????????? GaAs(110)?????????

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????????? GaAs(110)?????????

• ???,????,????,????,
• Loren PfeifferA,Ken WestA
• ?????,CREST,???
• ?????? ??A

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Previous Experiments

• Novel growth-interrupt annealing technique with a
  cleaved-edge overgrowth (CEO) method in MBE
  growthAtomically flat (110) GaAs quantum well
• 1 M. Yoshita , H. Akiyama, L. N. Pfeiffer, K.
  W. West Jpn. J. Appl. Phys. 40, L252-254 (2001).
  
• Slight variation in Ga supply results in the
  formation of characteristic surface step-edge
  patterns such as 2- or 3-ML high- islands or
  1-ML-deep pits
• 2 M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W.
  West, Appl. Phys. Lett. 81, 49-51 (2002)

600 ? 10 min
5X5 mm
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Characteristic Surface Forms on Atomically Flat
Surface
2- or 3-ML high islands
110
1-ML-deep pits
001
3 J. W. Oh, M. Yoshita , H. Akiyama, L. N.
Pfeiffer, K. W. West, Appl. Phys. Lett. 82,
1709-1711,2003.
Applied Physics Letters Cover !
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Purpose of experiment

• Excitation by Ti-Sa laser (730nm) gt He-Ne laser
  (630nm) in previous ones lower excit. energy
• Carrier diffusion on atomically flat (110) GaAs
  /GaAlAs QW and its dependences on temp.
  (4K-10K-30K-60K) observed by point and uniform
  optical excitation

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Ti-Sa Ext.(730nm) on various sample position with
uniform excitation
PL
Ti-Sa
mm
Atomically Flat
10nm
mm
10nm
6nm
6.8 mm
GaAs
29 AlGaAs
AlGaAs
mm
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Characteristic PL images of Samples in low temp
region
4K 10K 30K 60K
1-ML Deep Pits
mm
5 X 5 mm
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2-3 ML High Islands
4K 10K 30K 60K
1 mm
mm
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Measurement of Diffusion Length at various
lowtemperature with point excitation
PL
Reflection image
FWHM0.95mm
6.8 mm
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Spot PL images at various low temperature
30K
4K
2mm
60K
100K
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Diffusion on Atomically Flat surface
At 30K t4000 ps m4000
By Hilmer et. al. Phys. Rev. B.42. 3220-3223
(1990)
in our data
Longer diffusion length
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Conclusion

• Observation of unique surface forms on
  atomically flat (110) interface in GaAs/GaAlAs QW
  via microscopic PL imaging
• 1-ML-deep pits dark triangular regions
  (higher energy regions carriers flow outside)
• 23 ML-high islands bright PL spots (lower
  energy regions carriers flow inside)
• Carrier diffusion length in low temp. by
  point excitation efficient carrier migration
  over 1 mm scale even at 4K which increases with
  temp
• Increasing PL image contrast with growing
  temp well explained by the measured

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