Toshiyuki Ihara , Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West
description
Transcript of Toshiyuki Ihara , Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West
Density tuning of one-dimensional Density tuning of one-dimensional electron gaselectron gas
in a doped T-shaped quantum wirein a doped T-shaped quantum wire( ( studied by photoluminescence-studied by photoluminescence-
excitation spectraexcitation spectra ) )Toshiyuki IharaToshiyuki Ihara, Masahiro Yoshita, Hidefumi Akiyama, Masahiro Yoshita, Hidefumi AkiyamaLoren N. Pfeiffer, Ken W. WestLoren N. Pfeiffer, Ken W. West
Institute for Solid State Physics, University of Tokyo, and CREST, JST, JapanInstitute for Solid State Physics, University of Tokyo, and CREST, JST, JapanBell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 0797Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 0797
44
’’07 5/807 5/8 QTuL4QTuL4 @ Q@ QELSELS
OutlineⅠ Introduction / Sample / Optical setup
Ⅱ Results for high-density 1D electron gasⅢ Results for electron-density dependencesⅣ Summary
Introduction : Low-dimensional electron systems in Introduction : Low-dimensional electron systems in semiconductorsemiconductor
VkCk
kk ffEI 1
Vk
Ck
kk ffEA 1
1986 Asada et. al., IEEE J. Quantum Electron.
Sharp density of states (DOS)Quantum (Fermi / Bose) statistics
Many-body effect (Exciton, Trion, FES, BGR)
Interests in Fundamental physics and Applications in Low-dimensional system
Quantum wire Laser diodeM. Okano et al., App. Phys. Lett. 90, 091108 (2007).S. Liu et al., Jpn. J. Appl. Phys. 46, L330 (2007).
Early works of experiments on Low-dimentional electron systemsEarly works of experiments on Low-dimentional electron systems2D electron system
Density-tuning of 2DEG by gate Absorption measurements Interesting physics
1D electron system
’91 J. M. Calleja, SSC
’01 D. Y. Oberli, Physica E
’02 H. Akiyama, SSC
1D FES effect
1D BGR effect
’87 M. S. Skolnick, PRL
’93 K. Kheng, PRL
’99 V. Huard, PRL
’00 R. Kaur, PSS(b) [1]
’02 T. Ogawa, Nonlinear Opt.
Fermi edge singularity (FES)
Trions (Charged excitons)
evolution from trions to FES
calculations (FES theory)
sample growthoptical measurement
High-quality single quantum wire Density-tuning of 1DEG by gate Absorption measurements
< Targets of our investigation >
Experimental Difficulties in
Small number ofexperimental works
[1]
FES
Excitons (X)
Trions (X-)
Band-to-Band
recombination
Ele
ctro
n d
ensi
ty
high
low
T-wire fabricated by Cleaved edge overgrowth T-wire fabricated by Cleaved edge overgrowth methodmethod
< wire size >
14 x 6nm x 4mm (single)
< doping [2] >
①Si modulation doping②gate electrode → tunable density
Epitaxy was done by Dr. L. N. Pfeiffer in Lucent-Bell lab in U.S.
① ② ③ ④
[1] M. Yoshita, H. Akiyama, L. N. Pfeiffer, and K. W. West, Jpn. J. Appl. Phys. 40, L252 (2001).[2] H. Akiyama, L. N. Pfeiffer, A. Pinczuk, K. W. West, and M. Yoshita, Solid State Commun. 122, 169 (2002).
[1]
Optical setupOptical setup
Point 1 keep excitation power stablePoint 2 set excitation and detection perpendicular to each other
PLE measurement on a ground state of a single T-wire
Point 3 set the sample angle tilted and cut laser scattering by iris Point 4 set polarization of excitation and detection perpendicular to each other
PL (photoluminescence)PLE (PL-excitation)
- emission- absorption
We succeeded
Results for high-density 1D electron gasResults for high-density 1D electron gas
5K
We observed PL peak at Band edge and PLE onset at Fermi edge
Exc.
Pex = 40W
Small hole density
Estimation of carrier temperature from PL/PLE Estimation of carrier temperature from PL/PLE ratioratio
We observed PL peak at Band edge and PLE onset at Fermi edge
Estimated temperature : 9.8±0.5K ( kBT
~ 1meV )
Sawicki et al., Phys. Rev. A54, 4837 (1996).
Chatterjee et al., Phys. Rev. Lett. 92, 067402 (2004).
TkA
I
B
exp
We observed PL peak at Band edge and PLE onset at Fermi edge
Estimation of electron density by free-particle model Estimation of electron density by free-particle model calculationcalculation
Estimated density : 6x105 cm-1 ( Ef
~ 5meV )
VkCk
kk ffEI 1
Vk
Ck
kk ffEA 1
Pronounced FES effect was NOT observed
Ef/kBT ~5Estimated temperature : 9.8±0.5K ( kBT
~ 1meV )
Asada et. al., IEEE J. Quantum Electron.
(1986)
0067.0 mme 0105.0 mmh
Temperature dependence of Temperature dependence of PL PL and and PLE PLE at 0.7Vat 0.7V
tem
pera
ture
high
low
We observed Signature of 1D DOS singularity at Band-edge absorption peak
T=5K (Ef/kBT ~ 5 )
PLE onset at Fermi edge (FE)
T=50K (Ef/kBT ~ 1)
sharp PLE peak at Band edge (BE)
Good agreement with calculations.Characteristic of 1D systems.
Gate-voltage dependences at 5KGate-voltage dependences at 5K
Gate
volt
age
high
low
Estimated density : 6x105 cm-1 ( Ef
~ 5meV )
Non-doped limit at Zero density ( Ef
~ 0meV )
Gate-voltage dependences at 5K (0.7 - 0.5 Gate-voltage dependences at 5K (0.7 - 0.5 V)V) Red shifting PLE onset at Fermi
edge
Red shift of Fermi edge Decrease of Electron density
Gate-voltage dependences at 5K (0.4 - 0.35 Gate-voltage dependences at 5K (0.4 - 0.35 V)V)Characteristic double peak
structure
We observed Characteristic double peak PLE structure with Band edge and Fermi edge
Gate-voltage dependences at 5K (0.3 – 0 V)Gate-voltage dependences at 5K (0.3 – 0 V) Crossover to excitonic regime (Vg < 0.2V) from band-to-band recombination regime (Vg > 0.3V) Analogous to the results for 2D electron systems [’99 V. Huard, PRL, '00 R. Kaur, PSS(b), '02 T. Ogawa, Nonlinear Opt. ]
Gate-voltage dependences at 5K (0.3 – 0 V)Gate-voltage dependences at 5K (0.3 – 0 V)
PLE at 0V is consistent with that of non-doped quantum wire [ Itoh et al., APL 83, 2043 (2003). ] 0V corresponds to Limit of non dope (zero density)
Splitting of X should be due toML fluctuations of stem well
Crossover to excitonic regime (Vg < 0.2V) from band-to-band recombination regime (Vg > 0.3V) Analogous to the results for 2D electron systems [’99 V. Huard, PRL, '00 R. Kaur, PSS(b), '02 T. Ogawa, Nonlinear Opt. ]
Comparison whole experimental results with Comparison whole experimental results with calculationscalculations
ne=3x105cm-1 ~ 2.5x105cm-1
Non-degenerated 1D electron gas (Ef/kBT < 2)Double peak induced by 1D DOS
ne < 1.5x105cm-1
Limit of non dope (zero density)
Signature of 1D DOS singularity also appears in the characteristic double peak structure at 0.35-0.4V !!
Ele
ctro
n d
ensi
ty
high
low
Vg = 0.7 - 0.4 V
ne=6x105cm-1 ~ 3x105cm-1
Degenerated 1D electron gas (Ef/kBT > 2)Vg = 0.4 - 0.35
V
Vg < 0.2 V
Differences between 2D and 1D systemsDifferences between 2D and 1D systems2D electron system
Density-tuning of 2DEG by gate PL and PLE measurements Interesting physics
1D electron system’87 M. S. Skolnick, PRL
’93 K. Kheng, PRL
’99 V. Huard, PRL
’00 R. Kaur, PSS(b) [1]
’01 G. Yusa, PRL
strong FES
charged exciton (Trions)
evolution from trions to FES
Trions with Fractional QHE
[1]
FES
Excitons (X)
Trions (X-)
Band-to-Band
recombination
Ele
ctro
n d
ensi
ty
high
low
Signature of 1D DOS singularity
Unique feature of High-quality1D electron systems
Characteristic double peak structure with
band edge and Fermi edge
SummarySummary
Variable-density 1D electron gas was realized
in a T-shaped quantum wire with a gate structure.
PLE measurements on a 1D ground states
were achieved on an isolated single quantum wire.
We observed a signature of 1D DOSrepresented by an absorption peak at the band
edge,which indicates a high uniformity of our sample.
The tunable density range covers from 0 to 6x105cm-1
Future investigation
Remove ML fluctuations in the stem well ( ~ 0.2meV) Measurements at much lower temperature (T < 5K) Measurements under magnetic field (B ~ 10T)
PLE measurement on ground states absorption PLE measurement on ground states absorption peakpeak
The amount of laser scattering is smaller than that of PL
We can set the PLE window for the ground state emission !!
M. S. Skolnick et al., Phys. Rev. Lett. 58, 2130 (1987).M. S. Skolnick et al., Phys. Rev. Lett. 58, 2130 (1987). PL of doped InGaAs quantum wells at various Temperature
Observation of strong FES effects
K. Kheng et al., Phys. Rev. Lett. 71, 1752 (1993).K. Kheng et al., Phys. Rev. Lett. 71, 1752 (1993). Absorption of dilute-doped CdTe quantum wells
under magnetic field
Observation of negatively charged excitons
V. Huard et al., Phys. Rev. Lett. 84, 187 (1999).V. Huard et al., Phys. Rev. Lett. 84, 187 (1999). Absorption of doped CdTe wells at various density
under magnetic field
Observation of crossover from X- to FES
R. Kaur et al., Phys. Status Solidi B 178, 465 (20R. Kaur et al., Phys. Status Solidi B 178, 465 (2000).00).
PLE spectra on doped GaAs quantum wells with a gate
Density-tuning of 2DEG by gate PLE measurements
J. M. Calleja et al., Solid State Commun. 79, 911 (199J. M. Calleja et al., Solid State Commun. 79, 911 (1991).1).
PL and PLE spectra on doped GaAs quantum wires
Investigation of 1D FES effects
D. Y. Oberli et al., Physica E 11, 224 (2001).D. Y. Oberli et al., Physica E 11, 224 (2001). PL and PLE spectra on doped V-groove quantum
wires
FES effect can be strong due to extrinsic origin such as higher subband, hole localization.
H. Akiyama et al., Solid State Commun. 122, 169 (200H. Akiyama et al., Solid State Commun. 122, 169 (2002).2).
PL spectra on single doped T-wire at various density
Investigation of 1D BGR effects
M. Yoshita et al., Jpn. J. Appl. Phys. 40, L252 (20M. Yoshita et al., Jpn. J. Appl. Phys. 40, L252 (2001).01).
Succeeded to improve the uniformity of the second QW (Arm well)
S. Chatterjee et al., Phys. Rev. Lett. 92, 067402 (2004).S. Chatterjee et al., Phys. Rev. Lett. 92, 067402 (2004). time-resolved PL spectra in conjunction with absorption spectra
multi (20) quantum wells non-doped system pulse excitation non-resonant excitation (13.6meV higher energy)
H. Itoh et al., App. Phys. Lett. 83, 2043 (2003).H. Itoh et al., App. Phys. Lett. 83, 2043 (2003).
X
0V is consistent with the results for non-doped quantum wire
Abstract figure 2 : results for the 1D wireAbstract figure 2 : results for the 1D wire
PL and PLE spectra for doped T-wire at 0.7V and 0V
Abstract figure 3 : results for the 2D Arm wellAbstract figure 3 : results for the 2D Arm well
PL and PLE spectra for Arm well at 0.8V and 0.2V
Characterization Characterization ~ ~ PL and PLE spectra PL and PLE spectra overviewoverview
A clear PLE peak of wire ground state
stokes shift < 0.2meV
We assigned the peaks by PL and PLE measurement at various position
Free particle model calculation (C-V Free particle model calculation (C-V expression)expression)
VkCk
kk ffEI 1
Vk
Ck
kk ffEA 1
0067.0 mme
0105.0 mmh
/11 D
''1'0 1 dBffI VC
D
''1'0 1 dBffA VC
D
VC
e
CC m
k
2
22
h
VV m
k
2
22
1/exp1 Tkf BCCCC
1/exp1 Tkf BVVVV
2
2'exp'
B
VC kk
1D DOS, Effective mass approximation, k-conservation
Fermi distribution functions, Carrier densities
Broadening functions
0 1 dfn i
Di VCi ,
Free particle model calculation (e-h expression)Free particle model calculation (e-h expression) VkC
kk
k ffEI 1
Vk
Ck
kk ffEA 1
0067.0 mme
0105.0 mmh
/11 D
'''0 1 dBffI he
D
''11'0 1 dBffA he
D
he
e
ee m
k
2
22
h
hh m
k
2
22
1/exp1 Tkf Beeee
1/exp1 Tkf Bhhhh
2
2'exp'
B
he kk
1D DOS, Effective mass approximation, k-conservation
Fermi distribution functions, Carrier densities
Broadening functions
0 1 dfn i
Di VCi ,
Processing on T-shaped quantum wireProcessing on T-shaped quantum wire