Quantum-Dot Lasers

Nanoelectronics term project R91543013 徐維良 指導教授 : 劉致為

Outline

      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 µ m 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 QW Laser

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 µ m 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

µ

m 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 µ m – High quantum dot density Growth rate: r(GaAs) = 1 µ m/h r(InAs) = 140 to 260 nm/h Growth temperature: T = 510 ° C

1.3

µ

m Quantum Dots

1.3

µ

m 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

µ

m Quantum Dot Laser

• • •6 InAs/GaInAs Q-Dot layers with 50 nm GaAs spacers 650 nm cavity width GRINSCH with SSL structure • 1,6 µ m Al0.4Ga0.6As

cladding layers

1.3

µ

m Quantum Dot Laser

• Laser emission by fundamental mode • 800 µ m resonator length possible without mirror coating

Threshold Current Density

• For 6 Q-Dot layers threshold doubles but 800 µ m 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 µ m long HR/HR coated device • 3dB bandwidth thermally limited

結論

• Quantum dot laser 的好處 – – – – 低很多的 ( 低 inversion carrier density 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 µ m 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/N Q/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 o=191 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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