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:
Depletion region will grow until the electric field from
ions causes electrons and holes to drift in the opposite
direction.
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.
