3.2 p-n Junctions Flashcards
What is an n-type semiconductor?
When a valency five atom is added and most of the conduction is done by free moving electrons
What is a p-type semiconductor?
When a valency three atom is added where an electron is missing and conduction happens by the movement of positive holes
What is a p-n junction?
A semiconductor grown half n-type and half p-type
How do p-n junctions work?
Electrons diffuse across the depletion layer and combine with positive holes and a potential difference is created as the depletion layer grows
In which bias will a diode conduct and why?
Forward bias, negative to n-type
The electrons will be given enough energy from the battery to overcome the depletion layer
What happens if a diode is connected in reversed bias?
The depletion layer increases as charge carriers are attracted away from the depletion layer
How does an LED work?
When connected in forward bias, electrons and positive holes pass through the junction in opposite directions, and when the holes and electrons combine a photon if radiation is emitted
What determines the colour of the LED?
The type of semiconductor and the distance between the valence and the conduction band
What is the photovoltaic mode?
When photons are incident on the junction and have their energy absorbed, freeing electrons and creating electron-hole pairs which generates a voltage
What is a use of photovoltaic mode?
Solar cells
What is photoconductive mode?
Connected in reverse bias therefore won’t conduct but when photons of light shine on the junction, electrons are freed and create electron-hole pairs which means there is a number of free charge carries in the depletion layer, decreasing the resistance
