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Free carrier induced substrate heating of the epitaxially grown GaMnAs

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.

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Free carrier induced substrate heating of the epitaxially grown GaMnAs

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  1. Free carrier induced substrate heating of the epitaxially grown GaMnAs Institute of Physics AS CR, Prague Vit Novak, Kamil Olejnik, Miroslav Cukr

  2. GaMnAs • Problem: limited Mn solubility 7%Mn, 50 nm 7%Mn, 50 nm growth at T=230°C growth at T=220°C

  3. Measuring 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)

  4. > ~ Band-gap spectroscopy GaAs substrate heater spectrometer 160°C sufficient!

  5. Growth constant heater power • minimum change in Ts measured by Tc

  6. Growth constant heater power • minimum change in Ts measured by Tc • large change in Ts measured by BES !

  7. Absorption spectrum band-gap region substrate + GaMnAs

  8. Absorption spectrum band-gap region substrate + GaMnAs + 40°C really change of Ts !

  9. Absorption spectrum band-gap region NIR substrate substrate + GaMnAs + GaMnAs + 40°C phonons free carriers really change of Ts !

  10. Model I. naively: solution: But ! • obscured parameters • inconsistencies with experiment

  11. Radiation heat exchange 1 2 Qout-2 Qout-1 Qin-2

  12. Radiation heat exchange 1 2 Qout-2 Qout-1 Qin-2

  13. Radiation heat exchange • substrate/epilayer absorptance as(l) absorptance phonons interband

  14. Radiation heat exchange • substrate/epilayer absorptance as(l) absorptance free holes phonons interband

  15. Radiation heat exchange • substrate/epilayer absorptance as(l) absorptance free holes phonons interband

  16. Radiation heat exchange • substrate/epilayer absorptance as(l) absorptance free holes phonons interband

  17. Radiation heat exchange • radiation sources ~250°C absorptance, radiance free holes phonons interband

  18. Radiation heat exchange • radiation sources ~900°C ~250°C absorptance absorptance, radiance free holes phonons interband

  19. Radiation heat exchange • radiation sources ~900°C ~250°C absorptance, radiance free holes background phonons interband

  20. Radiation heat exchange • substrate radiation ~900°C substrate ~250°C absorptance, radiance free holes background phonons interband

  21. > ~ Model II. better: i: heater( 200°C ) cells( ~ 900°C ) background ( > 77K, < 200°C ) af as(l, t) : t

  22. Results before growth: long after growth:

  23. Results before growth: long after growth: time evolution: Th = 320°C Tc= 950°C Tb= 40°C

  24. Implications for DT reduction • TBES-locked substrate heater power • (problem: heat capacity of heater)

  25. Implications for DT reduction • TBES-locked substrate heater power • (problem: heat capacity of heater) • sample holder (or sample!) with initially strong IR absorption

  26. Implications for DT reduction • TBES-locked substrate heater power • (problem: heat capacity of heater) • sample holder (or sample!) with initially strong IR absorption

  27. Implications for DT reduction • TBES-locked substrate heater power • (problem: heat capacity of heater) • sample holder (or sample!) with initially strong IR absorption

  28. Implications for DT reduction • TBES-locked substrate heater power • (problem: heat capacity of heater) • sample holder (or sample!) with initially strong IR absorption w/ sublayer on Mo-block

  29. 185K Bonus: record Curie temperature also: Nottingham group Thank you !

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