4.3 Semiconductor Applications

Question 1

Describe how a solar cell works

Answer 1

When light is applied to a pn junction, an electron hole pair is created if the energy of the photon is > than the energy gain
- The electron and the hole are then sat in an electrostatic potential, which then causes them to move in opposite directions meaning a current flows

Question 2

How do we build a diode?

Answer 2

By applying a bias across a pn junction

- The pd allows the current to flow in a preferred direction

Question 3

What are two uses of transistors?

Answer 3

Amplification of and switching of electronic signals

Question 4

What is a MOSFET

Answer 4

Metal Oxide Semiconductor Field Effect Transistor

Question 5

Describe crystal growth

Answer 5

• Start with a seed crystal
• Use heating to form a full crystal
• Slice into wafer, clean, cut into chips

Question 6

What are the four methods of growing a semiconductor?

Answer 6

Crystal growth
Epitaxial growth
Deposition
Doping

Question 7

Describe epitaxial growth

Answer 7

• Layer a material onto a substrate
• Wafer acts as a seed to control growth orientation
• Want lattice constants <0.1% different
  Use vapour phase/liquid phase/ molecular beam epitaxy(MBE)

Question 8

When is deposition used?

Answer 8

For other components e.g metal, films, oxides etc

Used in chemical vapour deposition

Question 9

Describe doping in terms of crystal growth

Answer 9

Uses diffusion - Heat a material in the gas of the dopant which creates a concentration gradient
Ion implantation - fire high energy ionised dopant atoms at the surface. Depth is proportional to V used to accelerate