Molecular Beam

Epitaxy 101a

CRYSTAL STRUCTURE Section 1.1

Planes and directions

Family Singular

{hkl} e.g. {100}

(hkl) e.g. (100), (010), (001), (10̅0), (010̅), (001)̅

<hkl> e.g. <100>

[hkl] e.g. [100], [010], [001], [10̅0], [010̅], [001]̅

Face centred cubic (FCC)

As-FCC Ga-FCC

http://www.dawgsdk.org/crystal/en/library/

Interleaved FCC

http://www.dawgsdk.org/crystal/en/library/

Tetramer

http://www.dawgsdk.org/crystal/en/library/

Zinc-blende

http://www.dawgsdk.org/crystal/en/library/zinc-blende#0000

Planes “top down”

The face of a fcc lattice is a {001} plane

[100]

[010]

Each face has 2 atoms per a2

Monolayer (ML) An atomic layer of a plane

• Atoms per cm2

– 2 atoms per a2 is a non-SI unit

– a for GaAs is 5.65338 Å

– a2 is therefore 31.961 Å2 or 0.31961 nm2

– 2 atoms per 0.31961nm2 is 6.258 atoms/nm2

– ...Or 6.258 x 1014 atoms/cm2

– One ML is 6.258 x 1014 Ga and As atoms/cm2

• Atoms per cm3 – 4 + (1/2 x 6) + (1/8 x 8) = 8 atoms per a3

– 4.428 x 1022 atoms/cm3

ML steps

Ga

Ga

As

As

As

a

a/2

[001]

[110]

Offcut and steps

• Ingot – Czochralski process

• Slice • Step density • 0.1°

– ~105 steps – ~150nm wide

Thin films on thick substrates Substrates and templates

GaAs/GaAs(100)

GaAs/Ge/Si