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Transcript of Controlled Spontaneous Lifetime in Microcavity Confined InGaAlAs/GaAs Quantum Dots L. A. Graham et...
![Page 1: Controlled Spontaneous Lifetime in Microcavity Confined InGaAlAs/GaAs Quantum Dots L. A. Graham et al, Appl. Phys. Lett., 72, 1670 (1998) Itoh Laboratory.](https://reader035.fdocuments.in/reader035/viewer/2022062304/56649f485503460f94c6a703/html5/thumbnails/1.jpg)
Controlled Spontaneous Lifetime in Microcavity Confined InGaAlAs/GaAs Quantum Dots
L. A. Graham et al, Appl. Phys. Lett., 72, 1670 (1998)
Itoh Laboratory
Masataka Yasuda
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Abstract
Control of spontaneous lifetime of microcavity including quantum dots
• Advantage of using quantum dots as light emitter• Relation between luminescence wavelength and lifetime• Factor to decide lifetime• Comparison between measurements and calculated value
About this paper
![Page 3: Controlled Spontaneous Lifetime in Microcavity Confined InGaAlAs/GaAs Quantum Dots L. A. Graham et al, Appl. Phys. Lett., 72, 1670 (1998) Itoh Laboratory.](https://reader035.fdocuments.in/reader035/viewer/2022062304/56649f485503460f94c6a703/html5/thumbnails/3.jpg)
Contents
• Introduction– Cavity QED– Microcavity– Distributed Bragg Reflector
• Purpose
• Experimental
• Results and Discussion
• Summary
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Cavity QED
Example:Spontaneous emission can be reinforced to a specific direction.
Lifetime of reinforced spontaneous emission is shortened.
Cavity QED (Quantum Electrodynamics): 共振器量子電磁力学
Spontaneous emission was an uncontrollable phenomenon.
But it is possible to control it by using the resonator of the size about wavelength.
Introduction
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Application
Semireflectingmirror
Mirror
Flash lamp
Laser medium
Laser medium: レーザー媒質Semireflecting mirror: 半反射鏡
Introduction
Spontaneous emissionStimulated emission
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Microcavity
Microcavity is a resonator of the size about wavelength.
Mirror
Mirror
Light is confined here
http://www.shef.ac.uk/eee/nc35t/new_research/microcavity_pillars_etched_using.html
Introduction
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Distributed Bragg Reflector
DBR (Distributed Bragg Reflector): 分布ブラッグ反射鏡……
Bragg’s law
• Reflectivity is nearly equal to 100%.
• is changed by controlling .
Merits
Incidence lightWavelength:
Refractive index
Introduction
![Page 8: Controlled Spontaneous Lifetime in Microcavity Confined InGaAlAs/GaAs Quantum Dots L. A. Graham et al, Appl. Phys. Lett., 72, 1670 (1998) Itoh Laboratory.](https://reader035.fdocuments.in/reader035/viewer/2022062304/56649f485503460f94c6a703/html5/thumbnails/8.jpg)
Substrate
Structure of microcavity
Spacer
DBR
DBR
The resonator can be miniaturized.
Merit
Ex) AlAs/GaAs DBRs, 30 pairs
Optical path length:
Wavelength of cavity resonance
800 850 900 950 10000
20
40
60
80
100
Ref
lect
ivity
[%]
Wavelength [nm]
Introduction
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Low dimensional structuresD
OS D
OS D
OS
energy energy energy
Quantum well Quantum wire Quantum dot (QD)
stepwisediscrete
Introduction
dephasinghigh low
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Purpose
• To measure the spontaneous lifetimes in t
he microcavity confined InGaAlAs/GaAs Q
Ds structure at various wavelengths.
• To compare the results of lifetime depende
nce with calculated predictions.
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Sample
GaAs substrate
5000Å GaAs buffer layer
15.5 pair AlAs/GaAs DBRs
1300Å GaAs layer
600°C
spacer Molecular beam epitaxy
6 monolayers of In0.5Ga0.35Al0.15As(QD)520°C 100ÅGaAs layer
360Å AlGaAs layer
680Å GaAs layer
3 pair MgF/ZnSe DBRs
600°C 80Ågraded layer
Electron-beam deposition
DBR
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Reflectivity spectrum
Cavity resonance at 956nm without MgF/ZnSe DBRs.
QDs are placed close to the upper interface of the spacer.
antinode of electric field
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Experimental setup
Ti:Sapphire laser
Grating spectrometer
Sample
Cryostat
• Wavelength:735nm• Pulse width :200fs• Repetition rate:76MHz
Single photon counting module
Microscope objective
Temporal resolution:350ps
Silicon avalanche-photodiode
Pulse pickerTemporal separation:130ns
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Photoluminescence decay
Cavity resonance peak is 9514Å with MgF/ZnSe DBRs.
Spontaneous lifetimes between (a) and (b) are differed.
(a)
(b)
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Calculated emission intensity
(a) Spontaneous
emission is not
reinforced.
→Lifetime is increased.
(b) Reinforced at 12
degrees
→Lifetime is decreased.
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Spontaneous emission pattern
(d) without cavity(c) layout
(e) (f) (g)
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Decay rates
Decay rates change rapidly
near cavity wavelength.
Between measured and
calculated lifetime changes
is good agreement.
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Summary
• Cavity resonance of the microcavity is tuned to PL wavelength of InGaAlAs/GaAs quantum dot.
• The spontaneous lifetimes are different on the boundary of the wavelength of cavity resonance.
• It is possible to control lifetimes by optimizing the QD positioning and the cavity layer thickness.