PN junctions Flashcards
What is a PN junction?
A boundary where P-type and N-type semiconductor materials meet.
Types of junctions: Diffused Junction, Ion Implantation, Grown Junction.
What are majority and minority charge carriers in semiconductors?
Majority carriers: Dominant charge carriers. N-type: Electrons. P-type: Holes.
Minority carriers: Less prevalent charge carriers. N-type: Holes. P-type: Electrons.
How does a PN junction form?
Diffusion: Electrons diffuse from N-type to P-type; holes diffuse from P-type to N-type. Positive ions in N-type and negative ions in P-type are ‘revealed,’ forming a depletion region.
Drift: Drift current arises from carrier movement in response to an electric field. Equilibrium forms between drift and diffusion currents, and energy bands bend.
What is the depletion region in a PN junction?
A region near the PN junction where ions are ‘revealed’ due to diffusion of charge carriers. Prevents further carrier movement until equilibrium is reached.
What is the built-in potential barrier in a PN junction?
Energy band bending prevents electrons and holes from crossing the junction. This creates a potential barrier, making the material non-conductive under equilibrium.
What happens to a PN junction under forward bias?
Applied voltage reduces and shifts the potential barrier. Charge carriers recombine, creating current.
What happens to a PN junction under reverse bias?
Reverse voltage increases the potential barrier. Charge carriers find it harder to recombine, resulting in no current flow.
What does the current-voltage characteristic graph of a PN junction show?
Positive voltage (forward bias): Current rises exponentially as carriers recombine. Negative voltage (reverse bias): No current until breakdown occurs.
Shockley diode equation represents the relationship.
What is junction breakdown?
Zener Breakdown: Energy bands stretch, conduction and valence band gap becomes small. Quantum tunneling allows carrier recombination.
Avalanche Breakdown: Minority carriers gain kinetic energy and create electron-hole pairs, causing a chain reaction (avalanche).
Why are breakdowns in PN junctions useful?
Zener Diode: Used to stabilize voltage. Avalanche Diode: Can multiply current significantly.
