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 and K. W. West Bell Laboratories, Lucent Technologies JSPS-NUS, Japan-Singapore symposium ( ) 1. Formation of high-quality GaAs T-shaped quantum wires Cleaved-edge overgrowth with MBE, AFM, PL, PLE 2. Single-T-wire laser PL scan, Lasing, Absorption/Gain 3. Single-T-wire FET PL, PLE T-shaped Quantum Wire (T-wire) Cleaved-edge overgrowth with MBE In situ Cleave (001) MBE Growth (110) MBE Growth [110] [001] GaAs substrate 600 o C490 o C by L. N. Pfeiffer et al., APL 56, 1679 (1990). 490C Growth (By Yoshita et al. JJAP 2001) Atomically flat interfaces High Quality T-wire ??? 490C Growth (By Yoshita et al. JJAP 2001) Atomically flat interfaces High Quality C Anneal T-wire !? 490C Growth (By Yoshita et al. JJAP 2001) Atomically flat interfaces High Quality C Anneal T-wire !!? 490C Growth (By Yoshita et al. JJAP 2001) Atomically flat interfaces High Quality C Anneal T-wire !!!!! (001) and (110) surfaces of GaAs (001) (110) [001] [110] [001] (Akiyama et al. APL 2003) PL and PLE spectra 1D free exciton small Stokes shift 1D continuum states arm well stem well T-wire E-field // to wire _ to wire // to arm well I E-field Cavity length 500 m Probability of Photon Probability of Electron Single quantum wire laser =5x10 -4 Scanning micro-PL spectra Continuous PL peak over 20 m PL width < 1.3 meV scan T=5K T-wire stem well 500 m gold-coated cavity Threshold 5mW (Hayamizu et al, APL 2002) Lasing in a single quantum wire Single wire laser with 500 m gold-coated cavity Transmittance for single Takahashi et al. unpublished Coupling efficiency = 20% Absorption for single Takahashi et al. unpublished Absorption at 300 K Takahashi et al. unpublished Experiment for gain Evolution of continuum Takahashi et al. unpublished 1D electron-gas density 1D electron-gas-density control in a FET-type single quantum wire 14nmx6nm ehe eh E f =6meV E f = 2meV m e =0.067 m 0 m h =0.105 m 0 E b =2meV Optically pumped lasers Current injection lasers Threshold current? High differential gain? Fast modulation? Switch & Modulator Large non-linearity? Quantum-Wire Devices Summary Thanks ! 1.GaAs T-shaped quantum wires (T-wires) are formed by cleaved- edge overgrowth with MBE. 2.Growth-interrupt anneals dramatically improve T-wire quality. 3.AFM : No atomic steps over 100 m. 4.PL : Sharp PL width (~1meV) improved by a factor of PLE : Observation of 1D free exciton, & 1D continuum states 6.Single wire lasing : The world thinnest laser (14nm x 6nm), 5-60K, 5mW threshold optical pumping power at 5K. 7.Strong absorption by a single wire 84/cm (98.5% absorption / 500 m) at exciton peak at 5K 8.Room-temperature exciton absorption observed in 20-wire laser. 9.Single-wire FET is formed and optically studied. 10.In progress : physics, current injection, amplification, modulation. Experiment How to derive Absorption for 20 Absorption coefficients 1.Exciton peak and continuum onset decay without shift. 2.Gap between exciton and continuum is gradually filled. 3.Exciton changes to Fermi edge Electron-Hole Plasma Exciton Hayamizu et al. unpublished Absorption at higher temperatures by Cassidy Hayamizu et al. unpublished B. W. Hakki and T. L. Paoli JAP (1974) Reflectivity Absorption coeff. D. T. Cassidy JAP (1984) Absorption/gain measurement based on Cassidys analysis of Fabry-Perot-laser emission below threshold Free Spectral Range 490 o C Growth High Quality T-wire Interface control by growth-interruption annealing (by M. Yoshita et al. JJAP 2001) Atomically flat interfaces 600 o C Anneal arm well 6nm stem well 14nm (By Yoshita et al. APL 2002) X - Charged Exciton X Exciton Electron plasma and minority hole eh ehe eheeeeeeee