Problem 1
(a) How is the depletion width of a pn-junction related to the doping?

(b) How can the depletion width be measured experimentally?

(c) What is the built-in voltage $V_{bi}$ of a pn-junction?

(d) What is avalanche breakdown?

Problem 2
(a) Draw a p-channel MESFET showing the source, drain, and gate. Why is there no body contact?

(b) Draw the band diagram (valence band, conduction band) perpendicular to the gate-semiconductor interface.

(c) Why is a MESFET a fast transistor? What can be done to increase the speed of a MESFET?

Problem 3
Draw the charge density $\rho$ and the electric field as a function of position along a line from the metal gate to the substrate for a MOS capacitor in inversion with a p-type substrate.

Problem 4
Describe how a semiconductor laser diode works. What determines the frequency that is emitted? Why is there a threshold current? How is it different from an ordinary light emitting diode?