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

T-shaped Quantum Wire (T-wire)

Cleaved-edge overgrowth with MBE

Cleavein situ

(001) MBE Growth (110) MBE Growth

[110]

[001]

GaAssubstrate

600oC 490oC

by L. N. Pfeiffer et al., APL 56, 1679 (1990).

(490oC)

Good

Poor

Bad

Nomarski MicroscopeImages ofCleaved-Edge-OvergrowthSurfaces

“Hackling”

490C Growth

(By Yoshita et al. JJAP 2001)

Atomically flat

interfaces

High Quality

T-wire ???

490C Growth

(By Yoshita et al. JJAP 2001)

Atomically flat

interfaces

High Quality 510-600C Anneal

T-wire !?

490C Growth

(By Yoshita et al. JJAP 2001)

Atomically flat

interfaces

High Quality 510-600C Anneal

T-wire !!?

490C Growth

(By Yoshita et al. JJAP 2001)

Atomically flat

interfaces

High Quality 510-600C Anneal

T-wire !!!!!

1st growth

600C

2nd growth

490C (arm well)

600C 10min anneal

490C (cover layers)

Laser bars

500m uncoated cavity

20-wire laser sample14nm x 6nm

(Akiyama et al. APL 2003)

PL and PLEspectra

Sharp PL width

Small Stokes shift

1D free exciton

1D continuum states

armwell

stemwell

T-wire

E-field

// to wire

_ to wire// to arm wellI

E-field

Cavity length 　 500 m

Probability of Photon

Probability of Electron

Single quantum wire laser

=5x10-4

Scanning micro-PL spectra

ContinuousPL peak over 20 m

PL width < 1.3 meV

scan

T=5K

T-wire T-wirestem well stem well

500m gold-coated cavity

Threshold 5mW

(Hayamizu et al, APL 2002)

Lasing in a single quantum wire

Excitation power dependence of PL

M. Yoshita, et al.

Free Exciton

Biexciton+Exciton

Electron-hole Plasma

Den

sit

y

n1D = 3.6 x 103 cm-1 (rs = 220 aB)

n1D = 1.2 x 105 cm-1 (rs = 6.6 aB)

n1D = 1.2 x 106 cm-1

(rs = 0.65 aB)

n1D ~ 102 cm-1

aB ~13nm

EB =2.8meV

θee

eE

ll

l

I22

2

sinR4)R1(

R)1(A)(

B. W. Hakki and T. L. Paoli JAP. 46 1299 (1974)

11

R1

ln1pp

l

min

sum/FSR

I

Ip

R ：Reflectivity

c

Eln

： Absorption coeff.

D. T. Cassidy JAP. 56 3096 (1984)

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.

X- Charged Exciton

X Exciton

Electron plasmaand minority hole

e h

ehe

eheeeeeeee

Theory1D exciton and continuum states