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Toshiyuki Ihara , Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West

’ 07 5/8 QTuL4 @ QELS. Density tuning of one-dimensional electron gas in a doped T-shaped quantum wire ( studied by photoluminescence-excitation spectra ). Toshiyuki Ihara , Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West

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Toshiyuki Ihara , Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West

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  1. ’07 5/8QTuL4@ QELS Density tuning of one-dimensional electron gasin a doped T-shaped quantum wire( studied by photoluminescence-excitation spectra ) Toshiyuki Ihara, Masahiro Yoshita, Hidefumi Akiyama Loren N. Pfeiffer, Ken W. West Institute for Solid State Physics, University of Tokyo, and CREST, JST, Japan Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974 Outline ⅠIntroduction / Sample / Optical setup ⅡResults for high-density 1D electron gas ⅢResults for electron-density dependences ⅣSummary

  2. Introduction : Low-dimensional electron systems in semiconductor 1986 Asada et. al., IEEE J. Quantum Electron. Interests in Fundamental physics and Applications in Low-dimensional system Sharp density of states (DOS) Quantum (Fermi / Bose) statistics Many-body effect (Exciton, Trion, FES, BGR) Quantum wire Laser diode M. Okano et al., App. Phys. Lett. 90, 091108 (2007). S. Liu et al., Jpn. J. Appl. Phys. 46, L330 (2007).

  3. Early works of experiments on Low-dimentional electron systems [1] FES 2D electron system 1D electron system ’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) ’91 J. M. Calleja, SSC ’01 D. Y. Oberli, Physica E ’02 H. Akiyama, SSC 1D FES effect 1D BGR effect Experimental Difficulties in sample growth optical measurement low Excitons (X) Trions (X-) Electron density Small number ofexperimental works high Band-to-Band recombination < Targets of our investigation > • High-quality single quantum wire • Density-tuning of 1DEG by gate • Absorption measurements • Density-tuning of 2DEG by gate • Absorption measurements • Interesting physics

  4. T-wire fabricated by Cleaved edge overgrowth method Epitaxy was done by Dr. L. N. Pfeiffer in Lucent-Bell lab in U.S. ① ② ③ ④ [1] ＜wire size＞ 14 x 6nm x 4mm (single) ＜doping [2]＞ ①Si modulation doping ②gate electrode →tunable density [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).

  5. Optical setup PL (photoluminescence) PLE (PL-excitation) - emission - absorption Point 1 keep excitation power stable Point 2 set excitation and detection perpendicular to each other Point 3set the sample angle tilted and cut laser scattering by iris Point 4set polarization of excitation and detection perpendicular to each other We succeeded PLE measurement on a ground state of a single T-wire

  6. Results for high-density 1D electron gas Exc. 5K Pex = 40mW Small hole density We observed PL peakatBand edge and PLE onsetatFermi edge

  7. Estimation of carrier temperature from PL/PLE ratio Sawicki et al., Phys. Rev. A54, 4837 (1996). Chatterjee et al., Phys. Rev. Lett. 92, 067402 (2004). We observed PL peakatBand edge and PLE onsetatFermi edge Estimated temperature :9.8±0.5K（kBT～ 1meV）

  8. Estimation of electron density by free-particle model calculation Asada et. al., IEEE J. Quantum Electron. (1986) We observed PL peakatBand edge and PLE onsetatFermi edge Pronounced FES effect was NOT observed Estimated temperature :9.8±0.5K（kBT～ 1meV） Ef/kBT ～５ Estimated density :6x105 cm-1（Ef ～ 5meV）

  9. Temperature dependence of ＰＬ and ＰＬＥ at 0.7V T=5K (Ef/kBT ～ ５) high PLE onset at Fermi edge (FE) temperature T=50K (Ef/kBT ～ 1) sharp PLE peak at Band edge (BE) low Good agreement with calculations. Characteristic of 1D systems. We observed Signature of 1D DOS singularityat Band-edge absorption peak

  10. Gate-voltage dependences at 5K Estimated density :6x105 cm-1（Ef ～ 5meV） high Gate voltage low Non-doped limit at Zerodensity（Ef ～ 0meV）

  11. Gate-voltage dependences at 5K (0.7 - 0.5 V) • Red shifting PLE onset at Fermi edge Red shift of Fermi edge Decrease of Electron density

  12. Gate-voltage dependences at 5K (0.4 - 0.35 V) • Characteristic double peak structure We observed Characteristic double peak PLE structure with Band edge and Fermi edge

  13. 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. ]

  14. 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. ] • Splitting of X should be due toML fluctuations of stem well PLE at 0V is consistent with that of non-doped quantum wire [ Itoh et al., APL 83, 2043 (2003). ] 0V corresponds toLimit of non dope (zero density)

  15. Comparison whole experimental results with calculations Vg = 0.7 - 0.4 V ne=6x105cm-1～ 3x105cm-1Degenerated 1D electron gas(Ef/kBT > 2) high Vg = 0.4 - 0.35 V ne=3x105cm-1～ 2.5x105cm-1Non-degenerated 1D electron gas(Ef/kBT < 2) Electron density Double peak induced by 1D DOS low Vg < 0.2 V 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 !!

  16. Differences between 2D and 1D systems [1] FES 2D electron system 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 Characteristic double peak structure with band edge and Fermi edge low Excitons (X) Trions (X-) Electron density high Band-to-Band recombination • Signature of 1D DOS singularity • Density-tuning of 2DEG by gate • PL and PLE measurements • Interesting physics Unique feature of High-quality1D electron systems

  17. Summary Variable-density 1D electron gas was realizedin 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 (g ～0.2meV) • Measurements at much lower temperature (T＜5K) • Measurements under magnetic field (B～10T)

  18. PLE measurement on ground states absorption peak The amount of laser scattering is smaller than that of PL • We can set the PLE window for the ground state emission !!

  19. 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

  20. K. Kheng et al., Phys. Rev. Lett. 71, 1752 (1993). • Absorption of dilute-doped CdTe quantum wellsunder magnetic field • Observation of negatively charged excitons

  21. V. Huard et al., Phys. Rev. Lett. 84, 187 (1999). • Absorption of doped CdTe wells at various densityunder magnetic field • Observation of crossover from X- to FES

  22. R. Kaur et al., Phys. Status Solidi B 178, 465 (2000). • PLE spectra on doped GaAs quantum wells with a gate • Density-tuning of 2DEG by gate • PLE measurements

  23. J. M. Calleja et al., Solid State Commun. 79, 911 (1991). • PL and PLE spectra on doped GaAs quantum wires • Investigation of 1D FES effects

  24. 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.

  25. H. Akiyama et al., Solid State Commun. 122, 169 (2002). • PL spectra on single doped T-wire at various density • Investigation of 1D BGR effects

  26. M. Yoshita et al., Jpn. J. Appl. Phys. 40, L252 (2001). • Succeeded to improve the uniformity of the second QW (Arm well)

  27. 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)

  28. H. Itoh et al., App. Phys. Lett. 83, 2043 (2003). X • 0V is consistent with the results for non-doped quantum wire

  29. Abstract figure 2 : results for the 1D wire • PL and PLE spectra for doped T-wire at 0.7V and 0V

  30. Abstract figure 3 : results for the 2D Arm well • PL and PLE spectra for Arm well at 0.8V and 0.2V

  31. Characterization ～ PL and PLE spectra overview • A clear PLE peak of wire ground state stokes shift ＜0.2meV We assigned the peaks by PL and PLE measurement at various position

  32. Free particle model calculation (C-V expression) • 1D DOS, Effective mass approximation, k-conservation • Fermi distribution functions, Carrier densities • Broadening functions

  33. Free particle model calculation (e-h expression) • 1D DOS, Effective mass approximation, k-conservation • Fermi distribution functions, Carrier densities • Broadening functions

  34. Processing on T-shaped quantum wire

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