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Low-threshold Current-Injection Single-Mode Lasing in T-shaped Quantum Wire s

CLEO/QELS 2007 in Baltimore (May 7, 2007 CMD5). Low-threshold Current-Injection Single-Mode Lasing in T-shaped Quantum Wire s. Shu-man Liu , Masahiro Yoshita , Makoto Okano , Toshiyuki Ihara , Hirotake Itoh, Hidefumi Akiyama Institute for Solid State Physics, Univ. of Tokyo and CREST, JST.

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Low-threshold Current-Injection Single-Mode Lasing in T-shaped Quantum Wire s

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  1. CLEO/QELS 2007 in Baltimore (May 7, 2007 CMD5) Low-threshold Current-Injection Single-Mode Lasing in T-shaped Quantum Wires Shu-manLiu, MasahiroYoshita, MakotoOkano, Toshiyuki Ihara, Hirotake Itoh, Hidefumi Akiyama Institute for Solid State Physics, Univ. of Tokyo and CREST, JST Loren N. Pfeiffer, Ken W. West and Kirk W. Baldwin Bell Laboratories, Alcatel-Lucent

  2. Low threshold current in QWR lasers Theoretical prediction 1988: Ith ~ 0.6 A for a single wire laser with R ~ 1 and L = 100 m, by Yariv. Appl. Phys. Lett. 53, 1033(1988) Experimental results 1991:Ith=0.6mA, HR/HR, pulsed, GaAs/AlGaAs V-groove triple wires, L= 135m, by Simhony et al. Appl. Phys. Lett. 59, 2225(1991) 1994:Ith=0.19mA, CL/CL,cw, InGaAs/AlGaAs V-groove triple wires, L= 1mm, by Tiwari et al. Appl. Phys. Lett. 64, 3536(1994) 1994: Ith=0.4mA, CL/CL, cw, 4.2 K, GaAs/AlGaAsT-shaped 15 wires, L = 400 m, by Wegscheider et al. Appl. Phys. Lett. 65, 2510(1994) 2005:Ith=2.7mA, CL/CL, cw, GaInAsP/InP DFB lasers by EB lithography, CH4/H2 reactive ion etching and OMVPE regrowth, L= 330m, by Yagi et al. Appl. Phys. Lett. 87, 223120(2005) Objective:Ultralow threshold current in T-shaped quantum-wire lasers

  3. Parallel injection scheme • Confining current in the single arm well to reduce threshold current • Easy fabrication and processing T-shaped Quantum Wire (T-wire) Laser • T-wire by cleaved-edge overgrowth with MBE • High controllability • High crystal quality • Flexibility in doping and current injection

  4. Micro-Photoluminescence spectra Ex: 1.67 eV 0.8-m laser spot Narrow PL peak (FWHM ~ 1 meV) of T-wire indicates high interface quality of wires. Confinement energy ~ 16 meV

  5. Electroluminescence spectra 300g/mm Grating No EL emission from stem wells indicates current confinement in the single arm well as expected. 30 K Ground state lasing Single mode lasing 1200g/mm Grating • Laser bar • Cavity length of 500 m • cw operation • HR coated facets Front: SiO2(70 nm)/Au(50 nm) Rear: SiO2(70 nm)/Au(300nm)

  6. Threshold current Ith & differential quantum efficiency d High quantum efficiency Low threshold current d= 12 % Ith= 0.27mA(20 wires) + T T h = h 1 2 Ith = 14 A(single wire) d i + + + + a T T A A 2 L 1 2 1 2 i Front facet: SiO2 (70nm)/Au (50 nm) R1=96.8%, T1 = 1%, A1 = 2.2 %; Rear facet: SiO2 (70nm)/Au (300 nm) R2=98.1%, T2 = 0%, A2 = 1.9 %; Assuming i = 1, i = 0.32 cm-1 According to Yariv’s prediction, Ith = 10 A for L = 500m, T = 30 K, and  = 0.4 ns. APL, 53,1033(1988) d vs. T Ith vs. T Output power vs. Current

  7. EL imaging measurements CL/CL • Common feature • No emission from stem well due to current confinement in the arm well as expected from this new injection scheme. • Difference • 30K: Emission is tightly confined in T-wire center at currents above 0.3 mA. • 5K: Strong emission from p-doped layer indicates holes are frozen at 5 K.

  8. Summary • Laser performances of T-wire laser with a new injection scheme • Single mode lasing from ground statesat 30-70 K • Low threshold current (14 A per wire) and high external differential quantum efficiency (12 %) at 30 K. • Two factors contribute to the low-threshold current and high efficiency: • high optical quality of T-wires (narrow PL linewidth and low internal loss) • efficient current injection scheme (no EL emission from stem wells)

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