Xagaas 1 x aalas al025ga 075 as lattice spacing a

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Unformatted text preview: r Next Lecture 3 Final Comments Example: AlxGa1- xAs Define a Unit Cell AlGaAs has a zinc blende lattice The unit cell is FCC with 2 atoms per lattice point The lattice spacing is determined using Vegard's Law (linear interpolation): Al x Ga1− x As Lattice Spacing: aAlGaAs = xaGaAs + (1 − x ) aAlAs Al0.25Ga 0.75 As Lattice Spacing: a = (0.25 )(5.6533) + (0.75 )(5.6605 ) = 5.6587 Angstroms Determine the Number of Lattice Points Per Unit Cell: 4 Calculate the Mass of Each Lattice Point 74.92 g mole g Mass of As: mAsAtom = × = 1.24 × 10 −22 mole 6.02 × 10 23 atoms atom 26.98 ⎞ ⎛ 69.72 ⎞ ⎛ Mass of Al0.25Ga 0.75 : ⎜ 0.25 × + ⎜ 0.75 × = 9.93 × 10 −23 23 ⎟ 23 ⎟ ⎝ 6.02 × 10 ⎠ ⎝ 6.02 × 10 ⎠ g Mass of Each Lattice Point: mLatticePoint = 1.24 × 10 −22 + 9.93 × 10 −23 = 2.23 × 10 −22 Lattice Point Calculate the Density Density = 4 × ( 2.23 × 10 −22 ) g ( 5.6587 × 10 −8 cm ) 3 = 4.9 g cm 3 5 Other Materials? •  Binary Zinc Blende? •  Ternary Zinc Blende? •  Quaternary Zinc Blende? –  InAlGaP versus InGaAsP •  Wurtzite? •  Cau\on: Use Vegard’s law to es\mate proper\es such as lance constant only if a specific reference is not available 6 Other Density Concepts •  Areal...
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