Phys 312 - Assignment 6 - Due 26 Feb 98

1.

(a) Sketch a p-MOSFET of the enhancement type.

(b) Indicate the type and density of carriers in each region.

2.

(a) A current of 1 Ampère flows in an electrolytic cell. In how many seconds will Avogadro's number of electrons pass through the cell?

(b) A plate of area 1m² is to be covered with a 1 $\mu$m layer of Zn by electrolytic deposition, using a current of 1 Ampère. Estimate how long the process will take. Find in tables the density (or the lattice constant) of metallic Zinc, and assume that the Zn atoms are deposited as Zn⁺⁺ ions.

3.

Many night lights and security lamps use a strip of photoconductor to tell when it is dark enough for them to turn on. Design a very simple circuit that will cause a light bulb to turn on in the dark.

4.

Melissinos gives the relation

$$n=\frac{1}{2}(N_{D}-N_{A})+\frac{1}{2}\sqrt{(N_{D}-N_{A})^{2}+4n_{i}^{2}}$$

for the carrier density in n - type semiconductors.

(a) Assuming n_i=10¹⁰ (all densities are in cm^-3), plot n as a function of N_D-N_A in the range from -5n_i to 10n_i. What is the value of n when N_D-N_A=10¹⁵?

(b) With the same assumptions as in (a), find and plot p. What is p when N_D-N_A=10¹⁵?

(c) Make a combined plot showing n and p over the range of N_D-N_A from -10n_i to 10n_i.