Semiconductor

Question 1

What is energy band

Answer 1

Energy level with continuous energy variation is energy band

Question 2

What is conduction band

Answer 2

Energy band above valence band is called conduction band

Question 3

Define energy band gap

Answer 3

Gap between top of valence band and bottom of conduction band is called energy band gap

Question 4

What is hole

Answer 4

Vacancy with the effective +ve charge is called a hole

Question 5

State properties of intrinsic semiconductors

Answer 5

1 No. of free e- is equal to no of hole
2an intrinsic semiconductor will behave as insulator at T =0K

Question 6

What is the necessity of extrinsic semiconductor

Answer 6

Conductivity of intrinsic semiconductors depends on its temp at room temp it’s conductivity is very low
No important devices can be developed using these semiconductors so their is need of improving their conductivity

Question 7

Define extrinsic semiconductor

Answer 7

Small amount of impurity when added to the pure semiconductor it’s conductivity is increased manifold. Such material are known as extrinsic semiconductor

Question 8

What is doping

Answer 8

Addition of a desirable impurity is called doping

Question 9

What are dopants

Answer 9

The impurity atoms that are added in doping are dopants

Question 10

What is donor impurity

Answer 10

Pentavalent dopant is donating one extra e- for conduction and hence is known as donor impurity

Question 11

Why minority charge carriers can be destroyed

Answer 11

Because of abundance of majority current carriers the minority carriers produced thermally have more chance of meeting majority carriers and thus getting destroyed

Question 12

Although Sn is a group 4 element it is considered as metal . Why ?

Answer 12

Because the energy gap in its case is 0 eV

Question 13

How diffusion current is produced in p-n junction

Answer 13

During the formation of p-n junction due to the concentration gradient across p and n side hole and e- diffuses . This motion of charge carriers gives rise to diffusion current

Question 14

Define depletion region

Answer 14

Space-charge region on either side of junction is known as depletion region

Question 15

What is drift

Answer 15

The motion of charge carriers due to the electric field is called drift

Question 16

How is p-n junction formed

Answer 16

Initially , diffusion current is large and drift current is small . As the diffusion continues the space charge region on either side of the junction extended thus increase in electric field and hence drift current . This process continues until the diffusion current equals the drift current hence a p-n junction is formed

Question 17

What is a diode

Answer 17

P-n junction with metallic contacts at the ends for the application of an external voltage

Question 18

Define forward bias

Answer 18

When an external voltage is applied across a semiconductor diode such that p side is connected to the +ve terminal of the battery and n-side to -ve terminal it is called said to be forward bias

Question 19

What is minority carrier injection

Answer 19

Due to applied voltage e- from n-side cross the depletion region and reach p-side . This process is known as minority carrier injection

Question 20

Define reverse bias

Answer 20

When an external voltage is applied across the diode such that n-side is +ve and p-side is -ve it is said to be reverse biased

Question 21

Define breakdown voltage

Answer 21

Current under reverse bias is essential voltage independently upto a critical reverse bias voltage known as breakdown voltage

Question 22

Define threshold voltage

Answer 22

After the characteristics voltage the diode current increase significantly even for a very small increas in the diode bias voltage . This voltage is called the threshold voltage

Question 23

Define reverse saturation current

Answer 23

For the diode in reverse bias the current is very small and almost remain constant with change in bias . Is is called reverse saturation current

Question 24

What is rectifier

Answer 24

If an alternating voltage is applied across a diode the current flows only I that part of the cycle when the diode is forward biased . This property is used to rectify alternating voltage and the circuit used for this purpose is called a rectifier

Question 25

Define half wave rectifier

Answer 25

If an alternating voltage is applied across a diode in series with a load a pulsating voltage will appear across the load only during the half cycle of the AC input during which the diode is forwards biased sech rectifiers is called half wave rectifire

Question 26

Define full wave rectifier

Answer 26

Circuit using two diodes gives output rectified voltage corresponding to both the +ve as well as -ve half of the AC cycle . Hence it is known as full wave rectifier

Question 27

What is center tap transformer

Answer 27

For a full wave rectifier the secondary of the transformer is provided with a center tapping so it is called centre tap transformer