stem electron density ~ 1×10 11 cm -2 gate voltage ( vg ) 0.0 ~ 0.8v wire electron...
TRANSCRIPT
stem electron density ~ 1×1011 cm-2
Gate Voltage ( Vg ) 0.0 ~ 0.8V
wire electron density
0 ~ 4×105 cm-
1
arm electron density
0 ~ 1.3×1011 cm-
2
Sample
1.5681.5641.560
Photon Energy (eV)
Phot
olumi
nesc
ence
Inte
nsity
(arb
.unit)
1.5701.5651.560Photon Energy (eV)
1μm step0.2μm step scanScan 1• Micro PL measurement with 1
μm / 0.2μm step automatic scanning enables us to find the center (blue circle) at every experiments.
Photon Energy (eV)
• Gate Voltage = 0.1V
• T=5K
• Stem well excitation with cw Ti:Sa laser (λ=750nm ) 0.2μW 、~1μm2 spot size
• Reflection geometry
• Resolution 0.15meV
wire trion PL
Phot
olumi
nesc
ence
Inte
nsity
(arb
.unit)
1.5901.5801.5701.560
Photon Energy (eV)
Phot
olum
ines
cenc
e In
tens
ity (a
rb.u
nit)
1.5901.5801.5701.560
Photon Energy (eV)
Phot
olum
ines
cenc
e In
tens
ity (a
rb.u
nit)
1.5901.5801.5701.560
Photon Energy (eV)
Scan 2 arm excitonwire trionGate Voltage = 0.1Vcheck all available aria with
~500μm ( 1.0μm step ) scanningPL
con
tinue m
ore
than
co
ntin
ue m
ore
than
5
00
μm
…5
00
μm
…
1.5701.5651.560Photon Energy (eV)
1.5701.5651.560Photon Energy (eV)
1.5701.5651.560Photon Energy (eV)
Phot
olum
ines
cenc
e In
tens
ity (a
rb.u
nit)
1.5701.5651.560Photon Energy (eV)
Vg=0.7V Vg=0.5V Vg=0.3V Vg=0.1V
0.5μm step scanning withvarious Gate Voltage ( Vg )scan 3
Photon Energy (eV)
→ find the high quality aria (for example : blue arrow)
T=5K
PL
Phot
olum
ines
cenc
e In
tens
ity (a
rb.u
nit)
1.5701.5651.560
Photon Energy (eV)
Gate Voltage dependenceVg = 0V ~ 0.7V (0.05V
step)
corresponds
n1D = 0 ~ 4×105cm‐1
EFE = 0~1.8meV
①②
③
⑤④
①low electron density
→1.569eV exciton peak②trion peak : 2.3meV below exciton peak
(trion binding energy)
③high density → band to band transition 、 electron plasma state
④Band Gap Renormalization(BGR)
⑤Fermi Edge Singularity(FES)
T=5KPL
1.5701.5651.560Photon Energy (eV)
1.5701.5651.560Photon Energy (eV)
1.5701.5651.560Photon Energy (eV)
Pho
tolu
min
esce
nce
Inte
nsity
(arb
.uni
t)
1.5701.5651.560Photon Energy (eV)
Temperature dependence
T=50K T=40K T=30K
Photon Energy (eV)
T=5K
①BGR at every temperature②ratio of exciton / trion peak
become large with temperature③FES disappear at high temperature
①①① ①
②②
③③
1.567
1.566
1.565
1.564
1.563
Pho
ton
Ener
gy (eV
)
0.80.60.40.20.0
Gate Voltage (V)1.5701.5651.560
Photon Energy (eV)1.5701.5651.560
Photon Energy (eV)1.5701.5651.560
Photon Energy (eV)
Pho
tolu
min
esce
nce
Inte
nsity
(arb
.uni
t)
1.5701.5651.560Photon Energy (eV)
Temperature dependence of Energy shift compare BGR at Gate Voltage 0.2V~0.7V
5K
30K
40K
50K
Photon Energy (eV)
T (K) BGR(meV)
5 2.1
30 1.4
40 1.4
50 1.0
Small BGR at high temperature① ① ① ①
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
FWHM
(meV
)
0.80.60.40.20.0
Gate Voltage (V)
・ trion peak ( Vg=0.2 ~0.3V )
Temperature dependence of FWHM
5K
30K
40K
50K
Photon Energy (eV)1.5701.5651.560
Photon Energy (eV)1.5701.5651.560
Photon Energy (eV)1.5701.5651.560
Photon Energy (eV)
Pho
tolu
min
esce
nce
Inte
nsity
(arb
.uni
t)
1.5701.5651.560Photon Energy (eV) Photon Energy (eV)
T (K) FWHM(meV)
5 ~ 0.7
30 ~ 1.5
40 ~ 2.0
50 ~ 2.3
・ At high Gate Voltage (Vg=0.4V~)
temperature dependence of FWHM is very small④ ④ ④ ④
1.55 1.57 1.59 1.61 1.63 1.65
wire HH
PLE
PL
PL & PLE of wire
stem LH
stem HH
arm HH
Photon Energy (eV)
arm LH
PL
and
PLE
Inte
nsity
(ar
b.un
its)
1.5721.5681.564
Photon Energy (eV)
PL detection is perpendicular to the laser excitation to improve S/N ratio.Vg = 0.15V T = 5K
LH : light hole
HH : heavy hole
excitation
detect
polarization
PL
and
PLE
Int
ensi
ty (
arb.
units
)
1.5721.5701.5681.566
Photon Energy (eV)
0.0V
0.1V
0.15V
0.2V
0.3V
0.4V
①
②
③
①neutral exciton
(exciton)
②charged exciton
(trion)
③FES
PL
and
PLE
Int
ensi
ty (
arb.
units
)
1.5721.5701.5681.566
Photon Energy (eV)Photon Energy (eV)
Low density PLEPL
③
Gate Voltage 0.0V ~ 0.4V
Theoretical work : M. Takagiwa, T. Ogawa, 2001
density
density
nn1D1D
HH
LL
PL
and
PLE
Inte
nsity
(arb
.uni
ts)
1.5761.5721.5681.564
Photon Energy (eV)
PL
and
PLE
Inte
nsity
(arb
.uni
ts)
1.5761.5721.5681.564
Photon Energy (eV)
0.25V
0.35V
0.4V
0.5V
0.6V
0.7V
0.15V①Fermi Edge
②Band Edge
③ ???
①②
③High density
Photon Energy (eV)
PLEPL
Gate Voltage
0.4V ~ 0.7V
electron plasma
Electron density dependence of PLE varies with the position of the wire.
PLE trion→electron plasma
1.564 1.566 1.568 1.57 1.572
0.30.350.40.450.5PL
1.564 1.566 1.568 1.57 1.572 1.564 1.566 1.568 1.57 1.572
Photon Energy [eV]
PL a
nd P
LE i
nten
sity
[arb
. Uui
ts] ( PLE )
Vg = 0.3V
Vg = 0.35V
Vg = 0.4V
Vg = 0.45V
Vg = 0.5V
( PL )
Vg = 0.15V
PL
and
PLE
Int
ensi
ty (
arb.
units
)
1.5761.5721.5681.564
Photon Energy (eV)
PLE
PL
PLE
PL
PLE
PL
1.564 1.565 1.566 1.567 1.568 1.569 1.57 1.571 1.572
PLE ( Vg=0.15 ) and PL ( Vg=0.12 ) at different position of wire.
Resolution of PL : 0.15meV, PLE : 0.04meV 。
The gap between exciton peaks (or trion peaks) varies with electron density from 0.3meV to 0.5meV. This is probably due to stem well ML fluctuation (theoretical calculation : stem well ML fluctuation is ~0.3meV).
High resolution PLE
1.564 1.565 1.566 1.567 1.568 1.569 1.57 1.571 1.572
1.564 1.565 1.566 1.567 1.568 1.569 1.57 1.571 1.5721.564 1.565 1.566 1.567 1.568 1.569 1.57 1.571 1.572
PL a
nd P
LE i
nten
sity
[arb
. Uui
ts]
Photon Energy [eV]Photon Energy [eV]
PLEPL
PL
and
PLE
Int
ensi
ty (
arb.
units
)
1.5701.5681.566
Photon Energy (eV)
0.0V
0.02V
0.04V
0.06V
0.08V
0.14V
0.10V
0.12V
Exciton peak shifts with electron density : 3.5meV / V ( blue line ).
FWHM of PL spectrum (corresponds EF) changes ~ 3.5meV/V.
Trion peak doesn’t shift. Equation below can be
expected.
exciton shift
Fb EE 12
PLE
trion exciton2
1: exciton: trion
PL
and
PLE
Int
ensi
ty (
arb.
units
)
1.5761.5721.5681.564
Photon Energy (eV)
PL a
nd P
LE In
tens
ity (a
rb.u
nits
)
1.5881.5841.580
Photon Energy (eV)
1.1
0.8
0.2
1.5
1.8
2D ( arm well ) / 1D well
①①
②
②
③
③ 0.5
wire EF
( meV)
1.1
0.8
0.2
1.5
1.8
0.5
EF
( meV)
④ ④① Eb
wire : Eb=2.3meV
well : Eb=1.4meV
② wire : blue shift, rapid dampingwell : blue shift, broadening
③trionabsorp
wire : no shift, rapid dampingwell : blue shift, broadening
④ wire : large blue shiftwell : small blue shift begins from trion peak smoothly
excitonAbsorp.
plasmaabsorp.
V. Huard et al. Phys. Rev. Lett. 84 (2000) 187