Transcript et al.
05.12.16 seminar＠ISSP with Kono group Photoluminescence-excitation spectra on n-type doped quantum wire ISSP Akiyama group D1 Toshiyuki Ihara Introduction ～ One dimensional system Inverse-square-root divergence Density of state (DOS) D (E) 1/ E 1D Interesting phenomena appear!! ・Large exciton binding energy. ・Strong absorption of exciton groundstate. ・High speed optical modulation device. ・High performance laser device. Background ～ calculation for doped 1D system ＜Theoretical calculation by Rodriguez et. al.＞ Band bottom Fermi edge absorption emission Dotted line non-interacting free particle Solid line includes many-body effect (Fermi edge singularity) Rodriguez et al., Phys. Rev. B 47, 1506 (1993) “1D DOS singularity” and/or “Fermi edge singularity” would appear. Background ～ experiments of doped 1D system ① Doped multi well-wires Calleja et al., Solid State Commun. 79, 911 (1991) Strong FES effect Doped multi V-groove wires Oberli et al., Physica E 11, 224 (2001) Weak FES effect Background ～ experiments of doped 1D system ② Doped single T-wire Akiyama et al., Solid State Commun. 122, 169 (2002) Doped nanotube Htoon et al., Phys. Rev. Lett. 93, 027401 (2004) Weak FES effect What causes strong FES effect ? Where is 1D DOS Strong FES effect Motivation ～ optical absorption of doped quantum wire For the observation of 1D density of state … ・High-quality ・1D limit ・direct gap structure Our T-shaped wire meet these conditions !! Furthermore, in order to obtain absorption spectra … We developed “High resoluted photoluminescence-excitation (PLE) method” PLE spectra of ground state of single quantum wire are possible to obtain !! Sample structure ＜fabrication＞ MBE with cleaved edge overgrowth method ＜size of wire＞ 14 x 6nm x 4mm(single) ＜doping＞ ①Si modulation doping ②FET gate structure →tunable electron density ＜measurement＞ Polarization selected micro-PL & PLE spectra PL and PLE overview stokes shift ＜0.2meV A clear PLE peak of wire ground state was obtained. How the “wire” peak changes with increasing electron density !? Results for 1D system ※hole density is small Metal-insulator crossover of 1D doped system was observed for the first time. ＜interesting results＞ ①double peak structure at the metal-insulator crossover region. ②remarkable quenching of exciton peak What is the origin of double ① ② = 0.2meV Te = Th = 8K Free particle calculation Effective mass 2 band model、 Fermi distribution of electron gas e h (1 me / mh ) e absorption A D1j D 1 f e e L E g d emission I D1j D f e e f h h L E g d D ( ) 1 / 1D j ne 1 2me 2 1 e f e e d e Comparison good agreement for PLE at high electron density!! Double peak structure ① corresponds to “1D DOS singularity” and “Fermi edge”. ① ② FES effect is not strong. High density and High temperature Calculation parameter = 0.5meV Te = Th BE ：Band Edge FE ：Fermi Edge Sharp absorption peak of BE at 50K corresponds to 1D DOS singularity !! Results for 2D system Same results as other groups ・Finkelstein et al., Phys. Rev. Lett. 74, 976 (1995) ・Huard et al., Phys. Rev. Lett. 84, 187 (1999) ・Yusa et al., Phys. Rev. B 62, 15390 (2000) ・Kaur et al., Phys. Status Solidi B 178, 465 (2000) ・Cox et al., Phys. Rev. B 69, 235303 (2004) Band edge absorption is not sharp peak but step-function onset Conclusion We measured PLE spectra at low temperature on an n-type doped single quantum wire with a gate to tune electron densities. ①A double peak structure corresponding 1D DOS singularity and Fermi edge appeared. ②exciton peak quenches at low density (1×105cm1 ) ＜Further investigation＞ Study the effect of hole localization on the Fermi edge singularity by Carbon-acceptor doped quantum wire