211A_W11_Homework_3

211A_W11_Homework_3 - ECE/MAT 211A: Homework 3. Due January...

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1 ECE/MAT 211A: Homework 3. Due January 26, 2011, at noon. Problem 1: Vibrational frequencies of silicon-hydrogen bonds All CMOS transistors contain an interface between silicon and SiO 2. Because of the difference in crystal structure between Si and SiO 2 , a few Si atoms at the interface end up being less than fourfold coordinated. This would lead to an electronic defect that can trap carriers and would be detrimental to the device. Fortunately, hydrogen can be used to “passivate” such defects: hydrogen forms a strong bond with the “undercoordinated” silicon atoms, and eliminates the defect. The presence of such silicon-hydrogen bonds can be detected and monitored with vibrational spectroscopy. The experiment consists of shining monochromatic (laser) light on the sample, and monitoring the absorption. Such experiments show that there is strong absorption around 2000 cm -1 (see note below for units). A simple harmonic oscillator is often a very good model for analyzing vibrational modes; let’s apply it to a
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211A_W11_Homework_3 - ECE/MAT 211A: Homework 3. Due January...

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