Effect of a pn junction on the diffusion of excitons

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Effect of a p-n junction on the diffusion of
excitons
Research Practicum 2004 at the OptoElectronic
Materials Group
Prof. dr. hab. T. Gregorkiewicz Drs. N.Q.
Vinh Dr. H. Vrielinck
Our international team
M. van de Meent S. Kowalczyk
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Outline

• Introduction
• Samples
• Excitons the effects of a p-n junction
• Experimental setup
• Experimental results
• Conclusions

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- Memory - Processors
Long time ago Stone Age 17th century Golden
Age Nowadays Silicon Age
Fundamental limit comes in sight quite fast ?
fundamentally different technology will be needed
soon ...
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Erbium-doped silicon has great photonic potential
Emission at 1540 nm, minimal losses in optical
fibers
SiEr can be integrated in silicon technology
(electronics and optoelectronics)
Intense room-temperature photoluminescence for
crystalline silicon
Not yet therefore we try to understand this
process at low temperatures first
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The samples

• Ion-implanted
• SMBE monolayer
• SMBE multilayers

Doping by ion implantation
Mini AK47-erbium gun
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Erbium-related level
donor
Ionization energy in the 0.1 - 0.25 eV range.
luminescence
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Emission at 1540 nm from inner 4f-shell
Erbium concentration is 1018 cm -3
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bound electron-hole pair
Energy transfer by exciton
emission _at_ 1.54 µm
Energy transport by exciton
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Experiments tell us something different than
theory
Delay-time 1 ms (experiment) Diffusion-time 1
µs
t s2/4D
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possible explantion Exitons have to destruct
the depletion region associated with a p-n
junction before they can pass and this takes some
time.
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What is a p-n junction?
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What is a depletion region?
free of mobile charge carriers
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an anology depletion region / river
SiEr
Si
Laser
e
h
e
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an anology depletion region / river
SiEr
Si
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an anology depletion region / river
SiEr
Si
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an anology depletion region / river
SiEr
Si
Photoluminescence
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Experimental setup
Argon laser (514 nm)
Mirror
Chopper (freq 38 Hz)
Spectrometer
Polarizer
Detector
Si/SiEr sample
Lens
Mirror
1 meter
Mirror
Very cold vacuum inside
From frontside
(10 K 10-6 mbar)
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Experimental setup
Argon laser (514 nm)
Mirror
Chopper (freq 38 Hz)
Spectrometer
Polarizer
Detector
Si/SiEr sample
Lens
Mirror
1 meter
Mirror
Very cold vacuum inside
From backside
(10 K 10-6 mbar)
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Emission spectra of ion-implanted sample
1540 nm
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PL rise times
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Delay time
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Rise time
s 1.04 10-13 cm2 tEr 4 ms
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Decay
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Bias
Do it this week
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SMBE monolayer
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SMBE multilayer
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Conclusions

• Excitons play an essential role in Erbium
  excitation mechanism
• Observation delay time depends on power
• Rise time depends on power gt excitation cross
  section
• SMBE samples no observable Er-PL from backside