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EECS 232 Lightwave Devices -- Fall 2005
Professor Ming C. Wu
University of California, Berkeley
Dept. Electrical Engineering & Computer Sciences

 
  • Related to HW#1
    • (9/30/2005) In 1(c), why is there no state with (m,n,l) = (2,2,2)? 
      • Answer: (2,2,2) is a quantum state. The solution only includes the first four states. Other (m,n,l) with integer m, n, and l are all states of the quantum box.
  • Related to HW#2
    • (9/30/2005) In 1(b), why is the photon flux the same for in air or semiconductor?
      • Answer: The problem assumes the output mirror of the laser is anti-reflection (AR)-coated. For power density in the laser cavity P (in W/cm^2), reflectivity R ~ 0, the output power density in air is P*(1-R) ~ P. Photon flux is simply P/(hv), and photon energy hv is the same for photons in and outside laser cavity, so the photon fluxes are almos the same.
    • (9/30/2005) For question 2, would you please explain how to get the lineshape function?  Does it depend on the semiconductor?
      • Answer: The lineshape of most semiconductors can be approximated by Lorentzian.
    • (9/30/2005) In 2(d), you divided 2 h_bar by 10^-13 for the lineshape function?  Where does this come from? 
      • Answer: The full width of the Lorentzian lineshape, GAMMA, is related to the intraband relaxation time, t_in: GAMMA = 2 * h_bar / t_in. Here, I used a typical value (0.1 ps) for t_in. The corresponding width of the Lorentzian lineshape is ~ 13 meV. Of course, if you assume a different value for GAMMA or t_in, you will obtain a different numerical answer.
  • Related to HW#3:
    • (10/4/2005) For all of the problems is it okay for us to assume zero linewidth to simplify calculations?  If not, do we assume a constant gamma function was done in HW3 solutions?
      • Answer: Yes. Unless explicitly stated, you can assume zero linewidth (i.e., delta function for energy conservation) for HW and exam problems. There are some exceptions. In quantum box problem, such as the one in HW#2, you need to use Lorentzian lineshape function to get a realistic absorption coefficient (otherwise, it becames infinity).      
    • (10/4/2005): For problem 9.9b), how do we determine the crossover point for Fc-Fv without knowing carrier concentrations or Fermi-Levels?  Do we assume the same carrier concentrations as the previous problem (9.7)?
      • Answer: The problem did not mention any electron/hole concentration. So you can assume the semiconductor is unbiased (i.e., all electrons are in the valance band).