Basic Crystallography 24 January 2014
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Basic Crystallography 24 January 2014 Three general types of solids 1. Amorphous ― with order only within a few atomic and molecular dimensions (Fig. (a)) 2. Polycrystalline ― with multiple sing-crystal regions (called grains) separated by grain boundary (Fig.(b)) 3. Single crystal ― with geometric periodicity throughout the entire material (Fig. (c)) (a) (b) (c) 1
description
Basic Crystallography 24 January 2014. Three general types of solids Amorphous ― with order only within a few atomic and molecular dimensions (Fig. (a)) Polycrystalline ― with multiple sing-crystal regions (called grains) separated by grain boundary (Fig.(b)) - PowerPoint PPT Presentation
Transcript of Basic Crystallography 24 January 2014
Basic Crystallography
24 January 2014
Three general types of solids 1. Amorphous ― with order only within a few atomic and molecular
dimensions (Fig. (a))2. Polycrystalline ― with multiple sing-crystal regions (called grains)
separated by grain boundary (Fig.(b))3. Single crystal ― with geometric periodicity throughout the entire material
(Fig. (c))
(a) (b) (c)1
Geometric Description of Single-Crystal — Space Lattices
lattice: the periodic arrangement of atoms in the crystal
Lattice:
unit cell: a small volume that can be used to repeat and form the entire crystal. Unit cells are not necessary unique.
Unit cell:
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Space lattices
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A general 3D unit cell is defined by three vectors cba
, ,Every equivalent lattice point in the 3D crystal can be found by
csbqapr
a
b
c
General casea
b
c
Special case
Basic Crystal Structures
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Three common types:
a) Simple cubicb) Body-centered cubic (bcc) c) Face-centered cubic (fcc)
(a) (c)(b)
cba
and
constant lattice cba
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Why Crystal Planes Important?
• real crystals are eventually terminate at a surface
• Semiconductor devices are fabricated at or near a surface
• many of a single crystal's structural and electronic properties are highly anisotropic
1. Find the intercept on the x, y, and z
2. Reduce to an integer. i.e. lowest common denominator
3. Take the reciprocal and reduce to the smallest set of integers (h, k, l) These are called the Miller Indices
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cba ,,
cba ,,
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(100) Plane with normal direction [100]
(110) Plane with normal direction [110]
(111) Plane with normal direction [111]
Examples of Lattice Planes in Cubic Lattices
(100) Plane with normal direction [100]
(110) Plane with normal direction [110]
(111) Plane with normal direction [111]
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Set of Planes
(001)
(010)
Due to the high degree of symmetry in simple cubic, bcc and fcc, the axis can be rotated or parallel shift in each of three dimensions, and a set of plane can be entirely equivalent.
{100} set of planes: (100), (010), (001)
Similarly,
{110} set of planes: (110), (101), (011)
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Set of Planes
(001)
(010)
Due to the high degree of symmetry in simple cubic, bcc and fcc, the axis can be rotated or parallel shift in each of three dimensions, and a set of plane can be entirely equivalent.
{100} set of planes: (100), (010), (001)
Similarly,
{110} set of planes: (110), (101), (011)
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The Diamond Structure
• Materials possess diamond structure: Si, Ge
• 8 atoms per unit cell
• Any atom within the diamond structure will have 4 nearest neighboring atoms
Refer To Crystal WEB Link 12
Volume Density of Atoms
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• Volume density
Number of atoms per unit volume
= Total number of atoms / volume occupied by these atoms
= number of atoms per unit cell/volume of the unit cell
Unit: m-3 or (cm)-3
• Example For Silicon
a= 5.43 Å = 5.43 x 10-8
cm
Volume density =
3223
atoms/cm10x58
a
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Procedure of Silicon Wafer Production
Raw material ― Polysilicon nuggets purified from sand
Crystal pulling
Si crystal ingot
Slicing into Si wafers using a diamond sawFinal wafer product after polishing,
cleaning and inspection
A silicon wafer fabricated with microelectronic circuits
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Identification of Wafer Surface Crystallization
Flats can be used to denote doping and surface crystallization
