3.2 Conductors, Semi-conductors and Insulators

Question 1

What is a conductor?

Answer 1

Material with many free electrons allowing current to flow through it
e.g. metals, semi-metals

Question 2

What is a semi-conductor?

Answer 2

A material that when pure doesn’t conduct but with an impurity added or an increased temperature, allows some conduction to take place
e.g. silicon, geranium, selenium

Question 3

What is an insulator?

Answer 3

Materials with no free electrons and do not conduct

e.g. plastic, glass and wood

Question 4

Describe a conductor in terms of band theory

Answer 4

The highest occupied energy band is the conduction band and is partially full allowing electrons to flow easily
The band gap is overlapped

Question 5

Describe an insulator in terms of band theory

Answer 5

The highest occupied energy band is the valence band and it is completely full
The band gap is large
Electrons almost never jump the gap

Question 6

Describe a semi-conductor in terms of band theory

Answer 6

The valence band is completely full but the band gap is small so with enough energy, small amounts of conduction can occur

Question 7

What is an intrinsic semi conductor?

Answer 7

A pure semiconductor, very few electrons to conduct

Question 8

What is an extrinsic semi conductor?

Answer 8

A doped semiconductor

Question 9

What is doping?

Answer 9

Addition of impurity atoms to pure semiconductor to increase conductivity

Question 10

Describe doping with valency numbers

Answer 10

Semiconductors have valency four atoms, adding valency five atoms allows a free electron to move around, adding valency three atoms leaves a positive hole that electrons are attracted to