4.1 Semiconductor Basics

Question 1

Describe the band structure in a semiconductor

Answer 1

Filled valence band and empty conductance band

• Valence band is a negative parabola shape below the positive parabala shape of the conduction band
• Chemical potential is halfway in between

Question 2

How can we obtain a hole in the valence band?

Answer 2

By exciting an electron into the conduction band

Question 3

Define a hole

Answer 3

An empty electron state/ lack of an electron

Question 4

What is a direct gap?

Answer 4

When the maximum of the valence band and the minimum of the conduction band fall under the same value of k

Question 5

What are “light” and “heavy” holes

Answer 5

holes that are easy and hard to move

Question 6

How can you see light and heavy holes on an E-k diagram?

Answer 6

They are the conduction bands with different shapes parabolas with the same maxima

Question 7

What defines an intrinsic semiconductor?

Answer 7

When the number density of electrons in the conduction band IS equal to the number density of holes in the valence band

Question 8

What defines an extrinsic semiconductor?

Answer 8

When the number density of electrons in the conduction band IS NOT equal to the number density of holes in the valence band

Question 9

How do electrons and holes contribute to the conductivity for an intrinsic semiconductor?

Answer 9

They both contribute similarly

Question 10

How do electrons and holes contribute to the conductivity for an extrinsic semiconductor?

Answer 10

Majority carriers dominate

Question 11

Define doping in relation to a semi conductor

Answer 11

Deliberately adding impurities to disrupt the balance between the number of electrons in the conduction band and holes in the valence band forming an extrinsic semiconductor

Question 12

What type of semiconductor does doping form?

Answer 12

Extrinsic

Question 13

What is a donor atom?

Answer 13

Adding a FILLED state in the conduction band (extra electron)
Aka n dopant

Question 14

What is an acceptor atom?

Answer 14

Adding an EMPTY state in the valence band (extra hole)

Aka p dopant

Question 15

Describe the behaviour of the free electron in the n dopant

Answer 15

It is attracted to the single positive charge on the donor nucleus, forming a bound state giving energy levels which form just below the empty conductance band, raising the chemical potential