semiconductor2

What is a p-n junction?

A boundary or interface between p-type and n-type semiconductor regions within a single crystal

What processes occur immediately when a p-n junction is formed?

Diffusion of majority carriers across the junction and recombination near the interface

What is the depletion region?

A region near the junction depleted of mobile carriers containing fixed ionized dopant atoms

What creates the built-in potential?

The electric field from fixed ions in the depletion region opposing further diffusion

What is the typical built-in potential for silicon?

About 0.6 to 0.7 volts

Define forward bias.

Applying voltage with p-side positive relative to n-side reducing the barrier and allowing current flow

Define reverse bias.

Applying voltage with n-side positive relative to p-side increasing the barrier and blocking current

What is drift current?

Flow of minority carriers driven by the electric field across the depletion region dominating in reverse bias

What is diffusion current?

Flow of majority carriers driven by concentration gradients dominating in forward bias

What is the Shockley diode equation?

I equals I0 times (exp(qV over kT) minus 1)

What is rectification?

Allowing current to flow easily in one direction but blocking it in the other

What is reverse saturation current?

Small leakage current under reverse bias due to thermally generated minority carriers

What is avalanche breakdown?

High electric field causes impact ionization leading to rapid current increase

What is Zener breakdown?

Quantum tunneling across a narrow depletion region in heavily doped diodes

How does an LED work?

Forward bias causes recombination of electrons and holes emitting photons with energy set by band gap

Why is silicon not used for visible LEDs?

Its indirect band gap causes energy to be released mainly as heat not light

How does a solar cell work?

Photons create electron hole pairs separated by the built-in field producing current

What is junction capacitance?

Capacitance due to charge separation across the depletion region acting like a capacitor

How does depletion width change with reverse bias?

It increases with increasing reverse voltage

How does depletion width change with forward bias?

It decreases reducing the barrier

What determines the turn-on voltage of a diode?

Primarily the band gap energy of the semiconductor

What is the ideal resistance in reverse bias?

Infinite

What is the ideal resistance in forward bias?

Zero

What is minority carrier injection?

Majority carriers cross the junction under forward bias becoming minority carriers before recombining

What is the primary use of a Zener diode?

Providing a stable reference voltage through operation in breakdown

How does doping affect depletion width?

Higher doping results in a narrower depletion region

What happens to Fermi levels when a junction forms?

They align to form a single constant Fermi level

What is diffusion length?

Average distance a minority carrier travels before recombination

In which quadrant does a solar cell deliver power?

Fourth quadrant of the I V curve

What does bias mean?

Applying a DC voltage to set operating conditions

Calculate conductivity of intrinsic silicon given mobilities and concentration.

Sigma equals e times ni times (mue plus muh) giving about 3.12 times 10 to the minus 4 per ohm metre

What happens to the Fermi level in n-type silicon at high temperature?

It moves toward the intrinsic level as intrinsic carriers dominate