Problem 1

(a) Draw the band diagram of an unbiased pn-junction (conduction band, valence band, Fermi energy). Indicate the built-in voltage in the diagram.

(b) How could the built-in voltage be measured?

(c) The depletion width is determined by a balance between drift and diffusion. Describe this balance. Explain why the depletion width changes as the diode is heated up.

Problem 2

(a) Describe diffusion in semiconductor devices. Give examples of how diffusion plays a role in the operation of various devices.

(b) Describe thermionic emission in semiconductor devices. Give examples of how thermionic emission plays a role in the operation of various devices.

(c) Describe tunneling in semiconductor devices. Give examples of how tunneling plays a role in the operation of various devices.

Problem 3
Silicon is an indirect band gap semiconductor and it is not suitable for making light emitting diodes. Nevertheless, some small amount of light is emitted when a silicon pn-junction is forward biased. In this case, both a photon and a phonon are emitted so that energy and momentum are conserved. By causing devices to light up, you can see where they are located on a chip. How would you bias an n-channel MOSFET, a p-channel JFET, and a pnp bipolar transistor to get them to light up?

Problem 4
The first transistor had a metal emitter, a semiconductor base, and a metal collector. Discuss how using metals for the emitter and collector would affect the transistor properties. In your discussion you could include the emitter efficiency, the base transport factor, interface states, the Early effect, majority and minority carrier transport, and punchthrough.