Photoluminescence-excitation spectraPhotoluminescence-excitation spectraonon

n-type doped quantum wiren-type doped quantum wire

ISSP Akiyama group D1 Toshiyuki Ihara

05.12.16 　 seminar ＠ ISSP with Kono group

IntroductionIntroduction 　　～～　　 One dimensional One dimensional systemsystem

Inverse-square-root divergence Density of state (DOS)

EED D /1)(1

Interesting phenomena appear!!・ Large exciton binding energy.

・ Strong absorption of

exciton groundstate.

・ High speed optical modulation device.

・ High performance laser device.

Background Background ～～ calculation for doped 1D systemcalculation for doped 1D system

Rodriguez et al., Phys. Rev. B 47, 1506 (1993)

“1D DOS singularity” and/or “Fermi edge singularity” would appear.

Band bottom Fermi edge

absorption

emission

＜ Theoretical calculation by Rodriguez et. al. ＞

Dotted line non-interacting free particle

Solid line includes many-body effect (Fermi edge singularity)

BackgroundBackground 　　～～　 　 experiments of doped 1D system experiments of doped 1D system ①①

Calleja et al., Solid State Commun. 79, 911 (1991) Oberli et al., Physica E 11, 224 (2001)

Doped multi V-groove wiresDoped multi well-wires

Strong FES effect Weak FES effect

BackgroundBackground 　　～～　 　 experiments of doped 1D system experiments of doped 1D system ②②

Htoon et al., Phys. Rev. Lett. 93, 027401 (2004)Akiyama et al., Solid State Commun. 122, 169 (2002)

Doped single T-wire Doped nanotube

What causes strong FES effect ? Where is 1D DOS singularity ?

Weak FES effect

Strong FES effect

MotivationMotivation ～ ～ optical absorption of doped quantum wireoptical absorption of doped quantum wire

For the observation of 1D density of state …

・ High-quality・ 1D limit・ direct gap structure

Our T-shaped wire meet these conditions !!

Furthermore, in order to obtain absorption spectra …

We developed “High resoluted photoluminescence-excitation (PLE) method”

PLE spectra of ground state of single quantum wire are possible to obtain !!

Sample structureSample structure＜ fabrication ＞

MBE with cleaved edge overgrowth method

＜ size of wire ＞

14 x 6nm x 4mm(single)

＜ doping ＞

①Si modulation doping②FET gate structure→tunable electron density

＜ measurement ＞

Polarization selected micro-PL & PLE spectra

PL and PLE overviewPL and PLE overview

A clear PLE peak of wire ground state was obtained.

stokes shift ＜ 0.2meV

How the “wire” peak changes with increasing electron density !?

Results for 1D systemResults for 1D system

Metal-insulator crossover of 1D doped system was observed for the first time.

＜ interesting results ＞

①double peak structure at the metal-insulator

crossover region.

②remarkable quenching of exciton peak

②

①

※hole density is small

What is the origin of double peak ?

Free particle calculationFree particle calculation

/1)(1 DjD

Effective mass 2 band model、　 Fermi distribution of electron gas

absorption

emission dELffDI ghhee

Dj 1

dELfDA geeD

j 11

he

= 0.2meVTe = Th = 8K

ehe mm )/1(

eee

e

ee df

mn

121

2

ComparisonComparison

good agreement for PLE at high electron density!!

Double peak structure ① corresponds to “1D DOS singularity” and “Fermi edge”.

②

①

FES effect is not strong.

High density and High temperatureHigh density and High temperature

BE 　： Band Edge 　

FE 　： Fermi Edge

Sharp absorption peak of at 50K corresponds to 1D DOS singularity !!

= 0.5meVTe = Th

BE

Calculation parameter

Results for 2D systemResults for 2D system Same results as other groups・ Finkelstein et al., Phys. Rev. Lett. 74, 976 (1995)・ Huard et al., Phys. Rev. Lett. 84, 187 (1999)・ Yusa et al., Phys. Rev. B 62, 15390 (2000)・ Kaur et al., Phys. Status Solidi B 178, 465 (2000)・ Cox et al., Phys. Rev. B 69, 235303 (2004)

Band edge absorption is not sharp peak but step-function onset

ConclusionConclusionWe measured PLE spectra at low temperature on an n-type doped single

quantum wire with a gate to tune electron densities.

①A double peak structure corresponding 1D DOS singularity and Fermi edge appeared.

②exciton peak quenches at low density 　 (1×105cm1 )

Study the effect of hole localization on the Fermi edge singularity

by Carbon-acceptor doped quantum wire

＜ Further investigation ＞