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

Shu-man Liu, Masahiro Yoshita, Makoto Okano, 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

CLEO/QELS 2007 in Baltimore (May 7, 2007 CMD5)

Low threshold current in QWR lasers

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= 1 mm, by Tiwari et al. Appl. Phys. Lett. 64, 3536(1994)

1994: Ith=0.4mA, CL/CL, cw, 4.2 K, GaAs/AlGaAs T-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= 330m,

by Yagi et al. Appl. Phys. Lett. 87, 223120(2005)

Theoretical prediction1988: Ith ~ 0.6 A for a single wire laser with R ~ 1 and L = 100 m, by Yariv.

Appl. Phys. Lett. 53, 1033(1988)

Objective: Ultralow threshold current in T-shaped quantum-wire lasers

T-wire by cleaved-edge overgrowth with MBE

High controllability

High crystal quality

Flexibility in doping and current injection

T-shaped Quantum Wire (T-wire) Laser

Parallel injection scheme Confining current in the

single arm well to reduce threshold current

Easy fabrication and processing

Micro-Photoluminescence spectra

Narrow PL peak (FWHM ~ 1 meV) of T-wire indicates high interface quality of wires. Confinement energy ~ 16 meV

Ex: 1.67 eV0.8-m laser spot

Electroluminescence spectra300g/mm Grating

No EL emission from stem wells indicates current confinement in the single arm well as expected.

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)

1200g/mm Grating

30 KGround state lasingSingle mode lasing

Threshold current Ith & differential quantum efficiency d

Output power vs. Current

d vs. T

Ith vs. T

Ith= 0.27mA (20 wires)

According to Yariv’s prediction, Ith = 10 A for L = 500m, T = 30 K, and = 0.4 ns.

APL, 53,1033(1988)

Ith = 14 A (single wire)

Low threshold currentLow threshold current

d = 12 %

High quantum efficiencyHigh quantum efficiency

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

LAATTTT

iid

22121

21

EL imaging measurements

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.

CL/CL

Summary

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)

Laser performances of T-wire laser with a new injection scheme

Single mode lasing from ground states at 30-70 K

Low threshold current (14 A per wire) and high external differential quantum efficiency (12 %) at 30 K.