Time: Wednesdays, 16:30. Venue: 5-31

- Optical properties
- Calculate the Brewster angle for an air/ZnO surface for green light.
(
*n*_{ZnO}=2.2) - Calculate the exciton binding energy (within the effective mass theory)
for GaN.
(
*m*_{eff}^{e}=0.2,*m*_{eff}^{h}=0.8, ε=10) - Defects and Doping
- Calculate the temperature-dependence of the hole density in a non-degenerate
*p*-type semiconductor with no compensating donors. The acceptor concentration is 3x10^{16}cm^{-3}, N_{v}=10^{18}cm^{-3}. What is the energetic position of the Fermi level at 0K?

- Diodes
- Read up Schottky's approach to calculate the capacitance of Schottky diodes
(for instance Sze
Physics of semiconductor devices ). - Calculate the potential distribution in a space charge region. The semiconductor
shall be ZnO,
*m*_{eff}^{e}=0.27, ε=8.2. The potential at the interface shall be 2V and the net doping density is 10^{16}cm^{-3}. What is the space charge region width? - Space Charge Spectroscopy
- Solve the differential equation for the time evolution of the probability to find
an electronic defect state occupied. The state shall initially be totally occupied, q(0)=1,
and relaxes into an equilibrium occupancy q(∞), whereas
*e*_{n}=100*c*_{n}. What is*q*(∞)? Assume that the state does not interact with the valence band. - Solar Cells
- Determine the fill factor for the I-V characteristics of the solar cell given on the handout.
- Find out, what the difference (optimisation!) between a solar cell and a photodetector is? Literature: Sze.
- Light Emitting Diodes
- A blue InGaN LED is to be connected to a DC voltage of 12V. Which built-in voltage is to be expected (approximate value)? Calculate the nescessary series resistance if the current through the diode is 10mA!
- Calculate the opening angle of the cone under which light from an AlGaAs/GaAs/AlGas heterostructure
LED (GaAs is the active layer) can be coupled out of the device! (
*n*_{AlGaAs}=3.5)

Hint: Fresnel formula. - Read up about how to make white LEDs!
- Calculate the luminous flux of the sun!
- Solid State Lasers
- What is a Bragg mirror?
- Why are (at least) three electronic states needed to achieve lasing?
- A GaAs laser has an optical power of 1mW and is focussed on a spot of 1mm diametre. Calculate the photon flux!
- A AlGaAs/GaAs VCSEL has GaAs/AlAs Bragg mirrors. The refractive indices of the materials at the laser mode are
*n*_{GaAs}=3.538 and*n*_{AlAs}=2.958. Approximately which wavelength is the laser mode? How thick are the GaAs and AlAs layers? - Transistors
- Read up about the field effect transistor (FET). Compare the FET with a vacuum tube triode.
- CMOS
- Design a XOR gate. Use exclusively NAND gates!