Problem 1
A Schottky diode consists of four layers: metal, n semiconductor, n⁺ semiconductor, and metal.

(a) Draw the band diagram of this Schottky diode. Indicate the Schottky barriers in the diagram.

(b) Draw the electric field in the diode.

(c) Why is the n⁺ layer needed?

(d) What determines the height of the Schottky barrier? Is it different at the metal/n and metal n⁺ interfaces?

Problem 2

(a) Consider a JFET. How does the drain current depend on the drain voltage in the linear regime and in the saturation regime?

(b) Draw the depletion regions of this JFET in the linear regime.

(c) Draw the depletion regions of this JFET in the saturation regime.

(d) An n-channel JFET and a p-channel JFET have the same geometry. Which one has a higher transconductance? Why?

Problem 3
Consider a pnp bipolar transistor. Normally transistors are biased in forward active mode but we will consider reverse active bias.

(a) Plot the minority carrier concentration in a pnp bipolar transistor in reverse active mode.

(b) Compare the emitter efficiency and the base transport factor in forward active mode and reverse active mode.

(c) What is punchthrough? Is it more of a problem or less of a problem in reverse active mode? Why?

(d) If the pnp transistor is made from a direct bandgap semiconductor, would more light be generated in forward active mode or reverse active mode? Why?

Problem 4

Make a drawing of a laser diode and describe how it works. Include the metal contacts in the drawing. What determines the frequency that is emitted? Why is there a threshold current? How is it different from an ordinary light emitting diode?