4.1 Semiconductors

Question 1

What is a chemical compound?

Answer 1

A chemical combination of 2 or more elements

Question 2

How many known elements are there?

Answer 2

Over 100

Question 3

What is the smallest part of a compound which retains all of the compounds characteristics called?

Answer 3

A molecule

Question 4

What part of an atom has a negative charge?

Answer 4

An electron

Question 5

What part of an atom has a positive charge?

Answer 5

A proton

Question 6

What is the mass of a proton?

Answer 6

1827 x bigger than an electron

Question 7

What part of an atom has no electric charge?

Answer 7

A neutron

Question 8

What is the principle to predict the number of electrons in a shell?

Answer 8

Pauli’s Principle = 2n ^2

Question 9

What are the major shells of an atom?

Answer 9

K, L, M… etc

Question 10

What can the major electron shells of an atom be divided into?

Answer 10

Sub shells

s, p, d and f

Question 11

What is a valence shell?

Answer 11

The outer shell of an atom

Question 12

What is a valence electron?

Answer 12

An electron in the outer shell of an atom (the valence shell)

Question 13

What is a Quanta?

Answer 13

The definite units required to move electrons from one shell to the next highest shell.

Question 14

What is ionisation?

Answer 14

When an atom gains/loses electrons

Question 15

What is a negative ion?

Answer 15

An atom that has gained electrons

Question 16

What is a positive ion?

Answer 16

An atom that has lost electrons

Question 17

What is the forbidden band?

Answer 17

An energy gap between the conduction band and the valence band where there are no electrons.

Question 18

What is the conduction band?

Answer 18

Electrons in this band are easily removed by the application of external electric fields. Materials with many electrons here act as good conductors.

Question 19

What is an electron-hole pair?

Answer 19

When an electron moves to the conduction band and leaves behind a deficiency/hole in the valence band.

Question 20

What is a covalent bond?

Answer 20

The sharing of valence electrons between two or more atoms. It holds the atoms together in an orderly structure called a crystal.

Question 21

Pure silicon and germanium are what?

Answer 21

Poor conductors of electricity, but classed as semiconductors.

Question 22

What is the electron current flow?

Answer 22

The movement of electrons in a crystal towards an applied voltage.

Question 23

What charge does the hole in the valence shell have when an electron moves to the conduction band?

Answer 23

A positive charge.

Question 24

What is the hole flow?

Answer 24

The hole in the valence shell moving towards a negative potential (opposite direction of electron flow).

Question 25

What are intrinsic semiconductors?

Answer 25

Semiconductors with no impurities.

Question 26

What is special about the number of holes in an electron-hole pair of an intrinsic semiconductor?

Answer 26

They are always equal to the number of conduction electrons.

Question 27

What periodic table group are most semiconductor materials?

Answer 27

4a

Question 28

What are the groups in the periodic table of which doping materials come from for semiconductors?

Answer 28

3a and 5a

Question 29

What is the ‘favourite’ semiconductor used today?

Answer 29

Silicon (Si) - abundantly available - 8th most common element by mass in the universe

Question 30

What is a tetravalent semiconductor?

Answer 30

A pure or intrinsic semiconductor.

Question 31

What are the two types of doped semiconductor materials?

Answer 31

- N-type | - P-type

Question 32

Why is silicon the semiconductor of choice?

Answer 32

Ease of processing and more stable temperature characteristics

Question 33

What advantage does germanium diodes have over silicon diodes?

Answer 33

Intrinsically low voltage drop, 0.3V meaning low power loss and more efficient diode. Better in signal detection/FM frequencies and low-level digital circuits.

Question 34

What is the average voltage drop on a silicon diode?

Answer 34

0.7V typically,