2011_ECE_227A_Homework_Solution2

2011_ECE_227A_Homework_Solution2 - needed to generate...

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2011 ECE227A Homework #2 Solutions
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11. i) bulk material is normally thicker than quantum wells. ii) For quantum wells, carriers are confined in the wells, so the carrier injection efficiency is higher. iii) The density of states are different. Quantum wells have separate energy states, while the energy states of bulk material are quasi-continuous. 12. i) They need to lattice matched to avoid a lot of defects. ii) The cladding material must have a larger bandgap and smaller refraction index at working wavelength, compared to the waveguide material. 13. i) Si has an indirect bandgap, and most of the III-V materials, such as GaN, InP, GaAs, have direct bandgap. For indirect bandgap material, phonons are generally
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Unformatted text preview: needed to generate photons because of the different crystal momentum between conduction band valance band. So their efficiency to generate light is very low. 16. 17. 18. 20 wells, because of the energy states splitting. ( Assuming the wave function of the first well can still affect the 10 th well.) 19. Since the electrons in InGaAsP material has quite high mobility and they tend to escape from the quantum at high temperature, decreasing the injection efficiency. To improve the performance of laser at higher temperature, the electron leakage current can be decreased by increasing the conduction band offset....
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This note was uploaded on 11/24/2011 for the course ECE 227A taught by Professor Coldren during the Fall '08 term at UCSB.

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2011_ECE_227A_Homework_Solution2 - needed to generate...

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