QuantumDot Lasers Nanoelectronics term project R 91543013 Outline

Quantum-Dot Lasers Nanoelectronics term project R 91543013 徐維良 指導教授: 劉致為

Outline o o o 半導體雷射與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

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>10^10 cm^-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 d. B) • Ith < 20 m. A for all periods (. λ = 33 nm)

溫度穩定性 • Stable single mode emission • No mode hopping • Single mode operation over 194 K 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)

1. 3 µm Quantum Dot Lasers o o o 替代昂貴的In. P-based material system Growth on Ga. As substrates, --便宜、 大的WAFER面積(6", 8") special dot 優點 --low threshold density --broad gain function --low temperature sensitivity

In. As/Ga. In. As Quantum Dots • In. As embedded in Ga. In. As buffer layers – Room temperature emission at 1. 3 µm – High quantum dot density • Growth rate: r(Ga. As) = 1 µm/h r(In. As) = 140 to 260 nm/h • Growth temperature: T = 510 °C

1. 3 µm Quantum Dots

1. 3 µm Quantum Dots • High dot densities for In. As on Ga. In. As • 35 - 40 me. V line width • 60 me. V level distance • Longer wavelength at higher In content

1. 3 µm Quantum Dot Laser • 6 In. As/Ga. In. As Q-Dot layers with 50 nm Ga. As spacers • 650 nm cavity width • GRINSCH with SSL structure • 1, 6 µm Al 0. 4 Ga 0. 6 As cladding layers

1. 3 µm Quantum Dot 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/cm 2)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 • 3 d. B 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 m. A, Top. > 150°C)

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