lecture_13_chex42

lecture_13_chex42 - and S for common MBE materials...

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Molecular Beam Molecular Beam Epitaxy Epitaxy (MBE) (MBE) ! An evaporation method to bring the atoms to the surface one by one (almost like laying bricks) at very low pressures such that λ mf >>L ! Advantages: ! Precise layer by layer control of epitaxial films and doping ! Not complicated by transport effects ! No gas phase reactions ! Important Issues ! How quickly does the source evaporate? ! What is the deposition rate on the substrate? ! What determines uniformity? ! Growth mode and surface diffusion ! Defects
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Typical MBE Apparatus Typical MBE Apparatus
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Evaporation from a source, Knudsen Cell Evaporation from a source, Knudsen Cell Hertz-Knudsen Equation mkT P m kT kT P v N F v v e π 2 8 4 1 4 = = > < = P v = vapor pressure at source T = s A s e eT dA F F n n φθ source receiver θ φ cos cos r S F r eT D 2 = Sticking probability
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T dependence of T dependence of P P v and S for common MBE materials
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Unformatted text preview: and S for common MBE materials Deposition Uniformity Deposition Uniformity φ θ r L θ=φ Centerline deposition rate 2 L S F r eT Do π = d @ d 2 2 2 2 2 d L r and d L L cos + = + = φ 2 2 2 2 2 + + = d L L ) d L ( S F ) d ( r eT D 2 2 2 + = d L L S F ) d ( r eT D ~ let l Deposition Uniformity Deposition Uniformity 2 2 2 2 2 1 L ) d L ( L / S F / S F r r U eT eT Do D + = = π 2 2 2 4 ) d L ( L r r U Do D + = = 2 2 1 1 ) ) L / d ( ( r r U Do D + = = Deposition Uniformity Deposition Uniformity " . " L " d wafer " 10 2 2 2 4 = = = ⇒ d/L 1 0.93 0.2 1 → = → Do D r r U L / d as (i.e., as L gets large but also r D decreases...
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This note was uploaded on 12/29/2011 for the course CHE 142 taught by Professor Ceweb during the Fall '09 term at UCSB.

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lecture_13_chex42 - and S for common MBE materials...

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