Electron Density Dependence of Optical Spectroscopy of Single GaAs Quantum Wire
We demonstrate one-dimensional (1D) optical properties in photoluminescence (PL) and
photoluminescence excitation (PLE) in an n-type-modulation-doped single GaAs
quantum wire of superior quality. The sample was grown by the cleaved-edge
overgrowth (CEO) method with molecular beam epitaxy (MBE). The wire size is 14nm x
6nm. We tune the electron density with application of an external electric field from
zero to almost 4×10 cm
5
1
[1]. The sample is excited by a tunable Ti-Sapphire laser.
We recorded a set of PLE and the corresponding PL spectra for various gate voltages.
We observed the appearance of one-dimensional excitons (1.569 eV) and negatively
charged excitons (2.3 meV below exciton peak energy) absorption at low temperature
(5K).
At low density, emission and absorption of neutral exciton is dominant. Both PL and
PLE peak FWHM is 1.1meV and stokes shift is small. As the electron density become
higher, neutral exciton PL and PLE peak become weak and charged exciton appears and
become strong. Both exciton and charged exciton absorption line shape become
asymmetrical (a fast rise at the low-energy side and a slow fall at high energies). This is
similar to Fermi Edge Singularity in 2D quantum well optical absorption spectrum [2].
This effect might be observed in 1D electron-hole system[3], but there are few
experimental reports.
When the density reaches almost 2.5×10 cm
5
1
, Band-to-band transition begins and PL
line shape become broad. On the other hand the absorption edge become unclear with
increased electron plasma density. At high density above 2.5×10 cm
5
1
, we observed a
large red-shift (2.9meV) and broadening of PL with increased electron plasma density.
Shrinkage of the optical band-gap with electron plasma due to the many-body Coulomb
interaction is called band-gap renormalization (BGR).
[1] H. Akiyama et al., Solid. State. Commun. 122 169 (2002).
[2] G. Yusa et al., Phys. Rev. Lett. 62, 15390 (2000).
[3] T. Ogawa et al., Phys. Rev.Lett 68, 3638 (1992).
Institute for Solid State Physics, University of Tokyo, CREST( JST), Kashiwa, Chiba,
Japan
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
Yuhei Hayamizu, Hirotake Itoh, Masahiro Yoshita and Hidefumi Akiyama
Institute for Solid State Physics, University of Tokyo, CREST, JST
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
Loren N. Pfeiffer and Ken W. West
Bell Laboratories, Lucent Technologies, 600 Mountain Avenue,
Murray Hill, NJ 07974, USA
Photoluminescence excitation spectra of one-dimensional electron systems in an n-type
doped quantum wire
We
measured
photoluminescence
(PL)
and
PL excitation
(PLE) spectra
of
one-dimensional (1D) excitons, charged excitons, and an electron plasma in a
high-quality n-type-modulation-doped single GaAs quantum wire with a gate, where
density of 1D electron gas is tuned by gate voltage. We demonstrate that the absorption
line shape of the charged excitons varies gradually from symmetric to asymmetric with
electron density in the wire, which then changes to a shoulder corresponding to an
absorption onset of an electron-plasma system. The high-energy tail of the asymmetric
absorption line of the charged excitons is analogous to a power-law anomaly appearing
in Fermi-edge singularity (FES) studied more in detail in two-dimensional (2D)
quantum wells [1,2], and reflects many-body electron interactions in this system.
The sample is T-shaped quantum wire grown by the cleaved-edge overgrowth method
with molecular beam epitaxy [3]. The wire size is 14nm x 6nm. We changed gate voltage
to tune the electron density from zero (0V) to almost 4×10 cm
5
1
(0.8V) [4]. The sample
is excited by a tunable Ti-Sapphire laser. The direction of detection is perpendicular to
laser direction to improve signal-to-noise ratio. We recorded sets of photoluminescence
excitation (PLE) spectra and the corresponding PL spectra for various gate voltages at
low temperature (5K)
At low density, PL and PLE peak of the neutral excitons (1.569 eV) is dominant. Both
PL and PLE peak FWHM are 1.1meV and the stokes shift is small. The PLE line shape
seems symmetrical.
As electron density become higher, the PL and PLE peak of the neutral excitons become
weak and the peak of the charged excitons appears and becomes strong at 2.3 meV
below the peak energy of the excitons. When the electron density reaches almost 1×
10 cm
5
1
(0.15V), both neutral excitons and charged excitons PLE line shape become
asymmetrical (a fast rise at the low-energy side and a slow fall at high energies). The
power-law singularity of the high-energy tail indicates FES of 1D system.
Above 1×10 cm
5
1
, the PL and PLE line shape of the charged excitons become broad
due to band-to-band transition. At high density above 2.5×10 cm
5
1
(0.3V), the red-shift
of the PL peak energy due to Band-Gap Renormalization begins and the PLE edge
become unclear.
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
[2] M. Takagiwa and T. Ogawa,J. Phys. Chem. Solids. 63 (2002) 1587
[3] L. N. Pfeiffer, K. W. West. H. L. Stormer, J. P. Eisenstein, K. W. Baldwin, D. Gershoni,
and J. Spector, Appl. Phys. Lett. 56 (1990) 1697
[4] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid. State.
Commun. 122 (2002) 169.
Photoluminescence excitation spectra of one-dimensional electron systems in an n-type
doped quantum wire
We
measured
photoluminescence
(PL)
and
PL excitation
(PLE) spectra
of
one-dimensional (1D) excitons, charged excitons, and an electron plasma in a
high-quality n-type-modulation-doped single GaAs quantum wire with a gate, where
density of 1D electron gas is tuned by gate voltage. We demonstrate that the absorption
line shape of the charged excitons varies gradually from symmetric to asymmetric with
electron density in the wire, which then changes to a shoulder corresponding to an
absorption onset of an electron-plasma system. The high-energy tail of the asymmetric
absorption line of the charged excitons is analogous to a power-law anomaly appearing
in Fermi-edge singularity (FES) studied more in detail in two-dimensional (2D)
quantum wells [1,2], and reflects many-body electron interactions in this system.
The sample is T-shaped quantum wire grown by the cleaved-edge overgrowth method
with molecular beam epitaxy [3]. The wire size is 14nm x 6nm. We changed gate voltage
to tune the electron density from zero (0V) to almost 4×10 cm
5
1
(0.8V) [4]. The sample
is excited by a tunable Ti-Sapphire laser. The direction of detection is perpendicular to
laser direction to improve signal-to-noise ratio. We recorded sets of photoluminescence
excitation (PLE) spectra and the corresponding PL spectra for various gate voltages at
low temperature (5K)
At low density, PL and PLE peak of neutral excitons (1.569 eV) is dominant. Both PL
and PLE peak FWHM are 1.1meV and stokes shift is small. The PLE line shape seems
symmetrical.
As electron density become higher, the PL and PLE peak of the neutral excitons become
weak and a peak of charged excitons appears and becomes strong at 2.3 meV below the
peak energy of excitons. When electron density reaches almost 1×10 cm
5
1
(0.15V),
both neutral excitons and charged excitons PLE line shape become asymmetrical (a fast
rise at the low-energy side and a slow fall at high energies). The power-law singularity
of the high-energy tail indicates FES of 1D system.
Above 1×10 cm
5
1
, PL and PLE line shape of the charged excitons becomes broad due
to band-to-band transition. At high density above 2.5×10 cm
5
1
(0.3V), red-shift of the
PL peak energy due to Band-Gap Renormalization begins and the PLE edge become
unclear.
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
[2] M. Takagiwa and T. Ogawa, to be published.
[3] L. N. Pfeiffer, K. W. West. H. L. Stormer, J. P. Eisenstein, K. W. Baldwin, D. Gershoni,
and J. Spector, Appl. Phys. Lett. 56 (1990) 1697
[4] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid. State.
Commun. 122 (2002) 169.
Photoluminescence excitation spectra of one-dimensional electron systems in an n-type
doped quantum wire
We
measured
photoluminescence
(PL)
and
PL excitation
(PLE) spectra
of
one-dimensional (1D) excitons, charged excitons, and an electron plasma in a
high-quality n-type-modulation-doped single GaAs quantum wire with a gate, where
density of 1D electron gas is tuned by gate voltage. We demonstrate that the absorption
line shape of the charged excitons varies gradually from symmetric to asymmetric with
electron density in the wire, which then changes to a shoulder corresponding to an
absorption onset of an electron-plasma system. The high-energy tail of the asymmetric
absorption line of the charged excitons is analogous to a power-law anomaly appearing
in Fermi-edge singularity (FES) studied more in detail in two-dimensional (2D)
quantum wells [1,2], and reflets many-body electron interactions in this system.
The sample is T-shaped quantum wire grown by the cleaved-edge overgrowth method
with molecular beam epitaxy [3]. The wire size is 14nm x 6nm. We changed gate voltage
to tune the electron density from zero (0V) to almost 4×10 cm
5
1
(0.8V) [4]. The sample
is excited by a tunable Ti-Sapphire laser. The direction of detection is perpendicular to
laser direction to improve signal-to-noise ratio. We observed PL and PLE of neutral
exciton, charged exciton and electron plasma at low temperature (5K)
At low density, PL and PLE peak of neutral exciton (1.569 eV) is dominant. Both PL
and PLE peak FWHM is 1.1meV and stokes shift is small. The PLE line shape seems
symmetrical. As the electron density become higher, PL and PLE peak of neutral
exciton becomes weak and peak of charged exciton appears and becomes strong at 2.3
meV below peak energy of exciton.
When the density reaches almost 1×10 cm
5
1
(0.15V), both neutral exciton and
charged exciton PLE line shape become asymmetrical (a fast rise at the low-energy side
and a slow fall at high energies). The FWHM of PLE peak become more than twice
though the peak energy is almost same. The power-law singularity of the tail indicates
FES of 1D system. Above 1×10 cm
5
1
, PL and PLE line shape of charged exciton
becomes broad due to band-to-band transition. At high density above 2.5 ×
10 cm
5
1
(0.3V), red-shift of PL peak energy due to Band-Gap Renormalization begins
and the PLE edge become unclear.
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
[2] M. Takagiwa and T. Ogawa, to be published.
[3] L. N. Pfeiffer, K. W. West. H. L. Stormer, J. P. Eisenstein, K. W. Baldwin, D. Gershoni,
and J. Spector, Appl. Phys. Lett. 56 (1990) 1697
[4] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid. State.
Commun. 122 (2002) 169.
Photoluminescence excitation spectra of one-dimensional electron systems in an n-type
doped quantum wire
We
measured
photoluminescence
(PL)
and
PL excitation
(PLE) spectra
of
one-dimensional (1D) excitons, charged excitons, and an electron plasma in a
high-quality n-type-modulation-doped single GaAs quantum wire with a gate, where
density of 1D electron gas is tuned by gate voltage. We demonstrate that the absorption
line shape of the charged excitons varies gradually from symmetric to asymmetric with
electron density in the wire, which then changes to a shoulder corresponding to an
absorption onset of an electron-plasma system. The high-energy tail of the asymmetric
absorption line of the charged excitons is caused by many-body electron interactions in
this system, since it is analogous to a power-law anomaly appearing in Fermi-edge
singularity (FES) studied more in detail in two-dimensional (2D) quantum well [1,2].
The sample is T-shaped quantum wire grown by the cleaved-edge overgrowth method
with molecular beam epitaxy [3]. The wire size is 14nm x 6nm. We changed gate voltage
to tune the electron density from zero (0V) to almost 4×10 cm
5
1
(0.8V) [4]. The sample
is excited by a tunable Ti-Sapphire laser. The direction of detection is perpendicular to
laser direction to improve signal-to-noise ratio. We observed PL and PLE of neutral
exciton, charged exciton and electron plasma at low temperature (5K)
At low density, PL and PLE peak of neutral exciton (1.569 eV) is dominant. Both PL
and PLE peak FWHM is 1.1meV and stokes shift is small. The PLE line shape seems
symmetrical. As the electron density become higher, PL and PLE peak of neutral
exciton becomes weak and peak of charged exciton appears and becomes strong at 2.3
meV below peak energy of exciton.
When the density reaches almost 1×10 cm
5
1
(0.15V), both neutral exciton and
charged exciton PLE line shape become asymmetrical (a fast rise at the low-energy side
and a slow fall at high energies). The FWHM of PLE peak become more than twice
though the peak energy is almost same. The power-law singularity of the tail indicates
FES of 1D system. Above 1×10 cm
5
1
, PL and PLE line shape of charged exciton
becomes broad due to band-to-band transition. At high density above 2.5 ×
10 cm
5
1
(0.3V), red-shift of PL peak energy due to Band-Gap Renormalization begins
and the PLE edge become unclear.
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
[2] M. Takagiwa and T. Ogawa, to be published.
[3] L. N. Pfeiffer, K. W. West. H. L. Stormer, J. P. Eisenstein, K. W. Baldwin, D. Gershoni,
and J. Spector, Appl. Phys. Lett. 56 (1990) 1697
[4] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid. State.
Commun. 122 (2002) 169.
Photoluminescence excitation spectra of one-dimensional electron system in an n-type
doped quantum wire
We observed the symmetrical absorption line shape of charged exciton becomes
asymmetrical gradually with electron density. And the absorption edge becomes unclear
due to electron plasma at high electron density. The asymmetrical absorption line shape
was observed clearly in two-dimensional (2D) quantum well [1] and is theoretically
calculated in 1D system [2]. This effect is called Fermi edge singularity (FES), the tail of
the absorption spectrum should exhibit a power-law singularity.
We recorded micro-photoluminescence (PL) and photoluminescence excitation (PLE)
in an n-type-modulation-doped single GaAs quantum wire of superior quality. The
sample is T-shaped quantum wire grown by the cleaved-edge overgrowth method with
molecular beam epitaxy [3]. The wire size is 14nm x 6nm. We changed gate voltage to
tune the electron density from zero (0V) to almost 4×10 cm
5
1
(0.8V) [4]. The sample is
excited by a tunable Ti-Sapphire laser. The direction of detection is perpendicular to
laser direction to improve signal-to-noise ratio. We observed PL and PLE of neutral
exciton, charged exciton and electron plasma at low temperature (5K)
At low density, PL and PLE peak of neutral exciton (1.569 eV) is dominant. Both PL
and PLE peak FWHM is 1.1meV and stokes shift is small. The PLE line shape seems
symmetrical. As the electron density become higher, PL and PLE peak of neutral
exciton becomes weak and peak of charged exciton appears and becomes strong at 2.3
meV below peak energy of exciton.
When the density reaches almost 1×10 cm
5
1
(0.15V), both neutral exciton and
charged exciton PLE line shape become asymmetrical (a fast rise at the low-energy side
and a slow fall at high energies). The FWHM of PLE peak become more than twice
though the peak energy is almost same. The power-law singularity of the tail indicates
FES of 1D system. Above 1×10 cm
5
1
, PL and PLE line shape of charged exciton
becomes broad due to band-to-band transition. At high density above 2.5 ×
10 cm
5
1
(0.3V), red-shift of PL peak energy due to Band-Gap Renormalization begins
and the PLE edge become unclear.
[1] G. Yusa, H. Shtrikman, and I. Bar-Joseph, Phys. Rev. B 62 (2000) 15390.
[2] M. Takagiwa and T. Ogawa, to be published.
[3] L. N. Pfeiffer, K. W. West. H. L. Stormer, J. P. Eisenstein, K. W. Baldwin, D. Gershoni,
and J. Spector, Appl. Phys. Lett. 56 (1990) 1697
[4] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid. State.
Commun. 122 (2002) 169.
東大物性研、CREST(JST)、ルーセント・ベル研 A
井原章之、早水裕平、吉田正裕、秋山英文、Loren N. PfeifferA、Ken W. WestA
Photoluminescence and Photoluminescence Excitation Spectra in
a n-type doped
quantum wire
ISSP, Univ. of Tokyo, CREST(JST) and Bell Labs., Lucent TechnologiesA
T. Ihara, Y. Hayamizu, M. Yoshita, H. Akiyama,
L. N. PfeifferA, and K. W. WestA
Electron Density Dependence of Optical Spectroscopy of Single GaAs Quantum Wire
We demonstrate one-dimensional (1D) optical properties in photoluminescence (PL) and
photoluminescence excitation (PLE) in an n-type-modulation-doped single GaAs
quantum wire of superior quality. The sample was grown by the cleaved-edge
overgrowth (CEO) method with molecular beam epitaxy (MBE). The wire size is 14nm x
6nm. We tune the electron density with application of an external electric field from
zero to almost 4×10 cm
5
1
[1]. The sample is excited by a tunable Ti-Sapphire laser.
We recorded a set of PLE and the corresponding PL spectra for various gate voltages.
We observed the appearance of one-dimensional excitons (1.569 eV) and negatively
charged excitons (2.3 meV below exciton peak energy) absorption at low temperature
(5K).
At low density, emission and absorption of neutral exciton is dominant. Both PL and
PLE peak FWHM is 1.1meV and stokes shift is small. As the electron density become
higher, neutral exciton PL and PLE peak become weak and charged exciton appears and
become strong. Both exciton and charged exciton absorption line shape become
asymmetrical (a fast rise at the low-energy side and a slow fall at high energies). This is
similar to Fermi Edge Singularity in 2D quantum well optical absorption spectrum [2].
This effect might be observed in 1D electron-hole system[3], but there are few
experimental reports.
When the density reaches almost 2.5×10 cm
5
1
, Band-to-band transition begins and PL
line shape become broad. On the other hand the absorption edge become unclear with
increased electron plasma density. At high density above 2.5×10 cm
5
1
, we observed a
large red-shift (2.9meV) and broadening of PL with increased electron plasma density.
Shrinkage of the optical band-gap with electron plasma due to the many-body Coulomb
interaction is called band-gap renormalization (BGR).
[1] H. Akiyama et al., Solid. State. Commun. 122 169 (2002).
[2] G. Yusa et al., Phys. Rev. Lett. 62, 15390 (2000).
[3] T. Ogawa et al., Phys. Rev.Lett 68, 3638 (1992).
[2] T. Ogawa et al., Phys. Rev.Lett 68, 3638 (1992).
[2]
We observed the appearance of one-dimensional excitons (1.569 eV) and negatively
charged excitons (2.3 meV below exciton peak energy) absorption at low temperature
(5K).
At low density, emission and absorption of neutral exciton is dominant. Both PL and
PLE peak FWHM is 1.1meV and stokes shift is small.
As the electron density become higher, neutral exciton PL and PLE peak become weak
and charged exciton appears and become strong.
This is similar to Fermi Edge Singularity in 2D quantum well optical absorption
spectrum [2].
This effect might be observed in 1D electron-hole system[3], but there are few
experimental reports.
When the density reaches almost 2.5×10 cm
5
1
, Band-to-band transition begins and PL
line shape become broad.
On the other hand the absorption edge become unclear with increased electron plasma
density.
At high density above 2.5×10 cm
5
1
, we observed a large red-shift (2.9meV) and
broadening of PL with increased electron plasma density.
Shrinkage of the optical band-gap with electron plasma due to the many-body Coulomb
interaction is called band-gap renormalization (BGR).
GaAs 量子細線の光分光特性の電子濃度依存性
高品質の N 型ドープ単一 GaAs 細線の PL と PLE で、１次元多体効果を調べた。
試料は MBE と CEO によって作成され、サイズは 14×6nm である。サンプルは cw Ti:Sa
レーザーで励起される。電子濃度は外部電場をかけることで調節する。
我々は、低温における１次元励起子と１次元荷電励起子、そして電子プラズマの発光・吸
収を観測した。
低電子濃度では、励起子からの発光・吸収が主。ピークの形は対称で、ストークスシフト
は小さい。少し電子濃度を上げると、励起子からの発光・吸収は（ブルーシフトしながら）
消え、荷電励起子の発光・吸収が主になる。荷電励起子のピークの形もストークスシフト
は小さい。さらに電子濃度を上げると、荷電励起子からの発光がブロードになり、吸収は
非対称になる。吸収端と発光ピーク間の差が現れる（0.3meV）。高い電子濃度では、BGR
による発光ピークのレッドシフトと、なだらかな吸収端のブルーシフトが観測され、発光
ピークと吸収端の差は大きくなってゆく。
他に書くこと
・ ディテクト、分光器について（方向が違うこと・分解能）
・ exciton の absorption line shape（再度実験して確かめる必要あり）
・ Fermi Edge Singurality について
Electron Density Dependence of Optical Spectroscopy of GaAs Quantum Wire
We
demonstrate
photoluminescence
one-dimensional
(PL)
and
(1D)
many-body
photoluminescence
interaction
excitation
effects
(PLE)
in
in
a
n-type-modulation-doped single GaAs quantum wire of superior quality.
We tune the electron density with application of an external electric field.
At low electron density, emission and absorption of 1D excitons are dominant. As the
electron density become higher, we find charged excitons emission and absorption. And
at high electron density above 2.5×10 cm
5
1
, we find a large red-shift of PL and
blue-shift of PLE with increased electron plasma density.
We find an asymmetrical line shape : a fast rise at the low-energy side and a slow fall at
high energies.
The density of electrons in the wire was changed by applying a negative voltage
between the gate and the contacts.
We observed the appearance of one dimentional excitons and negatively charged
excitons absorption in a GaAs single quantum wire.
We observed PL and PLE experiments in an n-type modulation doped single GaAs
Quantum Wire of superior quality.
We recorded a set of photoluminescence excitation (PLE) and the corresponding PL
spectra for various gate voltages.
An asymmetrical line shape : a fast rise at the low-energy side and a slow fall at high
energies.
Above this density we observe two peaks with asymmetric line shape.
Below this density the exciton peak becomes symmetric and the energy difference
between the two peaks is constant, independent of the density.