vancouver 081 free carrier induced substrate heating of the epitaxially grown gamnas institute of...
TRANSCRIPT
Vancouver 08 1
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
Vancouver 08 2
GaMnAsGaMnAs
• Problem: limited Mn solubility
growth at T=220°C growth at T=230°C
7%Mn, 50 nm 7%Mn, 50 nm
Vancouver 08 3
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)
Vancouver 08 4
Band-gap spectroscopyBand-gap spectroscopy
spectrometer
substrate heater
GaAs
160°C sufficient!
>~
Vancouver 08 5
GrowthGrowth
• minimum change in Ts measured by Tc
constant heater power
Vancouver 08 6
GrowthGrowth
• minimum change in Ts measured by Tc
• large change in Ts measured by BES !
constant heater power
Vancouver 08 7
Absorption spectrumAbsorption spectrum
substrate
+ GaMnAs
band-gap region
Vancouver 08 8
Absorption spectrumAbsorption spectrum
really change of Ts !
substrate
+ 40°C
+ GaMnAs
band-gap region
Vancouver 08 9
Absorption spectrumAbsorption spectrum
really change of Ts !
substrate
+ 40°C
+ GaMnAs
band-gap region NIR
phononsfree carriers
substrate
+ GaMnAs
Vancouver 08 10
Model I.Model I.
naively:
solution:
But ! • obscured parameters
• inconsistencies with experiment
Vancouver 08 11
Radiation heat exchangeRadiation heat exchange
1 2
Qin-2
Qout-2Qout-1
Vancouver 08 12
Radiation heat exchangeRadiation heat exchange
1 2
Qin-2
Qout-2Qout-1
Vancouver 08 13
Radiation heat exchangeRadiation heat exchange
phononsinterband
• substrate/epilayer absorptance s()
abso
rpta
nce
Vancouver 08 14
Radiation heat exchangeRadiation heat exchange
phononsinterband
free holes
abso
rpta
nce
• substrate/epilayer absorptance s()
Vancouver 08 15
Radiation heat exchangeRadiation heat exchange
phononsinterband
free holesabso
rpta
nce
• substrate/epilayer absorptance s()
Vancouver 08 16
Radiation heat exchangeRadiation heat exchange
phononsinterband
free holes
abso
rpta
nce
• substrate/epilayer absorptance s()
Vancouver 08 17
Radiation heat exchangeRadiation heat exchange
phononsinterband
• radiation sources
free holes
~250°C
abso
rpta
nce,
rad
ianc
e
Vancouver 08 18
Radiation heat exchangeRadiation heat exchange
phononsinterband
~900°C
• radiation sources
free holes
abso
rpta
nce
abso
rpta
nce,
rad
ianc
e
~250°C
Vancouver 08 19
Radiation heat exchangeRadiation heat exchange
phononsinterband
• radiation sources
free holes
backgroundabso
rpta
nce,
rad
ianc
e
~250°C
~900°C
Vancouver 08 20
Radiation heat exchangeRadiation heat exchange
phononsinterband
• substrate radiation
free holes
background
substrate
abso
rpta
nce,
rad
ianc
e
~250°C
~900°C
Vancouver 08 21
Model II.Model II.
better:
heater ( 200°C )
cells ( ~ 900°C )
background ( > 77K, < 200°C )
i : >~
s(, t) :t
f
Vancouver 08 22
ResultsResults
before growth: long after growth:
Vancouver 08 23
ResultsResults
before growth: long after growth:
time evolution: Th = 320°C
Tc = 950°C
Tb = 40°C
Vancouver 08 24
Implications for Implications for T T reductionreduction• TBES-locked substrate heater power
(problem: heat capacity of heater)
Vancouver 08 25
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
Vancouver 08 26
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
Vancouver 08 27
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
Vancouver 08 28
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
Vancouver 08 29
Bonus: record Curie temperatureBonus: record Curie temperature
185K
also: Nottingham group
Thank you !Thank you !