 
19.Can you identify waveform. How will  you convert A.C To D.C? 
 
Page 4


SEMICONDUCTOR DEVICES 
            
1.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor    - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator  - 6 ev (or) more than 6 ev. 
2. Zener effect and avalanche  effect  are the two possible  break down 
mechanisms  that helps the external current . Why 
Zener effect : The electric field in the depletion  layer reach a point that it can 
break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that  across the depletion layer 
under the influence of the electric field gain sufficient kinetic energy to be able to 
break covalent bond in atoms which they collide. 
 
3. Light emission in semiconductor is the process of creation of a photon by 
means of the annihilation of an electron-hole pair. How can we create them. Give 
the necessary  condition for the light emission? 
   h? = E
eh
  greater than or equal to E
g. 
      Condition for light emission is  excess carriers. 
 
 
4.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor  is heated more & more electrons get enough energy to 
jump across  the forbidden energy gap from valence band to the conduction 
band, where they are free to conduct electricity. Thereby increasing the 
conductivity of a semi conductor. 
 
5. On the basis of energy  level diagram,  identify the  P-type semi conductor &  
N-type semi conductor  
 
   C.B 
                             _ _ _ _ _ _ _ _ _ _ _ 
                            
 
    V.B 
 
.  
 
   C.B 
                               
      _ _ _ _ _ _ _ _ _ _ _ _ 
      
    V.B 
 
Donor  energy level 
Acceptor  energy level 
6. A student has to study the  characteristics of a P-N Junction diode. What kind 
of a circuit arrangement should she use for this purpose? 
 
 
 
7.   Draw the typical shape of input characteristics likely to be obtainedby a 
student . What do we understand by the forward bias and reverse bias of the 
diode? In which of these states does the diode being used as a rectifier.? 
 
 
 
 
8.  To achieve light amplification, We should provide positive feed back in 
LASER .Why?  
Laser is not an amplifier but an oscillator! However, any oscillator is an amplifier 
with a positive feedback. To obtain lasing , it is necessary to achieve light 
amplification  and provide positive optical feedback. 
 
9. Self supporting stimulated emission is the  principle of a Laser .why? 
 Probability of stimulated emission is proportional to the density of excess 
electrons and holes , and to the density of photons. Under the normal 
circumstances it is negligible. Therefore if  we provide a positive feedback , the 
stimulated emission  can become self supporting. 
 
11. If  the active layer in a P-N photo diode is the thick  depletion layer  then P-N 
Photodiode  act very effective . Why? 
 In p-I-n photodiode ,due to thick  i – layer  the sensitivity  improves 
dramatically.. Large reverse biases (< 100V for  Si ) may be required. 
 
12. Modern technology use poly silicon  instead of metal to form the gate. Why? 
 Poly silicon  has high conductivity  compare to metal.  
 
 
 
15. Digiatal signal is preferred for communication  Why not analog signal?Give 
its waveform.  
A continuous time varying wave form of a current  (or) voltage is called analogue 
signal.  
   
A digital signal in a two level voltage signal (ie) “0” and “1” . Digital signals are in 
the form of pulse of equal level. 
   
 
16. In a given diagram ,is the diode reverse (or) forward biased?. 
  
 
Reverse biased. 
 
17.Identify the logic  gate, Give its truth table and output wave form?. 
  
   
NAND GATE. 
 
18.The ratio of number of free electrons to holes n
e
/n
h
 for two different materials 
A and B are 1 and <1 respectively. Name  the type of semi conductor to which A 
and B belongs. 
If  n
e
/n
h =1 . 
Hence A is intrinsic semi conductor. 
If n
e
/n
h 
<1 , n
e
<n
h  
hence B is P-type. 
 
19.Can you identify waveform. How will  you convert A.C To D.C? 
 
 
 
20. Under what conditions an amplifier can be converted in to an oscillator.Draw 
a suitable diagram . 
 1. When feed back is positive.        2. When feed factor k is equal to l/AV 
 
21.Using basic logic gates (NOT, OR, AND )  construct the circuit for the   given  
logic gate &  give its truth table and wave form.? 
 
22. Convert a Fraction from Decimal (0.625)
10 
 to Binary? 
Hint:(0.625)
10 
=  (0.101)
2 
23. Convert  an octal number (4536) into decimal number? 
(4536)
8
 = 4x8
3
 + 5x8
2 + 
3x8
1 + 
6x8
0 
= (1362)
10
  
24. Convert Hexa decimal (3A9F) and (2D3.5) into decimal number? 
(3A9F)
16
 = 3x16
3
 + 10x16
2 + 
9x16
1 + 
15x16
0 
= 14999
10
  
(2D3.5)
16
 = 2x16
2 + 
13x16
1 + 
3x16
0
 + 5x16
-1 
= 723.3125
10 
 
25. In the circuit  diagram  given , a volt meter  is connected  across  a lamp , 
what  changes would occur at lamp”L” and voltmeter “V:” , if the resistor R  is 
reduce in value? Give reason for your answer? 
Page 5


SEMICONDUCTOR DEVICES 
            
1.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor    - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator  - 6 ev (or) more than 6 ev. 
2. Zener effect and avalanche  effect  are the two possible  break down 
mechanisms  that helps the external current . Why 
Zener effect : The electric field in the depletion  layer reach a point that it can 
break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that  across the depletion layer 
under the influence of the electric field gain sufficient kinetic energy to be able to 
break covalent bond in atoms which they collide. 
 
3. Light emission in semiconductor is the process of creation of a photon by 
means of the annihilation of an electron-hole pair. How can we create them. Give 
the necessary  condition for the light emission? 
   h? = E
eh
  greater than or equal to E
g. 
      Condition for light emission is  excess carriers. 
 
 
4.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor  is heated more & more electrons get enough energy to 
jump across  the forbidden energy gap from valence band to the conduction 
band, where they are free to conduct electricity. Thereby increasing the 
conductivity of a semi conductor. 
 
5. On the basis of energy  level diagram,  identify the  P-type semi conductor &  
N-type semi conductor  
 
   C.B 
                             _ _ _ _ _ _ _ _ _ _ _ 
                            
 
    V.B 
 
.  
 
   C.B 
                               
      _ _ _ _ _ _ _ _ _ _ _ _ 
      
    V.B 
 
Donor  energy level 
Acceptor  energy level 
6. A student has to study the  characteristics of a P-N Junction diode. What kind 
of a circuit arrangement should she use for this purpose? 
 
 
 
7.   Draw the typical shape of input characteristics likely to be obtainedby a 
student . What do we understand by the forward bias and reverse bias of the 
diode? In which of these states does the diode being used as a rectifier.? 
 
 
 
 
8.  To achieve light amplification, We should provide positive feed back in 
LASER .Why?  
Laser is not an amplifier but an oscillator! However, any oscillator is an amplifier 
with a positive feedback. To obtain lasing , it is necessary to achieve light 
amplification  and provide positive optical feedback. 
 
9. Self supporting stimulated emission is the  principle of a Laser .why? 
 Probability of stimulated emission is proportional to the density of excess 
electrons and holes , and to the density of photons. Under the normal 
circumstances it is negligible. Therefore if  we provide a positive feedback , the 
stimulated emission  can become self supporting. 
 
11. If  the active layer in a P-N photo diode is the thick  depletion layer  then P-N 
Photodiode  act very effective . Why? 
 In p-I-n photodiode ,due to thick  i – layer  the sensitivity  improves 
dramatically.. Large reverse biases (< 100V for  Si ) may be required. 
 
12. Modern technology use poly silicon  instead of metal to form the gate. Why? 
 Poly silicon  has high conductivity  compare to metal.  
 
 
 
15. Digiatal signal is preferred for communication  Why not analog signal?Give 
its waveform.  
A continuous time varying wave form of a current  (or) voltage is called analogue 
signal.  
   
A digital signal in a two level voltage signal (ie) “0” and “1” . Digital signals are in 
the form of pulse of equal level. 
   
 
16. In a given diagram ,is the diode reverse (or) forward biased?. 
  
 
Reverse biased. 
 
17.Identify the logic  gate, Give its truth table and output wave form?. 
  
   
NAND GATE. 
 
18.The ratio of number of free electrons to holes n
e
/n
h
 for two different materials 
A and B are 1 and <1 respectively. Name  the type of semi conductor to which A 
and B belongs. 
If  n
e
/n
h =1 . 
Hence A is intrinsic semi conductor. 
If n
e
/n
h 
<1 , n
e
<n
h  
hence B is P-type. 
 
19.Can you identify waveform. How will  you convert A.C To D.C? 
 
 
 
20. Under what conditions an amplifier can be converted in to an oscillator.Draw 
a suitable diagram . 
 1. When feed back is positive.        2. When feed factor k is equal to l/AV 
 
21.Using basic logic gates (NOT, OR, AND )  construct the circuit for the   given  
logic gate &  give its truth table and wave form.? 
 
22. Convert a Fraction from Decimal (0.625)
10 
 to Binary? 
Hint:(0.625)
10 
=  (0.101)
2 
23. Convert  an octal number (4536) into decimal number? 
(4536)
8
 = 4x8
3
 + 5x8
2 + 
3x8
1 + 
6x8
0 
= (1362)
10
  
24. Convert Hexa decimal (3A9F) and (2D3.5) into decimal number? 
(3A9F)
16
 = 3x16
3
 + 10x16
2 + 
9x16
1 + 
15x16
0 
= 14999
10
  
(2D3.5)
16
 = 2x16
2 + 
13x16
1 + 
3x16
0
 + 5x16
-1 
= 723.3125
10 
 
25. In the circuit  diagram  given , a volt meter  is connected  across  a lamp , 
what  changes would occur at lamp”L” and voltmeter “V:” , if the resistor R  is 
reduce in value? Give reason for your answer? 
 
 
In the given circuit  emitter –base junction of N-P-N  transistor  is forward biased 
, with battery “B”. When “r” decreases I
E
  increases . Because   
 I
C
  = I
E 
– I
B
  . 
Therefore  IC will also increase. Hence  bulb will glow with more brightness and 
voltmeter reading will increase.
 
 
 
26.Determine the current through resistance  “R” in each circuit. Diodes D1 and 
D2  are identical and ideal. 
 
 In circuit (i) Both D1 and D2 are forward baiased hence both will conduct 
current  and resistance  of each diode is “0”. .Therefore I = 3/15 = 0.2 A 
(ii) Diode D1 is forward bias and D2 is reverse bias, therefore  resistance D1 is 
“0” and resistance D2 is infinite. Hence  D1  will conduct and D2 do not conduct . 
No current flows in  the circuit. 
 
 
27.Write the output wave form of the OR gate for the inputs given? 
Time 
Interval 
1 2 3 4 5 6 7 8 
Input A 0 1 1 0 0 1 1 0