Masahiro Yoshita

One-dimensional continuum and exciton states in quantum wires

High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth with molecular-beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Characterization by micro-photoluminescence (PL) and PL excitation (PLE) spectroscopy at 5 K reveals high uniformity, a sharp spectral width, and a small Stokes shift of one-dimensional (1D) excitons. The PLE spectrum for 1D states shows a large peak of ground-state excitons and a small absorption band ascribed to 1D continuum states with an onset at 11 meV above the exciton peak.

Imaging of emission patterns in a T-shaped quantum wire laser

Spatially and spectrally resolved microscopic images of spontaneous and stimulated emissions are imaged at the mirror facets of a GaAs T-shaped quantum wire laser with high uniformity. Laser emission from the one-dimensional ground state reveals a circular image located at the core of a T-shaped optical waveguide but significantly smaller in area than the low power spontaneous emission from the same waveguide. These images unambiguously allow assignment of all spontaneous and laser emissions to the wire ground state and respective intersecting wells in the structure.

Temperature-dependent current injection and lasing in T-shaped quantum-wire laser diodes with perpendicular p- and n-doping layers

The authors measured the temperature dependence of the lasing properties of current-injection T-shaped GaAs∕AlGaAs quantum-wire (T-wire) lasers with perpendicular p- and n-doping layers. The T-wire lasers with high-reflectivity coatings on both cleaved facets achieved continuous-wave single-mode operation between 5 and 110K. The lowest threshold current was 2.1mA at 100K. The temperature dependences of differential quantum efficiency and threshold current were attributed mainly to that of current-injection efficiency.

One-dimensional excitonic states and lasing in highly uniform quantum wires formed by cleaved-edge overgrowth with growth-interrupt annealing

High quality T-shaped quantum wire lasers are fabricated by cleaved-edge overgrowth with molecular beam epitaxy on an interface improved by a growth-interrupt high temperature annealing. Microphotoluminescence and photoluminescence (PL) excitation spectroscopy at low temperatures reveals the formation of quantum wires with unprecedentedly high quality, and intrinsic structures of one-dimensional (1D) free excitons, exciton excited states, and 1D continuum states. At high pumping levels, the PL evolves from showing a sharp free exciton peak via exhibiting a biexciton peak to a Coulomb correlated electron–hole plasma PL band. Lasing has been achieved with a low lasing threshold, and its emission patterns are measured in imaging experiments. The lasing energy is in the plasma PL band and is about 5xa0meV below the free exciton level. The observed shift excludes the possibility of free excitons in the lasing, and suggests a contribution from the electron–hole plasma. Single T-wire samples such as a single-quantum-wire laser and a field-effect-transistor-type doped single quantum wire are fabricated and studied optically.

Quantum wire lasers with high uniformity formed by cleaved-edge overgrowth with growth-interrupt anneal

Abstract High-quality T-shaped quantum wire lasers are fabricated by cleaved-edge overgrowth with the molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Micro-photoluminescence (PL) and PL excitation spectroscopy reveals unprecedented high quality of the wires, and structures of one-dimensional (1D) free excitons and 1D continuum states. At high pumping levels, PL evolves from a sharp free exciton peak via a biexciton peak to a red-shifted broad band. Lasing has been achieved with low lasing threshold. The lasing energy is on the red-shifted broad band and is about 5xa0meV below the free exciton. The observed shift excludes free excitons in lasing, and suggests contribution of highly Coulomb-correlated electron–hole plasma.