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2004 Fall MRS meeting in Boston (2004.11.30 B3.1) T-shaped quantum-wire laser M. Yoshita, Y. Hayamizu, Y. Takahashi, H. Itoh, T. Ihara, and H. Akiyama Institute for Solid State Physics, Univ. of Tokyo and CREST, JST L. N. Pfeiffer, K. W. West, and Ibo Matthews Bell Laboratories, Lucent Technologies 1. Formation of high-quality GaAs T-shaped quantum wires Cleaved-edge overgrowth with MBE, AFM, PL, PLE 2. Single-wire laser PL scan, Lasing, PL, Absorption/Gain via Cassidy’s method, Transmission 3. Observation of RT 1D exciton absorption in 20-wire laser 4. Optical response of n-doped single-wire FET device T-shaped Quantum Wire (T-wire) Cleaved-edge overgrowth with MBE by L. N. Pfeiffer et al., APL 56, 1679 (1990). [110] [001] GaAs substrate (001) MBE Growth 600oC Cleave in situ o (490 C) (110) MBE Growth 490oC Nomarski Microscope Images of Cleaved-EdgeOvergrowth Surfaces Good Poor “Hackling” Bad High Quality T-wire ??? 490C Growth Atomically flat interfaces (By Yoshita et al. JJAP 2001) High Quality T-wire !? 490C Growth 510-600C Anneal Atomically flat interfaces (By Yoshita et al. JJAP 2001) High Quality T-wire !!? 490C Growth 510-600C Anneal Atomically flat interfaces (By Yoshita et al. JJAP 2001) High Quality T-wire !!!!! 490C Growth 510-600C Anneal Atomically flat interfaces (By Yoshita et al. JJAP 2001) 20-wire laser sample 14nm x 6nm 1st growth 600C 2nd growth 490C (arm well) 600C 10min anneal 490C (cover layers) Laser bars 500mm uncoated cavity PL and PLE spectra Sharp PL width Small Stokes shift 1D free exciton 1D continuum states T-wire stem well arm well (Akiyama et al. APL 2003) E-field E-field // to wire _I to wire // to arm well Single quantum wire laser Probability of Photon Cavity length 500 mm G=5x10-4 Probability of Electron Scanning micro-PL spectra T-wire stem well scan T-wire stem well T=5K Continuous PL peak over 20 mm PL width < 1.3 meV 500mm gold-coated cavity Lasing in a single quantum wire Threshold 5mW (Hayamizu et al, APL 2002) Excitation power dependence of PL M. Yoshita, et al. n1D = 1.2 x 106 cm-1 (rs = 0.65 aB) aB ~13nm Density Electron-hole Plasma n1D = 1.2 x 105 cm-1 (rs = 6.6 aB) Biexciton+Exciton EB =2.8meV n1D = 3.6 x 103 cm-1 (rs = 220 aB) Free Exciton n1D ~ 102 cm-1 Absorption/gain measurement based on Hakki-Paoli-Cassidy’s analysis of Fabry-Perot-laser emission below threshold A (1 R) 2 e l I (E) (1 R e l ) 2 4R e l sin 2 θ 1 1 p 1 ln l R p 1 I sum /FSR p I min :Absorption coeff. R :Reflectivity n l E c D. T. Cassidy JAP. 56 3096 (1984) Free Spectral Range B. W. Hakki and T. L. Paoli JAP. 46 1299 (1974) Absorption Spectrum by Cassidy method Single wire laser, uncoated cavity mirrors Excitation Light :cw TiS laser at 1.631eV Spectrometer with spectral resolution of 0.15 meV Cassidy’s Method Point Waveguide Emission Polarization parallel to Arm well Measurement of absorption/gain spectrum Excitation Light :cw TiS laser at 1.631eV Spectrometer with spectral resolution of 0.15 meV Cassidy’s Method Spontaneous emission Stripe shape Waveguide Emission 8.3mW Polarization parallel to Arm well Absorption/gain spectrum (High excitation power) Absorption Electron-Hole Plasma Gain EBE EFE 8.3mW Hayamizu et al. Electron-Hole Plasma 1. Exciton peak and continuum onset decay without shift. 2. Gap between exciton and continuum is gradually filled. 3. Exciton changes to Fermi edge Exciton Hayamizu et al. Transmission measurement of a single quantum wire ~mm ~nm Transmittance for single Coupling efficiency = 20% Takahashi et al. unpublished Absorption for single Takahashi et al. unpublished Absorption for 20 Y. Takahashi et al. Absorption at 300 K Room-Temperature 1D Exciton Absorption! Y. Takahashi et al. 1D electron density 14nmx6nm Doped Single Wire FET device with tunable 1D electron density e he T. Ihara et al. eh Quantum-Wire Devices Summary 1. GaAs T-shaped quantum wires (T-wires) are formed by cleavededge overgrowth with MBE. 2. Growth-interrupt anneals dramatically improve T-wire quality. 3. AFM : No atomic steps over 100mm. 4. PL : Sharp PL width (~1meV) improved by a factor of 10. 5. PLE : Observation of 1D free exciton, & 1D continuum states 6. Single wire lasing : The world thinnest laser (14nm x 6nm), 5mW threshold optical pumping power at 5K. 7. Gain/absorption measurement by Hakki-Paoli-Cassidy’s method. 8. Strong photo-absorption by a single wire 84/cm (98.5% absorption / 500mm) at exciton peak at 5K 9. Room-temperature exciton absorption observed in 20-wire laser. 10. Single-wire FET: carrier-sensitive optical responses. ここまで。25分のトーク。 (001) and (110) surfaces of GaAs (001) [001] (110) [110] [110] [001] Growth rate of GaAs in MBE Substrate rotation >>> uniform Ga limited growth under As4 overpressure Interface control by growth-interruption annealing o High Quality T-wire 490 C Growth o 600 C Anneal arm well 6nm Atomically flat stem well 14nm interfaces (by M. Yoshita et al. JJAP 2001) (By Yoshita et al. APL 2002) Single wire laser with 500mm gold-coated cavity Absorption at higher temperatures by Cassidy Hayamizu et al. unpublished Absorption coefficients Experiment for gain Evolution of continuum Takahashi et al. unpublished Lasing & many-body effects in quantum wires E. Kapon et al. (PRL’89) W. Wegscheider et al. (PRL’93) R. Ambigapathy et al. (PRL’97) L. Sirigu et al. (PRB’00) J. Rubio et al. (SSC’01) A. Crottini et al. (SSC’02) T. Guillet et al. (PRB’03) H. Akiyama et al. (PRB’03) Lasing in excited-states of V-wires Lasing in the ground-state of T-wires, no energy shift, excitonic lasing PL without BGR, strong excitonic effect in V-wires Lasing due to localized excitons in V-wires Lasing observed with e–h plasma emission in T-wires PL from exciton molecules (bi-excitons) in V-wires PL, Mott transition form excitons to a plasma in V-wires Lasing due to e–h plasma, no exciton lasing in T-wires Theories F. Rossi and E. Molinari (PRL’96) F. Tassone, C. Piermarocchi, et al. (PRL’99,SSC’99) S. Das Sarma and D. W. Wang (PRL’00,PRB’01) “1D exciton Mott transition” Physical picture of 1D exciton–plasma transition the exciton Mott transition Increase of e–h pair density causes ・ reduction of exciton binding energy ・ red shift of the band edge (band-gap renormalization (BGR)) eg. D. W. Wang and S. Das Sarma, PRB 64, 195313 (2001). Our PL results show no energy shift of the exciton band edge plasma low-energy edges appear at the bi-exciton energy positions, and show BGR no connection, but coexistence of two band edges band edge exciton level no level-crossing between the band edges and the exciton level Exciton band edge & plasma band edge (T=30K) ▼ plasma band edge (low energy edge of plasma PL) starts at biexciton energy and shows red shift. ▼ exciton band edge, (onset of continuum states) exciton ground and excited states show no shift. Electron plasma and minority hole eeeeheeeee e he X- Charged Exciton X Exciton eh Theory 1D exciton and continuum states