What is a P-N junction?
The interface formed when n-type and p-type semiconductor materials are joined together.
What is the electrical behavior of n-type material before contact with p-type?
Electrically neutral with many free electrons balanced by fixed positive donor ions and a few free holes.
What is the electrical behavior of p-type material before contact with n-type?
Electrically neutral with many free holes balanced by fixed negative acceptor ions and a few free electrons.
What happens when n-type and p-type materials are brought into contact?
Free electrons move from n-type to p-type, and free holes move from p-type to n-type.
What is this movement of charge carriers across the junction called?
Diffusion.
What is the purpose of diffusion in a P-N junction?
To equalise the potential difference between the two materials and create electrical neutrality.
What is the Depletion Layer in a P-N junction?
The region where free electrons and holes have diffused and canceled out, leaving no free charge carriers.
What is another name for the Depletion Layer?
Dipole Layer.
What causes the Depletion Layer to form?
The movement (diffusion) of electrons and holes across the P-N junction.
What happens within the Depletion Layer in terms of charge?
The n-type region becomes positively charged, and the p-type region becomes negatively charged.
What are these charged areas within the depletion layer called?
Space Charge Regions.
Why is the depletion layer also called a dipole layer?
Because it contains two oppositely charged space charge regions, forming a dipole.
What is the electrical effect of the depletion layer on current flow?
It acts as an insulator and creates a potential barrier, preventing current flow.
What happens when a small voltage is applied across the P-N junction?
Most of the voltage drops across the depletion layer due to its high resistance.
Why do the neutral regions on either side of the depletion layer have low resistance?
Because they still contain free charge carriers (electrons or holes).
How does the P-N junction remain electrically neutral as a whole despite space charge regions?
The space charge regions are equal and opposite, balancing each other out.
What must a P-N junction have to be used in an electrical circuit?
External connection terminals.
How are terminals typically attached to semiconductor material?
By evaporating a thin metal film to form Ohmic Contacts.
What is an Ohmic Contact?
A thin metal film that provides attachment points for external wires.
What is the terminal connected to the p-type material called?
Anode.
What is the terminal connected to the n-type material called?
Cathode.
What is Forward Bias in a P-N junction?
When positive voltage is applied to the p-type and negative to the n-type, allowing current to flow if voltage is high enough.
What initially happens to the depletion layer under forward bias?
It reduces in size but still acts as a potential barrier (insulator).
What happens when the forward voltage becomes large enough across a PN junction?
The depletion layer disappears and current flows across the junction.
