Problem 1
Ga2O3 is considered a potential semiconductor for high temperature and high power applications. The band structure is shown below.
The band structure of β-Ga2O3, taken from Peelaers, Hartwin, and Chris G. Van de Walle. "Brillouin zone and band structure of β-Ga2O3." physica status solidi (b) 252.4 (2015): 828-832.
(a) Why would this material be good for high temperature operation?
(b) Can you say something about the effective mass of the electrons and holes in Ga2O3?
(c) Discuss whether this material could be used to make light emitting diodes or solar cells.
Problem 2
(a) A pn-diode is heavily doped on the p-side and lightly doped on the n-side. Draw the band diagram of a this diode in reverse bias.
(b) Draw the concentration of holes and electrons as a function of position.
(c) How could you determine the concentration of the minority electrons on the p-side?
(d) In reverse bias, which direction does the drift current flow and which direction does the diffusion current flow? (p to n or n to p?)
Problem 3
(a) Draw a cross section of an n-channel JFET biased in the linear regime. Include the depletion region in the drawing.
(b) Put + and - signs in the drawing to indicate where the positive and negative charge is located.
(c) Where is the highest electric field in the JFET and which way is it pointing?
(d) If you shine light on the JFET, how will this affect the gate current and the drain current?
Problem 4
(a) In a bipolar transistor explain how the gain factor $\alpha$ depends on the emitter efficiency and the base transport factor.
(b) The gain factor $\alpha$ of a bipolar transistor is measured in forward active mode and reverse active mode. What can you say about the emitter efficiency and the base transport factor from this measurement?
(c) What is the difference in the Early effect in forward active and reverse active modes?
Quantity | Symbol | Value | Units | |
| electron charge | e | 1.60217733 × 10-19 | C | |
| speed of light | c | 2.99792458 × 108 | m/s | |
| Planck's constant | h | 6.6260755 × 10-34 | J s | |
| reduced Planck's constant | $\hbar$ | 1.05457266 × 10-34 | J s | |
| Boltzmann's constant | kB | 1.380658 × 10-23 | J/K | |
| electron mass | me | 9.1093897 × 10-31 | kg | |
| Stefan-Boltzmann constant | σ | 5.67051 × 10-8 | W m-2 K-4 | |
| Bohr radius | a0 | 0.529177249 × 10-10 | m | |
| atomic mass constant | mu | 1.6605402 × 10-27 | kg | |
| permeability of vacuum | μ0 | 4π × 10-7 | N A-2 | |
| permittivity of vacuum | ε0 | 8.854187817 × 10-12 | F m-1 | |
| Avogado's constant | NA | 6.0221367 × 1023 | mol-1 |