free carrier induced substrate heating of the epitaxially grown gamnas
DESCRIPTION
Free carrier induced substrate heating of the epitaxially grown GaMnAs. Institute of Physics AS CR, Prague. Vit Novak, Kamil Olejnik, Miroslav Cukr. GaMnAs. Problem: limited Mn solubility. 7%Mn, 50 nm. 7%Mn, 50 nm. growth at T=230 ° C. growth at T=220 ° C. Measuring the (low) temperature. - PowerPoint PPT PresentationTRANSCRIPT
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Free carrier induced substrate Free carrier induced substrate heating of the epitaxially grown heating of the epitaxially grown GaMnAsGaMnAs
Institute of Physics AS CR, Prague
Vit Novak, Kamil Olejnik, Miroslav Cukr
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GaMnAsGaMnAs
• Problem: limited Mn solubility
growth at T=220°C growth at T=230°C
7%Mn, 50 nm 7%Mn, 50 nm
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Measuring the (low) temperatureMeasuring the (low) temperature
• thermocouple x poor coupling
• optical pyrometry x weak radiation
x substrate transparent
• Band-gap spectroscopy
Shanabrook et al. (1992), Johnson et al. (1993),
Thompson et al. (1997)
commercially by kSA (BandiT)
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Band-gap spectroscopyBand-gap spectroscopy
spectrometer
substrate heater
GaAs
160°C sufficient!
>~
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GrowthGrowth
• minimum change in Ts measured by Tc
constant heater power
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GrowthGrowth
• minimum change in Ts measured by Tc
• large change in Ts measured by BES !
constant heater power
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Absorption spectrumAbsorption spectrum
substrate
+ GaMnAs
band-gap region
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Absorption spectrumAbsorption spectrum
really change of Ts !
substrate
+ 40°C
+ GaMnAs
band-gap region
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Absorption spectrumAbsorption spectrum
really change of Ts !
substrate
+ 40°C
+ GaMnAs
band-gap region NIR
phononsfree carriers
substrate
+ GaMnAs
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Model I.Model I.
naively:
solution:
But ! • obscured parameters
• inconsistencies with experiment
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Radiation heat exchangeRadiation heat exchange
1 2
Qin-2
Qout-2Qout-1
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Radiation heat exchangeRadiation heat exchange
1 2
Qin-2
Qout-2Qout-1
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Radiation heat exchangeRadiation heat exchange
phononsinterband
• substrate/epilayer absorptance s()
abso
rpta
nce
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Radiation heat exchangeRadiation heat exchange
phononsinterband
free holes
abso
rpta
nce
• substrate/epilayer absorptance s()
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Radiation heat exchangeRadiation heat exchange
phononsinterband
free holesabso
rpta
nce
• substrate/epilayer absorptance s()
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Radiation heat exchangeRadiation heat exchange
phononsinterband
free holes
abso
rpta
nce
• substrate/epilayer absorptance s()
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Radiation heat exchangeRadiation heat exchange
phononsinterband
• radiation sources
free holes
~250°C
abso
rpta
nce,
rad
ianc
e
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Radiation heat exchangeRadiation heat exchange
phononsinterband
~900°C
• radiation sources
free holes
abso
rpta
nce
abso
rpta
nce,
rad
ianc
e
~250°C
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Radiation heat exchangeRadiation heat exchange
phononsinterband
• radiation sources
free holes
backgroundabso
rpta
nce,
rad
ianc
e
~250°C
~900°C
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Radiation heat exchangeRadiation heat exchange
phononsinterband
• substrate radiation
free holes
background
substrate
abso
rpta
nce,
rad
ianc
e
~250°C
~900°C
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Model II.Model II.
better:
heater ( 200°C )
cells ( ~ 900°C )
background ( > 77K, < 200°C )
i : >~
s(, t) :t
f
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ResultsResults
before growth: long after growth:
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ResultsResults
before growth: long after growth:
time evolution: Th = 320°C
Tc = 950°C
Tb = 40°C
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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
• sample holder (or sample!) with initially strong IR absorption
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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
• sample holder (or sample!) with initially strong IR absorption
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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
• sample holder (or sample!) with initially strong IR absorption
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Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
on Mo-block
w/ sublayer
• sample holder (or sample!) with initially strong IR absorption
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Bonus: record Curie temperatureBonus: record Curie temperature
185K
also: Nottingham group
Thank you !Thank you !