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 Tok yo and CREST, JST L. N. Pfeiffer, K. W. West, and Ibo Matthews Bell Laboratories, Lucent Technologies 2004 Fall MRS meeting in Boston (2004.11.30 B3. tion of high-quality GaAs T-shaped quantum wires leaved-edge overgrowth with MBE, AFM, PL, PLE e-wire laser L scan, Lasing, PL, Absorption/Gain via Cassidy’s method, Tra vation of RT 1D exciton absorption in 20-wire laser al response of n-doped single-wire FET device
Transcript
T-shaped quantum-wire laserM. 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 MatthewsBell Laboratories, Lucent Technologies
2004 Fall MRS meeting in Boston (2004.11.30 B3.1)
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
Absorption/gain measurement based on Hakki-Paoli-Cassidy’s analysis of Fabry-Perot-laser emission below threshold
Free Spectral Range
Point
Absorption Spectrum by Cassidy method
Excitation Light ： cw TiS laser at 1.631eV
WaveguideEmission
Polarizationparallel toArm well
Spectrometer with spectral resolution of
0.15 meV
Cassidy’s Method
Single wire laser, uncoated cavity mirrors
Excitation Light ： cw TiS laser at 1.631eV
WaveguideEmission
Polarizationparallel toArm well
Stripe shape
Spectrometer with spectral resolution of
0.15 meV
Spontaneousemission
Measurement of absorption/gain spectrum
Cassidy’s Method
8.3mW
Absorption/gain spectrum (High excitation power)
Electron-Hole Plasma
EFEEBE
Gain
Absorption
Hayamizu et al.
8.3mW
1. Exciton peak and continuum onset decay without shift.
2. Gap between exciton and continuum is gradually filled.
3. Exciton changes to Fermi edge
Electron-Hole Plasma
ExcitonHayamizu et al.
Transmission measurementof a single quantum wire
~nmm
Transmittance for single
Takahashi et al. unpublished
Coupling efficiency
= 20%
Absorption for single
Takahashi et al. unpublished
Absorption for 20
Y. Takahashi et al.
Absorption at 300 K
Y. Takahashi et al.
Room-Temperature 1D Exciton Absorption!
1D
ele
ctro
n d
en
sity
14nmx6nm Doped Single Wire FET device with tunable 1D electr
on density
ehe
e hT. Ihara et al.
Quantum-Wire Devices
Summary
1. GaAs T-shaped quantum wires (T-wires) are formed by cleaved-edge overgrowth with MBE.
2. Growth-interrupt anneals dramatically improve T-wire quality.3. AFM : No atomic steps over 100m.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 / 500m) 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) (110)
[001]
[110]
[110]
[001]
Growth rate of GaAs in MBE
Substrate rotation >>> uniform
Ga limited growth under
As4 overpressure
490oC GrowthHigh Quality
T-wire
Interface control by growth-interruption annealing
(by M. Yoshita et al.
JJAP 2001)
Atomically flat
interfaces
600oC Anneal
armwell6nm
stemwell14nm
(By Yoshita et al. APL 2002)
Single wire laser with 500m 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) Lasing in excited-states of V-wiresW. Wegscheider et al. Lasing in the ground-state of T-wires, no energy shift, (PRL’93) excitonic lasingR. Ambigapathy et al. PL without BGR, strong excitonic effect in V-wires (PRL’97) L. Sirigu et al. (PRB’00) Lasing due to localized excitons in V-wiresJ. Rubio et al. (SSC’01) Lasing observed with e–h plasma emission in T-wiresA. Crottini et al. (SSC’02) PL from exciton molecules (bi-excitons) in V-wiresT. Guillet et al. (PRB’03) PL, Mott transition form excitons to a plasma in V-wiresH. Akiyama et al. Lasing due to e–h plasma, no exciton lasing in T-wires
(PRB’03)
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)
Theories
“1D exciton Mott transition”
eg. D. W. Wang and S. Das Sarma, PRB 64, 195313 (2001).
・ reduction of exciton binding energy
・ red shift of the band edge (band-gap renormalization (BGR))
Physical picture of 1D exciton–plasma transition
Increase of e–h pair density causes
the exciton Mott transition Our PL results show
band edge
exciton level
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
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 statesshow no shift.
