Photoluminescence-excitation spectra on n-type doped quantum wire 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) 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 Dotted line non-interacting free particle Solid line includes many-body effect (Fermi edge singularity) emission 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 Doped multi V-groove wires Calleja et al., Solid State Commun. 79, 911 (1991) Oberli et al., Physica E 11, 224 (2001) Strong FES effect Weak FES effect

Background ～ experiments of doped 1D system ② Doped single T-wire Doped nanotube Akiyama et al., Solid State Commun. 122, 169 (2002) Htoon et al., Phys. Rev. Lett. 93, 027401 (2004) Weak FES effect Strong FES effect What causes strong FES effect ? Where is 1D DOS singularity ?

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

A clear PLE peak of wire ground state was obtained. PL and PLE overview A clear PLE peak of wire ground state was obtained. stokes shift ＜0.2meV 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 ① ② What is the origin of double peak ?

Free particle calculation G = 0.2meV Te = Th = 8K Effective mass 2 band model、 　Fermi distribution of electron gas absorption emission

FES effect is not strong. 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 G = 0.5meV Te = Th BE　：Band Edge　 FE　：Fermi Edge Sharp absorption peak of at 50K corresponds to 1D DOS singularity !! BE

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

＜Further investigation＞ 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　(1×105cm-1 ) ＜Further investigation＞ Study the effect of hole localization on the Fermi edge singularity by Carbon-acceptor doped quantum wire