Introduction to the Physics of Semiconductor Devices
Seminar series held at the University of Pretoria by Matthias Schmidt in 2012.
Time: Wednesdays, 16:30. Venue: 5-31
Part 1: Semiconductor Properties
Part 2: Semiconductor Devices
- Optical properties
- Calculate the Brewster angle for an air/ZnO surface for green light.
- Calculate the exciton binding energy (within the effective mass theory)
- 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 3x1016cm-3, Nv=1018cm-3.
What is the energetic position of the Fermi level at 0K?
- 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, meffe=0.27, ε=8.2.
The potential at the interface shall be 2V and the net doping density is
1016cm-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 en=100cn.
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! (nAlGaAs=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
nGaAs=3.538 and nAlAs=2.958. Approximately which wavelength is the
laser mode? How thick are the GaAs and AlAs layers?
- Read up about the field effect transistor (FET). Compare the FET with a vacuum tube triode.
- Design a XOR gate. Use exclusively NAND gates!