Semiconductors

Question 1

What is a semiconductor?

Answer 1

A semiconductor is a material that has its conductivity between that of a conductor and a non-conductor (insulator).

Question 2

What is an example of a compound that is a semiconductor?

Answer 2

Gallium arsenide.

Question 3

What is an example of elements that are semiconductors?

Answer 3

Silicon and germanium.

Question 4

What is a Valence band?

Answer 4

Valence band is the series of energy levels that the valence shell of a solid atom exists as.

Question 5

What is a conduction band?

Answer 5

Conduction band is the series of energy levels a valence electron can occupy once it acquires enough energy to jump out of the valence band.

Question 6

What is the energy band gap?

Answer 6

The energy band gap is the difference in energy between the valence band and the conduction band.

Question 7

What is the energy gap?

Answer 7

Energy gap is the energy required for an electron to jump from the valence band and into the conduction band.

Question 8

What are conduction electrons?

Answer 8

Conduction electrons are free electrons that have acquired enough energy to vacate the valence bond and jump into the conduction bond.

Question 9

What is a hole?

Answer 9

A hole is the vacancy left by an electron as it jumps from the valence to the conduction band.

Question 10

What is an electron-hole pair?

Answer 10

An electron-hole pair is created for every electron jumping to the conduction band as it leaves a hole behind.

Question 11

What is recombination?

Answer 11

Recombination occurs when a conduction band electron loses energy and falls back a hole in the valence band.

Question 12

What are the types of semiconductors?

Answer 12

1. Intrinsic semiconductors
2. Extrinsic semiconductors

Question 13

What is an intrinsic semiconductor?

Answer 13

These are chemically pure semiconductors made of a single type of elements such as silicon and germanium.

Question 14

What are extrinsic semiconductors?

Answer 14

These are pure semiconductors which have been combined with other types of elements called impurities.

Question 15

What is doping?

Answer 15

Doping is the introduction of impurities into a pure semiconductor.

Question 16

What are the two types of extrinsic semiconductors?

Answer 16

P-type and N-type.

Question 17

What is an N-type semiconductor?

Answer 17

N-type semiconductors are formed when a pentavalent element is used to dope a pure semiconductor.

Question 18

What is a P-type semiconductor?

Answer 18

P-type semiconductors are formed when a trivalent atom is used to dope a pure semiconductor.

Question 19

What is the donor atom?

Answer 19

The pentavalent atom.

Question 20

What is the acceptor atom?

Answer 20

The trivalent atom.

Question 21

What are the differences between intrinsic and extrinsic semiconductors?

Answer 21

1. Intrinsic are pure semiconductors while extrinsic are not.
2. Intrinsic conductivity only depends on temperature while extrinsic depends on temperature and impurity.
3. Intrinsic conductivity is relatively lower than extrinsic’s conductivity.
4. Electron density is equal to hole density in intrinsic but not equal in extrinsic semiconductors.
5. Examples of intrinsic are silicon and germanium, while for extrinsic is silicon doped with aluminium, arsenic, or antimony.

Question 22

Draw the structure of a PNP and an NPN transistor.

Answer 22

Here