Semiconductor Electronics

Question 1

What happens to covalent bond when temp is high?

Answer 1

Bond breaks, & e’ go to conduction band

Question 2

What happens to intrinsic semiconductor at 0K?

Answer 2

It behaves as insulator

Question 3

What is intrinsically created e’s?

Answer 3

e’s due to breaking of covalent bond

Question 4

Types of extrinsic semiconductors

Answer 4

p & n type

Question 5

When is a semiconductor extrinsic?

Answer 5

When impurities are added and conductivity is increased

Question 6

n type of impurities

Answer 6

pentavalent

Question 7

pentavalent is also called

Answer 7

donors

Question 8

p type of impurities

Answer 8

trivalent

Question 9

metal have _____ resistivity

Answer 9

low

Question 10

semiconductors have _____ resistivity

Answer 10

intermediate to metals & insulators

Question 11

Elemental semiconductors

Answer 11

Silicon & Germanium

Question 12

Valence band

Answer 12

Band which includes the energy levels of the valence electrons

Question 13

conduction band

Answer 13

Band above valence band

Question 14

In intrinsic semiconductors, the number of free
electrons, ne is __________ the number of holes, nh

Answer 14

equal to

Question 15

Doping

Answer 15

Addition of impurities

Question 16

Dopants

Answer 16

Impurity atoms

Question 17

2 things before formation of P N junc diode?

Answer 17

Diffusion & drifting

Question 18

In diffusion, e’ moves from

Answer 18

n to p

Question 19

In drifting, e’s move from

Answer 19

p to n

Question 20

Diffusion current & drifting current are always

Answer 20

opposite

Question 21

Depletion region?

Answer 21

Space-charge region on either side of the junction together

Question 22

What happens due to +ve space-charge region on n side and -ve space-charge on p-side?

Answer 22

electric field directed from positive charge towards negative charge develops

Question 23

What is drifting?

Answer 23

The motion of minority charge
carriers due to the electric field

Question 24

As the diffusion process continues, the space-charge regions on either side

Answer 24

increases

Question 25

When space charge region increase, EF & drift current

Answer 25

increases

Question 26

In a p-n junction under equilibrium there is _____ net current

Answer 26

no

Question 27

Barrier potential

Answer 27

Potential that tends to prevent the movement of e' from the n to p

Question 28

In forward bias, as applied voltage increases

Answer 28

depletion width and effective barrier decreases

Question 29

When applied voltage is less, barrier potential and current

Answer 29

reduces slightly below eq. level; will be less

Question 30

Minority carrier injection

Answer 30

e' from n-side cross depletion region reach p side where they are minority

Question 31

In reverse bias, barrier potential & effective barrier value

Answer 31

increases

Question 32

In reverse bias, diffusion current

Answer 32

decreases

Question 33

Diode reverse current is not very much dependent on

Answer 33

applied voltage

Question 34

threshold voltage

Answer 34

Voltage at which current starts increases

Question 35

threshold voltage for Si

Answer 35

0.7V

Question 36

threshold voltage for Ge

Answer 36

0.2V

Question 37

Reverse saturation current

Answer 37

Current which remains const with change in bias

Question 38

Rectification?

Answer 38

Conversion of AC to DC

Question 39

Types of rectifiers

Answer 39

Full & half wave recifiers

Question 40

When only will a diode conduct?

Answer 40

In forward bias

Question 41

Why can't Ge & Si be used to make LEDs

Answer 41

Their energy gap is very less

Question 42

Colour of LED is due to

Answer 42

energy gap

Question 43

2 Types of transistors

Answer 43

npn & pnp

Question 44

BJT full form

Answer 44

Bipolar Junction Transistor

Question 45

Which is an efficient circuit for getting rectified voltage?

Answer 45

full wave rectifier

Question 46

Rectified voltage is _____ direcitonal

Answer 46

Uni

Question 47

How to get a steady DC output?

Answer 47

Capacitor/Inductor is connected across the output terminals || to load

Question 48

What are filters?

Answer 48

Those filter out the ac ripple and give a pure dc voltage

Question 49

What happens when voltage across capacitor increases?

Answer 49

Rectifier gets charged

Question 50

Why should large capacitors be used?

Answer 50

To make the time constant large, value of C should be large

Question 51

What is used to make LEDs?

Answer 51

GaAs

Question 52

Use of LEDs?

Answer 52

Remote controls, burglar alarm systems, optical communication

Question 53

LED vs incandescent low power lamps:

Answer 53

Low operational voltage & less power. Fast action and no warm-up time required Long life and ruggedness Fast on-off switching capability