Solid State Electronics EC 210 – EC 211 Prof.Dr. Iman Gamal Eldin Morsi 1

Crystal Structures Galena is lead sulfide, PbS, and has a cubic crystal structure |SOURCE: Photo by SOK Cubic FeS 2, iron sulfide, or pyrite, crystals. The crystals look brass-like yellow (“fool’s gold”). |SOURCE: Photo by SOK

Chapter 1 : Crystal Structure 3

Crystalline atoms pack in periodic, 3D arrays typical of: -metals -many ceramics -some polymers Noncrystalline (amorphous) atoms have no periodic packing occurs for: -complex structures -rapid cooling Classification of solids according to the arrangement of atoms: 4

Lattice- an in definitely extended arrangement of points each of which is surrounded by an identical grouping of neighboring point Unit cell - smallest region that completely describes the pattern Lattice and Unit cell: 5

Types of Unit Cell 6

Types of Cubic Unit Cell: Crystals with same type of atom: Crystals with same type of atom: Simple Cubic (SC) Body-Centered Cubic (BCC) Face-Center Cubic (FCC) Diamond unit cell Crystals with multiple atoms: Crystals with multiple atoms: Zinc Blend unit cell NACl unit cell 7

Simple Cubic (SC) 1 unit cell contains: 8 x 1/8 =1 atom/unit cell. a:lattice parameter R: atomic radius a=2R a=2R 8

Body Centered Cubic (BCC) 1/8 atom at each corner 1 atom at the center. 1 Unit cell contains: x 1/8 = 2 atoms/unit cell. 4R = Each corner atom is shared among 8 unit cells Diagonals of the cube 9

Fig 1.32

Face Centered Cubic (FCC) 1/2 atom at the center of each face. 1/2 atom at the center of each face. 1/8 atom at each corner. 1/8 atom at each corner. 1 Unit cell contains: 1 Unit cell contains: ½ x x ⅛= 4 atoms/unit cell. ½ x x ⅛= 4 atoms/unit cell. Diagonals of the face (square) Face-centered atoms only belong to two unit cells 11

Fig 1.39

Diamond unit cell 1/2 atom at the center of each face. 1/2 atom at the center of each face. 1/8 atom at each corner. 1/8 atom at each corner. 1 atom at the quarter of each diagonal. 1 atom at the quarter of each diagonal. (there are 4 diagonals for the cube) (there are 4 diagonals for the cube) 1 Unit cell contains: 1 Unit cell contains: ½ x x ⅛ + 4= 8 atoms/unit cell. ½ x x ⅛ + 4= 8 atoms/unit cell. = 8R = 8R 14

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Silicon A silicon ingot is a single crystal of Si. Within the bulk of the crystal, the atoms are arranged on a well-defined periodical lattice. The crystal structure is that of diamond. |Courtesy of MEMC, Electronic Materials Inc.

Left: A polycrystalline diamond film on the (100) surface of a single crystal silicon wafer. The film thickness is 6 microns and the SEM magnification is Right: A 6-micron-thick CVD diamond film grown on a single crystal silicon wafer. SEM magnification is 8000.

Fig 1.43