Electricity 6 Flashcards
What is doping
When impurities are added to a silicon crystal
What does doping do
changes the electrical properties of the martial (like Lowering its resistance)
What does lowering the resistance do
Increase conductivity
What does it mean when silicon is doped with a group 5 element
N-type semiconductor is produced as there is an available free electron and because the majority charge carrier is an electron the semiconductor is called an n-type
What is the overall charge of a semiconductor and why
It is neutral because it has the same number of electrons as protons
What does it mean when silicon is doped with a group 3 element
P-type semiconductor is produced this means there is an availed positive hole and electrons can move into this free space because the majority charge carrier is a positive hole the semiconductor is called a p-type
When are p-n junctions made
When p-type and n-type semiconductors are joined together. The free electron from the n-type join with holes from the p-type. This produces an area with no charge carries and it is called the depletion layer
What does forward bias mean
This is when the negative voltage is applied to the n-type and the positive voltage is applied to the p-type. The free electrons and positive holes are forced into the depletion layer and the depletion layer is small
When the depletion layer is small will and how will the diode conduct
It will conduct In the forward bias
What does reverse bias mean
This is when the positive voltage is applied to the n-type and the negative voltage is applied to the p-type and the free electrons and positive holes are pulled further from the depletion layer. This depletion layer is large
When the depletion layer is large will and how will the diode conduct
It wont conduct in the reverse bias
What are LEDs connected in
The forward bias. Electrons in the valence band of the n-type combine with hols in the p-type and a photon of light is released in the process
Explain how LEDs work using band theory
1. the electron moves from the valence band of the n-type into the conduction band of the n-type
2. the electron travels from the conduction band of the n-type, across the depletion layer, into the conduction band of the p-type
3. the electron falls from the conduction band of the p-type to the valence band of the p-type
( 1- 3 is explanation for basic p-n junctions )
4. energy released as a photon of light
What are solar cells
Solar cells work like LEDs in reverse , light falls in the depletion layer this gives electrons enough energy to split from the holes and the separated electrons and holes create a potential difference , which generate a small current
