Ch 1: Crystal structure of solids

what is a lattice

a set of points in space that defines where atoms will sit (vector)

what is a unit cell

volume repeated to fill up all space

what is a lattice constant

a, periodicity of the lattice

which groups are semiconductor materials

group 4 or group 3 + 5

what are the 3 types of atomic arrangement

1. crystalline: infinite repetition (long range order)

2. polycrystalline: crystal domains (short range order)

3. amorphous: no crystal structure

what are the 3 space lattices

1. simple cubic (SC)

2. body-centered cubic (BCC)

3. face-centered cubic (FCC)

   1. diamond lattice

   2. zinc blende

coordination number of SC

6

coordination number of BCC

8

coordination number of FCC

12

coordination number of diamond lattice

4

coordination number of zinc blende

4

what are miller indices

system of labelling planes and directions for crystals, controls electronic properties

syntax for miller indices: plane, families of planes, direction, families of direction

plane: (hkl)

families of planes: {hkl}

direction: [hkl]

families of direction: <hkl>

how to calculate miller indices?

1. set up axes along unit cell cube edges

2. identify axes intercepts in terms of lattice constant a

3. take recip

4. multiply by lcm and a

5. enclose in round brackets

*no intercepts, intercept at infinity, recip is 0

*negative, overbar

what are the planes for this family {100}

(100), (010), (001), (1 over barr 00), (0 1 overbar 0), (00 1 overbar)

what is packing density

fraction of space spheres occupy in the 3d unit cell or miller plane

what is the atomic packing factor + equation?

fraction of the conventional cubic cell occupied by atoms

APF = n * 4/3pir³/a³

what is the planar packing fraction + equation?

fraction of a miller plane covered by atoms

planar PF = natoms x pir²/A2dcell

what cubric structure does silicon take?

diamond cubic

how many atoms are in silicon

4 + 1/8 × 8 + ½ * 6 = 8

how to calculate cell volume?

V = a³

how to calculate density

n = N/V

what are wafer flats? + the 2 flats

indicates the crystallographic orientation and doping (n,p) type of the wafer

primary flat: longer flat edge

secondary flat: shorter flat edge

what kind of flats does an n type wafer have?

45 degree

180 degree

what kind of flats does a p type wafer have?

only a primary flat

90 degree

what are lattice vibrations

thermal (non zero temp) energy that causes the positions of the nuclei to fluctuate

what are the 2 types of imperfections

point, line

what are the 2 types of point defects

1. vacancy: atom missing from lattice site

2. interstitial: atom located between lattice sites

what is the 1 type of line defect called

line dislocation: extra half plane of atoms ends inside the crystal (edge dislocation)

what are the 2 types of impurities + definitions

• impurity atoms: atoms that are not elements that form the crystal

• doping: controllably adding an impurity (dopant) to change the electrical conductivity of the semiconductor

what are the 2 types of impurity atoms

substitutional: impurity atoms sit on a host lattice site

interstitial: impurity atom site between lattice sites

how does doping work

1. thermal diffusion in a furnace

2. ion implantation: beam of dopant ions

3. anneal at high temperature to repair implant damage and activate the dopant (anneal = heat material then cool it slowly to shape it)