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Unformatted text preview: MSE 302 Problem Set 2 Solutions (32 Points) 1. (6 Points) a. d o Aug o r d Aug r p p + + = 1 1 1 1 1 1 2 + + = b. The Auger and defect rates will be equal when 3 16 2 10 6 . 8 ... 1 = = cm p p o o Aug d ( **note , this rate coefficient is ~100x too high, so a more realistic p o for the point when the Auger rate dominates would be ~10 18 cm-3) At this dopant concentration, the radiative decay rate is slower than the Auger or defect rates. c. Using the Einstein relation and mobility data for electrons q kT L n n = A t p o =10 15 cm-3 , the defect rate dominates m q s kT Vs m L n 420 10 5 . 4 15 . 5 2 = = A t p o =10 19 cm-3 , the Auger process dominates and s 9 10 3 . 3 m q s kT Vs m L n 93 . 10 3 . 3 01 . 9 2 = = 2. (12 Points) a. Remember that EQE is the number of electrons out of your device divided by the number of photons that strike your device. In part a) we have assumed no reflection or recombination losses and complete absorption so the EQE should be perfect starting from wavelengths equal to the bandgap energy. I have included this EQE curve below. 400 500 600 700 800 900 0.0 0.2 0.4 0.6 0.8 1.0 GaAs EQE at with complete absorption of all photons and no recombination losses EQE Wavelength (nm) b. In part b) we have said that though we still have no reflection and recombination losses, we have a device that is too thin to absorb all of the photons. However, absorption is wavelength dependent as you saw in the graph I provided so that the high energy photons are absorbed better than the low energy photons. Therefore, high energy photons are absorbed better than the low energy photons....
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This note was uploaded on 12/01/2011 for the course MS&E 302 taught by Professor Mcghee during the Spring '08 term at Stanford.
- Spring '08