Near band edge polarization dependence as a probe of structural symmetry in GaAs/AlGaAs quantum dot structures

Tanaka, T.; Singh, Jasprit; Arakawa, Yasuhiko; Bhattacharya, P.

doi:10.1063/1.108569

Cited by 33 publications

(21 citation statements)

References 13 publications

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“…Whereas in 0D QDs k i is replaced by the operator −i ∂ ∂r i (i = x, y, z) as a result of space confinement, the ground state has an effective finite wavevector which leads to finite R and S and thus δV HL = 0. Such 3D quantum confinement was previously considered as the only mechanism leading to HH-LH mixing in unstrained QDs 5,14,[20][21][22] . For flat GaAs QDs [where a z (height) ≪ L(wide)], 3D confinement within the Luttinger-Kohn Hamiltonian gives rise to λ LH ≃ 0.53a z /L 5 and λ 2 LH = 0.2%, a much smaller value than our determined 3.5%, for a disk-shaped dot with a z = 2 nm, L = 25 nm, as shown in Fig.…”

Section: Direct Hh-lh Coupling Effectsmentioning

confidence: 99%

“…The most popular theoretical approach used in nanostructures is to fold the Luttinger-Kohn k · p or PikusBir strained Hamiltonian of bulk zinc-blende (ZB) semiconductors down to an effective 2 × 2 HH Hamiltonian and taking the admixture of neighboring bands such as LH band into account perturbatively [5][6][7][8][9]18 . In the early days of nanostructures research, the HH-LH mixing was depicted as a result of spatial quantum confinement 5,14,[20][21][22][23][24] , which leads to finite off-diagonal matrix elements within the Luttinger-Kohn k · p Hamiltonian. However, δV HL , and thus HH-LH mixing, was later recognized to be zero by the symmetry in symmetric self-assembled QDs which were assumed (incorrectly) to have the D 2d point group [11][12][13]19 .…”

Section: Introductionmentioning

confidence: 99%

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Supercoupling between heavy-hole and light-hole states in nanostructures

2015

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The heavy-hole (HH) and light-hole (LH) components of the valence states in 3D bulk semiconductors can mix quantum mechanically as the dimensionality is reduced in forming 2D, 1D nanostructures and 0D quantum dots (QDs). This coupling controls the tuning of the excitonic fine structure splitting, provides an efficient channel for the spin coherence, and leads to polarization anisotropy of light emission, central to several quantum information schemes. Current understanding is that the mixing scales with the square of δV HL /∆ HL , where δV HL and ∆ HL are the coupling matrix elements of the crystal potential and the energy separation between the primary HH0 and LH0 states, respectively. We discuss two classes of HH-LH coupling mechanisms.First, coupling factors occurring through the numerator δV HL , referred to as "direct coupling", including the well-known (1) quantum confinement, (2) built-in strain, and (3) shape elongation, as well as three additional direct coupling mechanisms discussed here: (4) the intrinsic C 2v crystal field effect, (5) the local symmetry of the interface, and (6) the alloy disorder. We quantify these 6 direct HH-LH coupling effects by performing atomistic pseudopotential calculations on a range of strained and unstrained QDs of different morphologies. We find that in unstrained self-assembled QDs such as GaAs/AlGaAs effects (1)-(6) contribute 0%, 0%, 0%, 0%, 40%, and 60%, respectively, whereas in strained self-assembled QDs such as InGaAs/GaAs they contribute 0%, 0%, 78%, 0%, 8%, and 14%, respectively, to the direct HH-LH coupling δV HL . These relative contributions to direct HH-LH coupling differ significantly from what was previously believed.Second, we discover an unexpected HH-LH coupling that effectively reduces the denominator ∆ HL by the presence of a dense ladder of intermediate states between the HH0 and LH0 states (analogous to super-exchange in magnetism). Supercoupling amplifies and propagates the HH-LH interaction and is the dominant source of HH-LH mixing in strained nanostructures where ∆ HL is fairly large, so by the direct coupling mechanism alone δV HL /∆ HL would be expected to be rather small. Supercoupling explains a number of outstanding puzzles including the surprising fact that in strained (InAs/GaAs) QDs the mixing is very strong despite the fact that ∆ HL is large, and offers a new way to manipulate HH-LH mixing and hence associated properties in nanostructures.

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Section: Direct Hh-lh Coupling Effectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Supercoupling between heavy-hole and light-hole states in nanostructures

2015

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“…The relative intensities of the different lines [e.g., the difference in intensities between the ͑x 0 x 0 ͒ and ͑ y 0 y 0 ͒ polarizations for E 3 , etc.] likely arises from mixing of the heavy and light holes due to the QD potential [11]. Inversion asymmetries in the QD potential and/or local uniaxial strain coupled with spin-orbit interaction may lead to a lifting of the spin degeneracy in the electron and hole single particle states [12].…”

Section: Form Approved Omb No 0704-0188mentioning

confidence: 99%

Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

et al. 1996

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We report a photoluminescence study of excitons localized by interface fluctuations in a narrow GaAs͞AlGaAs quantum well. This type of structure provides a valuable system for the optical study of quantum dots. By reducing the area of the sample studied down to the optical near-field regime, only a few dots are probed. With resonant excitation we measure the excited-state spectra of single quantum dots. Many of the spectral lines are linearly polarized with a fine structure splitting of 20 -50 meV. These optical properties are consistent with the characteristic asymmetry of the interface fluctuations. PACS numbers: 78.55.Cr, 71.35.Cc In this Letter we describe the polarization dependence of the optical spectra of single naturally formed GaAs quantum dots. Most previous optical studies of quantum dots (QDs) have probed large ensembles which have led to inhomogeneous broadening of the spectral features. However, recently several groups have shown that it is possible to study single QDs with photoluminescence (PL) either by reducing the size of the sample, [1] by cathodoluminescence [2,3], or by reducing the size of the laser spot on the sample through microscopic [4,5] or optical near-field techniques [6]. Here we use a similar technique whereby we combine high spatial and spectral resolution optics with excitation spectroscopy to study in detail the spectrum of a single QD [7]. With improved resolution we are able to resolve the spectral lines and to study the polarization dependence of the PL spectrum of an individual QD. We often find that the PL is linearly polarized along the (110) crystal axes and observe a fine structure splitting in each of the spectral lines. These results are analogous to the early days of atomic spectroscopy as improvements in techniques allowed the observation of fine structure splittings in the optical spectra. However, the physical phenomena responsible for the effects presented here are unique to the quantized condensed matter system.The QDs we have studied were formed naturally by interface steps in narrow quantum wells [4][5][6][7]. Specifically, the electrons and holes become localized into QDs in regions of the quantum well that are a monolayer wider than the surrounding region and, therefore, have a slightly smaller confinement energy. These well width fluctuations arise from monolayer-high islands at the interfaces which are randomly formed on the growth-interrupted surface by the migration of the cations to step edges. By interrupting the growth these islands can grow to diameters larger than the exciton Bohr diameter (20 nm). A scanning tunneling microscope image of a growth-interrupted GaAs surface grown under similar conditions as our quantum dot sample is shown in Fig. 1. Large monolayer-high islands of varying lateral sizes are evident, and the islands tend to be elongated along the [110] crystal axis. Thus we intuitively expect that the optical properties associated with the localized excitons will reflect this characteristic interface structure. In fact, as we will...

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“…The excitonic fine structure and the polarization of the optical transitions have profound relations with the underlying symmetries of the nanostructures. However, despite the usual interpretation of polarization anisotropy in terms of valence-band mixing [12], and a recent demonstration of the vanishing fine-structure splitting in QDs [13,14], a general understanding of the relation between symmetry and the complex polarization spectra of excitons and excitonic complexes is still lacking.…”

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confidence: 99%

Symmetries and the Polarized Optical Spectra of Exciton Complexes in Quantum Dots

et al. 2011

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A systematic and simple theoretical approach is proposed to analyze true degeneracies and polarized decay patterns of exciton complexes in semiconductor quantum dots. The results provide reliable spectral signatures for efficient symmetry characterization, and predict original features for low C(2 nu) and high C(3 nu) symmetries. Excellent agreement with single quantum dot spectroscopy of real pyramidal InGaAs/AlGaAs quantum dots grown along [111] is demonstrated. The high sensitivity of biexciton quantum states to exact high symmetry can be turned into an efficient uninvasive postgrowth selection procedure for quantum entanglement applications

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Near band edge polarization dependence as a probe of structural symmetry in GaAs/AlGaAs quantum dot structures

Cited by 33 publications

References 13 publications

Supercoupling between heavy-hole and light-hole states in nanostructures

Supercoupling between heavy-hole and light-hole states in nanostructures

Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

Symmetries and the Polarized Optical Spectra of Exciton Complexes in Quantum Dots

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