1.For AlxGa1-xAs, find the composition with energy band gap 2 eV. Also find the effective mass at the Γ, X and the L valleys.

Use AlxGa1-xAs = 1.42 + 1.247x.

Effective mass at Γ valley is 0.067 + 0.083x; the X valley is 0.32 – 0.06x, and the L valley is 0.11 +0.03x, all in units of m*/m0

2. Consider a quantum box of GaAs of dimensions L x L x L. Assume infinite potential barriers and calculate the separation of the ground and the excited energy states as a function of L. If a separation of kBT is needed to observe the confinement effects, what is the maximum size of the L required to see these effects at 4K and at 300K.

3. A sample of GaAs has a free electron density of 1017 cm-3. Calculate the position of the Fermi level using the Boltzmann approximation and the Joyce Dixon approximation at 300K.

4. The absorption coefficients near the band edges of GaAs and Si are 104 cm-1 and 103 cm-1 respectively. What is the minimum thickness of a sample in each case that can absorb 90% of the incident light?

5. Consider a GaAs pn junction diode at T = 300 K with parameters Nd = 8 x 1016 cm-3, Na = 2 x 1015 cm-3, Dn = 207 cm2/s, Dp = 9.80 cm2/s, and τ0 = τp0 =τn0 = 5 x 10-8 s. (a) Calculate the ideal reverse-biased saturation current density. (b) Find the reverse-biased generation current density if the diode is reverse biased at VR = 5 V. (c) Determine the ratio of J gen to Jsat.

6. Derive the density of states of 3D, 2D and 1D systems

7. Describe each of the following devices: solar cells, detectors, LEDs and lasers. Describe their similarities and differences.

8. Choose a specific type of a detector or a laser. You just need to pick one. Decide which material system you will use to design your device and why. Sketch a design of the device and describe its operation as well as the pros and cons of your device.

9. Describe a MODFET or a HEMT. Discuss why this is a superior system. Decide which material system you will use to design your device and why. Sketch a design of the device and describe its operation as well as the pros and cons of your device. What are the design issues you need to consider?

10. Pick a device based on quantum mechanical concepts where the wave nature of the electrons or their spins are important. Describe its fabrication and its operation. Discuss the pros and cons of such a device and its possible application. For this question you should look beyond what we covered in class and look at research papers or other books.

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