LEC2p - MS415 Crystal Properties Crystal Lattices: Periodic...

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MS415 Lec. 2 1 Crystal Properties • Crystal Lattices: Periodic arrangement of atoms Repeated unit cells (solid-state) Stuffing atoms into unit cells Determine mechanical & electrical properties polycrystalline amorphous crystalline N O ZnO GaN High performance, high current
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MS415 Lec. 2 The simplest structural unit is the unit cell . There may be several different shapes of the combination of the circles, however, there is only one which is the basic. The basic →Unit Cell Crystal Structure The lattice parameters a, b, and c are unit cell lengths. The lattice parameters α, β , and γ are angles between adjacent unit-cell axes The periodic lattice:
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MS415 Lec. 2 First, there are only seven unique unit-cell shape that can be stacked together to fill three-dimensional space. These are called Seven Crystal Systems. Seven Crystal Systems & Fundamental crystal geometry has the seven crystal systems and 14 crystal lattices. (Reference)
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MS415 Lec. 2 (14 possible way of arrangement of the lattice points in unit-cells.) Second, consider the points where the atoms are stacked in a given unit-cell. These points are called lattice points . And there is 14 possible ways of arrangement of the lattice points, called 14 Bravais’ Lattices . (Reference) Fourteen Bravais Lattices
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MS415 Lec. 2 5 The Silicon lattice: • Si atom: 14 electrons occupying the lowest 3 energy levels: –1s, 2s, 2p orbitals filled by 10 electrons – 3s, 3p orbitals filled by 4 electrons • Each Si atom has four neighbors • “Diamond lattice” : Two fcc structures • How many atoms per unit cell? • Ge is also diamond structure Zinc blende lattice • GaAs, AlAs, InP • Two intercalated fcc lattices Wurtzite lattice • GaN, CdS, ZnS
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MS415 Lec. 2 6 Crystallographic planes and Si wafers Si wafers usually cut along {100} plane with a notch or flat side to orient the wafer during fabrication 0
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This note was uploaded on 05/16/2010 for the course MSE MSE415 taught by Professor Lee during the Spring '10 term at 카이스트, 한국과학기술원.

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LEC2p - MS415 Crystal Properties Crystal Lattices: Periodic...

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