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Molecular Beam
Epitaxy
GROWTH DYNAMICS Section 3
Growth rates ML/s or Å/s or µm/h?
GaAs(100) (a=5.65338 Å)
• 1ML = 6.258 x 1014 atoms/cm2
• ~ 0.283 nm/s or ~ 2.83 Å/s
• ~ 1.018 µm/h
InAs(100) (a = 6.05840 Å)
• 1ML = 5.449 x 1014 atoms/cm2
• ~ 0.303 nm/s or ~ 3.03 Å/s
• ~ 1.091 µm/h
Ga
Ga
As
As
As
a
a/2
Growth rates ML/s or Å/s or µm/h?
GaAs(100) (a=5.65338 Å)
• 1ML = 6.258 x 1014 atoms/cm2/s
• ~ 0.283 nm/s or ~ 2.83 Å/s
• ~ 1.018 µm/h
InAs(100) (a = 6.05840 Å)
• 6.258 x 1014 atoms/cm2/s is...
– ~ 1.148 ML/s
– ~ 0.348 nm/s or 3.48 Å/s
– ~ 1.252 µm/h
What is the only thing an MBE grower ultimately has control over?
Temperature Magnitude of flux
III:V flux ratio
Growth
• Homoeptiaxy – Elemental Semiconductors (e.g. Si)
• Diffusion length
– Binaries (e.g. GaAs) • Group V only “stick” if there is a group III present • Flux ratios: 1:1, 1.6:1, >2:1 • Diffusion length
• Heteroeptiaxy – Group III (e.g. InGaAs)
• Unity sticking coefficients • Growth temperatures
– Group V (e.g. GaAsP) • Competition in ternaries
• Point defects – Background doping – Anti-sites – Vacancies – Background species
Elemental growth Effect of Temperature
Growth
• Homoeptiaxy – Elemental Semiconductors (e.g. Si)
• Diffusion length
– Binaries (e.g. GaAs) • Group V only “stick” if there is a group III present • Flux ratios: 1:1, 1.6:1, >2:1 • Diffusion length
• Heteroeptiaxy – Group III (e.g. InGaAs)
• Unity sticking coefficients • Growth temperatures
– Group V (e.g. GaAsP) • Competition in ternaries
• Point defects – Background doping – Anti-sites – Vacancies – Background species
Binary Growth Effect of BEPR
Growth
• Homoeptiaxy – Elemental Semiconductors (e.g. Si)
• Diffusion length
– Binaries (e.g. GaAs) • Group V only “stick” if there is a group III present • Flux ratios: 1:1, 1.6:1, >2:1 • Diffusion length
• Heteroeptiaxy – Group III (e.g. InGaAs)
• Unity sticking coefficients • Growth temperatures
– Group V (e.g. GaAsP) • Competition in ternaries
• Point defects – Background doping – Anti-sites – Vacancies – Background species
Group III Ternary Growth Effect of non-unity sticking coefficients
Group III Ternary Growth Segregation
Group III Ternary Growth Dislocations
Growth
• Homoeptiaxy – Elemental Semiconductors (e.g. Si)
• Diffusion length
– Binaries (e.g. GaAs) • Group V only “stick” if there is a group III present • Flux ratios: 1:1, 1.6:1, >2:1 • Diffusion length
• Heteroeptiaxy – Group III (e.g. InGaAs)
• Unity sticking coefficients • Growth temperatures
– Group V (e.g. GaAsP) • Competition in ternaries
• Point defects – Background doping – Anti-sites – Vacancies – Background species
Group V ternary Growth Effect of site competition
Growth
• Homoeptiaxy – Elemental Semiconductors (e.g. Si)
• Diffusion length
– Binaries (e.g. GaAs) • Group V only “stick” if there is a group III present • Flux ratios: 1:1, 1.6:1, >2:1 • Diffusion length
• Heteroeptiaxy – Group III (e.g. InGaAs)
• Unity sticking coefficients • Growth temperatures
– Group V (e.g. GaAsP) • Competition in ternaries
• Point defects – Background doping – Anti-sites – Vacancies – Background species
Point defects Effect of background doping and sub-optimal conditions
MBE Optimisation
• Optimisation: Tgrow and III:V flux ratio
– High Tgrow limit
– Low Tgrow limit
– Low ratio limit
– High ratio limit
– Systematic optimisation of parameters
• Define all parameters
• Step through and feedback
Thought exercise.... GaAs/GaAs(100)
Ga rich Thermal Energy Flux
ratio
Growth temperature
Ga rich
As anti-sites
Variable Complications Outputs
Ga flux AlGaAs cladding PL intensity
As flux Background doping
As species
Growth temperature