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Low-threshold T-shaped Quantum Wire Lasers by Arm-
arm Current Injection
ISSP, Univ. of Tokyo, and CREST, JST, Bell Lab, Lucent TechnologiesA
S.M.Liu, M. Yoshita, M. OKano, T. Ihara, H. Itoh, H. Akiyama, L. PfeifferA, K.WestA, and K.
BaldwinA
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Content
Introduction Characteristics of our low threshold lasers,
including
arm-arm current injection scheme;
emission spectra and images;
I-L and I-V curves. Summary
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Introduction
Why low threshold?
LOW THRESHOLD lasers are attractive for optical communicatio
n systems because of the tight packing density, low power con
sumption and high modulation bandwidth.
How to get low-threshold?
Ideal QUANTUM WIRE lasers are predicted to show ultralow thre
shold current of several A due to small volume of active region a
nd large density of states at the subband edges.
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Theoretical threshold current for 3,2,and 1D system(A. Yariv APL 53, 1033 (1988))
In which, the transparency carrier density
Assuming infinite potential well depth; Involving only the first quantized states.
Quantum well lasers: 100 A; Quantum wire lasers: 2-3 A.
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Previous experimental results I (V-groove)
V-groove QWRs9 nm X 80-100 nmIth=50 mA
1989: Kapon et al, Phys. Rev. Lett. 63, 430
V-groove quantum wire lasers grown on patterned substrates
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3-period V-groove QWRs with Si3N4 mask10 nm X 35 nmIth=0.19 mA
Previous experimental results II (V-groove)
1994: Tiwari et al, Appl. Phys. Lett. 64, 3536
Lowest threshold current of V-groove quantum wire lasers
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Previous experimental results III (T-shaped)
1994: Wegscheider et al, Appl. Phys. Lett. 65, 2510
15-period 7 nm X 7nm T-wiresIth=0.4-0.7 mA @ 4K
T-shaped quantum wires provide smaller size and higher array density
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Previous experimental results IV (DFB)
2005: Yagi et al, Appl. Phys. Lett. 87, 223120
InGaAsP/InP QWR DFB laser9 nm x 24 nm EB lithography, dry and wet etching, MOCVD growthcw 1.5 m-wavelength lasing Ith= 2.7 mA @ r.t.
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Current injection schemes of T-wire lasers
stem well
arm well
arm-stem injection arm-arm injection
24aXL-12 Okano et al.
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MBE growth of arm-arm injection laser
C-doped MQWs
Si-doped MQWs
lower cladding
upper cladding
stem MQWs
Si-doped buffer layers
p-contact
sid
e cl
addi
ng
arm well
n+ GaAs substrate
n-contact
Current confinement in the single arm well
Cavity length: 500 mHR/HR coating by Au(300nm/50nm)
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EL and lasing spectra @ 30K
• No EL or lasing from stem well indicating current confinement in the arm well;
• Single mode lasing above threshold;
• Similar spectra from 30-70K.
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EL images @ 30K
Stem MQWsCladding layer
C-doped MQWs
Cladding
layer
Cladding layer
Si-doped layers
GaAs n+ substrate
2m
0.01mA
42 196
Tight optical confinementabove Ith
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Power out & voltage vs current
I-L
V-I
20-period T-wire laser6nm X14nm per wirec.w.HR/HRL=500 m
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Temperature dependence
Threshold current: 0.27-0.76 mADifferential quantum efficiency: 12%-8.2%
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Summary
Arm-arm injection scheme makes current confinement in the single arm well;
A very low threshold current of 0.27 mA has been achieved @ 30K from a 500 m device under cw operation;
Lasing mechanism will be presented by
Dr. Yoshita 24aXL-11