Quantum-Dot Lasers
Nanoelectronics term project
R91543013
徐維良
指導教授:劉致為
Outline
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半導體雷射與Quantum dot laser
Quantum dot laser的製造
Quantum dot laser的特色
高能的Quantum dot laser
1.3 µm Quantum Dot Lasers
結論
半導體雷射
LASER:Light Amplification by
Stimulated Emission of
Radiation
必要的元件:
--Gain medium
--Optical feedback
•利用Quantum dot transition 的放射結合來放大.
•Pumping over p-n junction by current injection
•利用水晶面來反射以共振
增益與尺寸
Quantum Dot的好處
Discrete energy level : high density of states
no temperature dependence
Quantum Dot的好處
reduced diffusion
→ no diffusion to surfaces
reduced active volume
→ low absorption, low inversion densities
refractive index decoupled from carrier density
→ no chirp
Quantum dot laser的製造
MBE-Growth
Integration of Quantum dot layer into
the active zone of a semiconductor
laser
Dot density>10^10cm^-2
改良Carrier Confinement
•SSLs as 布拉格反射體
•改良Carrier Confinement
Quantum dot laser的active
region對於thermal losses較
敏感
改良Carrier Confinement
不同區域的short period superlattices 之結合
mini bandgap 的部分重合導致effective barrier height的增加
溫度與Quantum dot laser
Operation temperature > 210 °C
Reduced wavelength shift:
QW: 0.33 nm/K
QDots: 0.17 - 0.19 nm/K
Quantum dot laser 之增益
•About 3 times broader gain spectrum due to dot size
distribution
•Much larger tuning range for wavelength tuning of DFB
lasers
Single mode Emitting Quantum dot
lasers
•使用E-Beam製造
• Wavelength selection by grating
periode (SMSR = 52 dB)
• Ith < 20 mA for all periods
(.λ = 33 nm)
溫度穩定性
•Stable single mode emission
•No mode hopping
•Single mode operation over
194K temperature range
•三倍大的頻寬
•溫度飄移少一倍
Quantum Dot 與Quantum Well
• Reduced threshold current density for L > 2.5 mm (cross over)
• Lower optical confinement for QDots, but inversion condition is
relaxed
Material Gain of Q-Dot and QWLaser
波長對溫度敏感度
Quantum dot laser有較
低的溫度敏感度
△λ/ △ T
= 0.35 nm/K for QWLs
= 0.23 nm/K for QDLs
高能的Quantum dot laser
• 2 mm × 100 µm broad area laser
• Record value of 4 W cw output power
• Wall plug efficiency > 50 % at 1 W
高能的Quantum dot laser
• Emission by fundamental mode
• High temperature stability
• Low wavelength shift (for QWs 50% higher)
高能的Quantum dot laser
•在20°C 與 80°C 的區域中，每增
加一瓦的能量，只有多百分之二十
的電流
•高的characteristic
temperature
T= 110 K up to 110 °C
1.3 µm Quantum Dot Lasers
 替代昂貴的InP-based material system
 Growth on GaAs substrates,
--便宜、 大的WAFER面積(6", 8")
 special dot 優點
--low threshold density
--broad gain function
--low temperature sensitivity
InAs/GaInAs Quantum Dots
•InAs embedded in GaInAs buffer layers
– Room temperature emission at 1.3 µm
– High quantum dot density
• Growth rate: r(GaAs) = 1 µm/h
r(InAs) = 140 to 260 nm/h
• Growth temperature: T = 510 °C
1.3 µm Quantum Dots
1.3 µm Quantum Dots
• High dot densities
for InAs on GaInAs
• 35 - 40 meV line
width
• 60 meV level
distance
• Longer wavelength
at higher In content
1.3 µm Quantum Dot Laser
•6 InAs/GaInAs Q-Dot layers
with 50 nm GaAs spacers
• 650 nm cavity width
• GRINSCH with SSL
structure
• 1,6 µm Al0.4Ga0.6As
cladding layers
1.3 µm Quantum Dot Laser
Laser emission by
fundamental mode
• 800 µm resonator
length possible
without mirror
coating
•
Threshold Current Density
• For 6 Q-Dot layers threshold doubles but 800 µm device length
possible
• For 3 Q-Dot layers low threshold current density (100 - 200
A/cm2)but limitation to about 2.5 mm resonator length
Modal Gain of Quantum dot Layers
• L = shortest resonator
length at which laser
operation is still possible
on the ground state
• About 2 - 3 cm-1 modal
gain per dot layer
• Best results with 6 dot
layers achieved
Tuning Range of QDot-Lasers
• Linear correlation of grating
period and emission avelength
– Tuning range > 35 nm
– Basic device properties are
almost identical over the whole
tuning range
→ A further extension of the
tuning range to longer and
shorter wavelengths should be
possible
高頻特性
• Large modulation bandwidth
for 800 µm long HR/HR
coated device
• 3dB bandwidth thermally
limited
結論
• Quantum dot laser 的好處
– 低很多的 inversion carrier density
(低 threshold current)
– 對溫度較不敏感
– 有大的頻寬
– low chirp
結論
• 已實體化的 Quantum dot laser
– 980 nm single mode emitting laser with
extremely high temperature
stability (Top = 15 °C - 210 °C)
– 980 nm high power lasers (4 W cw output power,
> 50% wall plug eff.)
– 1.3 µm laser with high device performance
(Ith = 4.4 mA, Top. > 150°C)
Reference
http://www.compoundsemiconductor.net/articles/news/6/3/21/1
http://fibers.org/articles/fs/6/12/3/1
http://fibers.org/articles/fs/6/11/3/1
http://www.ee.leeds.ac.uk/nanomsc/presentations/module2presen
tation.htm
http://www.indianpatents.org.in/ach/quant.htm
http://newton.ex.ac.uk/aip/physnews.595.html
http://www.aip.org/enews/physnews/2003/
http://www.elec.gla.ac.uk/groups/nanospec/dotlaser.html
http://www.shef.ac.uk/uni/academic/NQ/phys/research/semic/qdresgroup.html#Laser
Reference
http://optics.org/articles/ole/7/8/2/1
http://feynman.stanford.edu/Html-CQED/sqdl.html
http://www.hinduonnet.com/thehindu/2001/09/13/stories/081300
06.htm
http://www.phy.ncu.edu.tw/so/Chinese/Quantum%20Dots/Search
%20subject1.htm
http://www.sciam.com.tw/read/readshow.asp?FDocNo=121&DocN
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L.A.Coldren and S.W.Corzine, Diode Lasers and Photonic Integrated
Circuits (Wiley, New York 1995).
M.Asada, Y.Miyamoto, and Y.Suematsu, IEEE J.Quantum Electron.
QE-22, 1915(1986).
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