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2004 Fall MRS meeting in Boston (2004.11.30 B3.1)
T-shaped quantum-wire laser
M. Yoshita, Y. Hayamizu, Y. Takahashi, H. Itoh, T. Ihara,
and H. Akiyama
Institute for Solid State Physics, Univ. of Tokyo and CREST, JST
L. N. Pfeiffer, K. W. West, and Ibo Matthews
Bell Laboratories, Lucent Technologies
1. Formation of high-quality GaAs T-shaped quantum wires
Cleaved-edge overgrowth with MBE, AFM, PL, PLE
2. Single-wire laser
PL scan, Lasing, PL, Absorption/Gain via Cassidy’s method, Transmission
3. Observation of RT 1D exciton absorption in 20-wire laser
4. Optical response of n-doped single-wire FET device
T-shaped Quantum Wire (T-wire)
Cleaved-edge overgrowth with MBE
by L. N. Pfeiffer et al., APL 56, 1679 (1990).
[110]
[001]
GaAs
substrate
(001) MBE Growth
600oC
Cleave
in situ
o
(490 C)
(110) MBE Growth
490oC
Nomarski
Microscope
Images
of
Cleaved-EdgeOvergrowth
Surfaces
Good
Poor
“Hackling”
Bad
High Quality
T-wire ???
490C Growth
Atomically flat
interfaces
(By Yoshita et al. JJAP 2001)
High Quality
T-wire !?
490C Growth 510-600C Anneal
Atomically flat
interfaces
(By Yoshita et al. JJAP 2001)
High Quality
T-wire !!?
490C Growth 510-600C Anneal
Atomically flat
interfaces
(By Yoshita et al. JJAP 2001)
High Quality
T-wire !!!!!
490C Growth 510-600C Anneal
Atomically flat
interfaces
(By Yoshita et al. JJAP 2001)
20-wire laser sample
14nm x 6nm
1st growth
600C
2nd growth
490C (arm well)
600C 10min anneal
490C (cover layers)
Laser bars
500mm uncoated cavity
PL and PLE
spectra
Sharp PL width
Small Stokes shift
1D free exciton
1D continuum states
T-wire
stem
well
arm
well
(Akiyama et al. APL 2003)
E-field
E-field
// to wire
_I to wire
// to arm well
Single quantum wire laser
Probability of
Photon
Cavity length 500 mm
G=5x10-4
Probability
of Electron
Scanning micro-PL spectra
T-wire
stem well
scan
T-wire
stem well
T=5K
Continuous
PL peak
over 20 mm
PL width
< 1.3 meV
500mm
gold-coated
cavity
Lasing in a single quantum wire
Threshold 5mW
(Hayamizu et al, APL 2002)
Excitation power
dependence of PL
M. Yoshita, et al.
n1D = 1.2 x 106 cm-1
(rs = 0.65 aB)
aB ~13nm
Density
Electron-hole Plasma
n1D = 1.2 x 105 cm-1
(rs = 6.6 aB)
Biexciton+Exciton
EB =2.8meV
n1D = 3.6 x 103 cm-1
(rs = 220 aB)
Free Exciton
n1D ~ 102 cm-1
Absorption/gain measurement based on
Hakki-Paoli-Cassidy’s analysis of
Fabry-Perot-laser emission below threshold
A  (1  R) 2 e l
I (E) 
(1  R  e l ) 2  4R  e l sin 2 θ
1  1 p 1 
   ln 

l  R p 1 
I sum /FSR
p
I min
 :Absorption coeff.
R :Reflectivity
n l  E

c
D. T. Cassidy JAP. 56 3096 (1984)
Free Spectral Range
B. W. Hakki and T. L. Paoli JAP. 46 1299 (1974)
Absorption Spectrum by Cassidy method
Single wire laser, uncoated cavity mirrors
Excitation Light
:cw TiS laser at 1.631eV
Spectrometer
with spectral
resolution of
0.15 meV
Cassidy’s
Method
Point
Waveguide
Emission
Polarization
parallel to
Arm well
Measurement of absorption/gain spectrum
Excitation Light
:cw TiS laser at 1.631eV
Spectrometer
with spectral
resolution of
0.15 meV
Cassidy’s
Method
Spontaneous
emission
Stripe shape
Waveguide
Emission
8.3mW
Polarization
parallel to
Arm well
Absorption/gain spectrum (High excitation
power)
Absorption
Electron-Hole
Plasma
Gain
EBE
EFE
8.3mW
Hayamizu et al.
Electron-Hole
Plasma
1. Exciton peak and continuum
onset decay without shift.
2. Gap between exciton and
continuum is gradually filled.
3. Exciton changes to Fermi
edge
Exciton
Hayamizu et al.
Transmission measurement
of a single quantum wire
~mm
~nm
Transmittance for single
Coupling
efficiency
= 20%
Takahashi et al. unpublished
Absorption for single
Takahashi et al. unpublished
Absorption for 20
Y. Takahashi et al.
Absorption
at
300
K
Room-Temperature 1D Exciton Absorption!
Y. Takahashi et al.
1D electron density
14nmx6nm Doped
Single Wire FET
device with tunable
1D electron density
e he
T. Ihara et al.
eh
Quantum-Wire Devices
Summary
1. GaAs T-shaped quantum wires (T-wires) are formed by cleavededge overgrowth with MBE.
2. Growth-interrupt anneals dramatically improve T-wire quality.
3. AFM : No atomic steps over 100mm.
4. PL : Sharp PL width (~1meV) improved by a factor of 10.
5. PLE : Observation of 1D free exciton, & 1D continuum states
6. Single wire lasing : The world thinnest laser (14nm x 6nm),
5mW threshold optical pumping power at 5K.
7. Gain/absorption measurement by Hakki-Paoli-Cassidy’s method.
8. Strong photo-absorption by a single wire
84/cm (98.5% absorption / 500mm) at exciton peak at 5K
9. Room-temperature exciton absorption observed in 20-wire laser.
10. Single-wire FET: carrier-sensitive optical responses.
ここまで。25分のトーク。
(001) and (110) surfaces of GaAs
(001)
[001]
(110)
[110]
[110]
[001]
Growth rate of GaAs
in MBE
Substrate rotation
>>> uniform
Ga limited growth under
As4 overpressure
Interface control by growth-interruption annealing
o
High Quality
T-wire
490 C Growth
o
600 C Anneal
arm
well
6nm
Atomically flat
stem
well
14nm
interfaces
(by M. Yoshita et al.
JJAP 2001)
(By Yoshita et al. APL 2002)
Single wire laser with 500mm gold-coated cavity
Absorption at higher temperatures by Cassidy
Hayamizu et al. unpublished
Absorption coefficients
Experiment for gain
Evolution of continuum
Takahashi et al. unpublished
Lasing & many-body effects in quantum wires
E. Kapon et al. (PRL’89)
W. Wegscheider et al.
(PRL’93)
R. Ambigapathy et al.
(PRL’97)
L. Sirigu et al. (PRB’00)
J. Rubio et al. (SSC’01)
A. Crottini et al. (SSC’02)
T. Guillet et al. (PRB’03)
H. Akiyama et al.
(PRB’03)
Lasing in excited-states of V-wires
Lasing in the ground-state of T-wires, no energy shift,
excitonic lasing
PL without BGR, strong excitonic effect in V-wires
Lasing due to localized excitons in V-wires
Lasing observed with e–h plasma emission in T-wires
PL from exciton molecules (bi-excitons) in V-wires
PL, Mott transition form excitons to a plasma in V-wires
Lasing due to e–h plasma, no exciton lasing in T-wires
Theories
F. Rossi and E. Molinari
(PRL’96)
F. Tassone, C. Piermarocchi, et al.
(PRL’99,SSC’99)
S. Das Sarma and D. W. Wang
(PRL’00,PRB’01)
“1D exciton Mott transition”
Physical picture of 1D exciton–plasma transition
the exciton Mott transition
Increase of e–h pair density causes
・ reduction of exciton binding energy
・ red shift of the band edge
(band-gap renormalization (BGR))
eg. D. W. Wang and S. Das Sarma,
PRB 64, 195313 (2001).
Our PL results show
 no energy shift of the exciton
band edge
 plasma low-energy edges appear
at the bi-exciton energy positions,
and show BGR
 no connection, but coexistence
of two band edges
band edge
exciton level
no level-crossing between the band
edges and the exciton level
Exciton band edge & plasma band edge (T=30K)
▼ plasma band edge
(low energy edge of plasma PL)
starts at biexciton energy
and shows red shift.
▼ exciton band edge,
(onset of continuum states)
exciton ground and excited states
show no shift.
Electron plasma
and minority hole
eeeeheeeee
e he
X- Charged Exciton
X Exciton
eh
Theory
1D exciton and continuum states
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