1.
1/ How does diffusion current depend on the doping concentration? How does the drift
current depend on the doping concentration?
2/ How does the doping concentration affect both diffusion and drift current in
semiconductors?
3/ What processes take place at the p-n junction in a Si diode that lead to the equilibrium?
4/ What processes take place at the p-n junction in a Si diode? Describe how the depletion
region forms and why diffusion currents stop flowing reaching equilibrium?
5/ What phenomena take place at the p-n junction in a Si diode? Describe how the
depletion region forms and identify the two competing processes that result in the
equilibrium?
6/ What happen to the depletion region and the built-in barrier at the p-n junction in a Si
diode when a) forward bias is applied, b) reverse bias is applied?
7/ What is the principle behind the operation of a voltage regulation?
8/ What is the purpose behind using the different models for a Si p-n junction diode?
Solution
1.A semiconductor can be doped with donor atoms and/or acceptor atoms.   o If the
concentration of donor atoms (ND) is greater than the concentration of acceptor atoms (NA),
then the semiconductor material is n?type, because the concentration of electrons (n) is greater
than the concentration of holes (p): n = ND?NA p = ni 2 /n o If NA > ND, then the
semiconductor material is p?type, because p > n: p = NA?ND n = ni 2 /p
2. Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers
(holes and/or electrons). Diffusion current can be in the same or opposite direction of a drift
current, that is formed due to the electric field in the semiconductor. At equilibrium in a p