# IMPORTANT SEMICONDUCTOR PHYSICS CONCEPTS

Define and give examples of a: fact, hypothesis, theory (in scientific terminology.)

What is the meaning of ni, the "intrinsic carrier concentration"?  In a given semiconductor, what variable(s) does it depend upon?

If a 5" diameter Si wafer is n-doped to a depth of 50um with 10^15 atoms/cm^3 of phosphorus, what is the total charge on the wafer?  Explain your answer.

Which way (n -> p or p -> n) does "forward" current flow through a pn junction?  Be able to explain your answer in terms of charge flow.

Describe the concentration of conducting (free to move) particles in the depletion layer of a pn junction.

Describe the concentrations of charges in the depletion layer of a pn junction.

How is the "built-in voltage" Vbi related to the "turn-on" voltage of a diode?

Why doesn't current continue to flow across a pn junction when no voltage is applied--why is the depletion layer a finite width?

Upon what variable(s) does the width of the depletion layer depend?

How is a photodiode or solar cell normally biased in a circuit (what direction is the steady-state applied voltage across it, before you shine the light on it)?  In which direction does current flow through a photodiode when light shines on it?  What is a good electrical circuit model of a solar cell?