Browsing by Author "Mano, Takaaki"

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Geometrical impact on the optical polarization of droplet epitaxial quantum dots
(2012-09-17)
Liao, Yu-Huai
;
Liao, Chien-Chih
;
Ku, Chih-Hao
;
Chang, Yu-Chen
;
Cheng, Shun-Jen
We report on experimental and theoretical investigations of the optical anisotropy of GaAs/AlGaAs quantum dots grown by droplet epitaxy. With in situ annealing in the growth, the shape of quantum dots is systematically controlled from a tall and laterally symmetric shape to a flat and laterally elongated one. Photoluminescence spectroscopy demonstrates an uncommon observation: the more elongated the quantum dots, the lower the degree of linear polarization. Theoretical analysis based on a four-band k center dot p theory reveals a substantial impact of vertical confinement on the valence heavy-hole and light-hole mixing, which leads to the enhancement of polarization anisotropy for taller quantum dots. The influence of Coulomb interactions on polarization anisotropy is studied by using the partial configuration interaction method, and is shown to reduce the polarization anisotropy through the mixing of single-particle configurations with different symmetries.
Size-dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charge on spectral diffusion
(2015-08-10)
Ha, Neul
;
Mano, Takaaki
;
Chou, Ying-Lin
;
Wu, Yu-Nien
;
Cheng, Shun-Jen
Making use of droplet epitaxy, we systematically controlled the height of self-assembled GaAs quantum dots by more than one order of magnitude. The photoluminescence spectra of single quantum dots revealed the strong dependence of the spectral linewidth on the dot height. Tall dots with a height of similar to 30 nm showed broad spectral peaks with an average width as large as similar to 5 meV, but shallow dots with a height of similar to 2 nm showed resolution-limited spectral lines (<= 120 mu eV). The measured height dependence of the linewidths is in good agreement with Stark coefficients calculated for the experimental shape variation. We attribute the microscopic source of fluctuating electric fields to the random motion of surface charges at the vacuum-semiconductor interface. Our results offer guidelines for creating frequency-locked photon sources, which will serve as key devices for long-distance quantum key distribution.
Wavelength extension beyond 1.5 mu m in symmetric InAs quantum dots grown on InP(111)A using droplet epitaxy
(2016-10)
Ha, Neul
;
Mano, Takaaki
;
Wu, Yu-Nien
;
Ou, Ya-Wen
;
Cheng, Shun-Jen
By using a C-3v symmetric (111) surface as a growth substrate, we can achieve high structural symmetry in self-assembled quantum dots, which are suitable for use as quantum-entangled-photon emitters. Here, we report on the wavelength controllability of InAs dots on InP(111)A, which we realized by tuning the ternary alloy composition of In(Al, Ga) As barriers that were lattice-matched to InP. We changed the peak emission wavelength systematically from 1.3 to 1.7 mu m by barrier band gap tuning. The observed spectral shift agreed with the result of numerical simulations that assumed a measured shape distribution independent of the barrier choice. (C) 2016 The Japan Society of Applied Physics