Browsing by Author "Wu, Yu-Nien"

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Electrically sign-reversible transverse g-factors of holes in droplet epitaxial GaAs/AlGaAs quantum dots under uniaxial stress
(2017-08-23)
Wu, Yu-Nien
;
Wu, Ming-Fan
;
Ou, Ya-Wen
;
Chou, Ying-Lin
;
Cheng, Shun-Jen
We present a theoretical investigation of anisotropic g-factor tensors of single holes confined in droplet epitaxial GaAs/AlGaAs quantum dots under electrical and mechanical controls using the gauge-invariant discretization method within the framework of four-band Luttinger-Kohn (k) over right arrow.(p) over right arrow theory. We reveal an intrinsic obstacle to realize the electrical sign reversal of the hole g-factors, being a key condition required for a full spin control in the scheme of g-tensor modulation, for the quantum dots solely with electrical bias control. Constructively, our studies show that, besides electrical gating, slightly stressing an inherently unstrained droplet epitaxial GaAs/AlGaAs quantum dot can offset the transverse hole g-factor to be nearly zero and make the electrical sign reversal of the hole g-factors feasible.
Optimal electromechanical control of the excitonic fine structures of droplet epitaxial quantum dots
(2018-10-19)
Cheng, Shun-Jen
;
Yang, Yi
;
Wu, Yu-Nien
;
Liao, Yu-Huai
;
Peng, Guan-Hao
The intrinsic fine structure splittings (FSSs) of the exciton states of semiconductor quantum dots (QDs) are known to be the major obstacle for realizing the QD-based entangled photon pair emitters. In this paper, we present a theoretical and computational investigation of the excitonic fine structures of droplet-epitaxial (DE) GaAs/AlGaAs QDs under the electromechanical control of micromachined piezoelectric actuators. From the group theory analysis with numerical confirmation based on the developed exciton theory, we reveal the general principle for the optimal design of micromachined actuators whose application onto an elongated QD can certainly suppress its FSS. We show that the use of two independent tuning stresses is sufficient to achieve the FSS elimination but is not always necessary as widely deemed. The use of a single tuning stress to eliminate the FSS of an elongated QD is possible as long as the crystal structure of the actuator material is in coincidence with that of the QD. As a feasible example, we show that a single symmetric biaxial stress naturally generated from the (001) [Pb(Mg1/3Nb2/3)O-3](0.)(72)-[PbTiO3](0.)(28) (PMN-PT) actuator can be used as a single tuning knob to make the full FSSelimination for elongated DE GaAs QDs.
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