Quantum-Dot Lasers Nanoelectronics term project R 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: 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

High dot densities for InAs on GaInAs 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 ( 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 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 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 °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 tation.htm Q/phys/research/semic/qdresgroup.html#Laser

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