Effective-mass theory for InAs/GaAs strained coupled quantum dots

Li, Shu-Shen; Xia, Jian‐Bai; Yuan, Zhiliang; Xu, Zhongying; Ge, Weikun; Wang, Xiangrong; Wang, Yi; Wang, Jiannong; Chang, L.L.

doi:10.1103/physrevb.54.11575

Cited by 162 publications

(78 citation statements)

References 28 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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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] SAQDs are the result of a transition from 2D growth to 3D growth in strained epitaxial films such as Si x Ge 1Àx =Si and In x Ga 1Àx As/GaAs: This process is known as Stranski-Krastanow growth or VolmerWebber growth. 3,[15][16][17] In applications, order of SAQDs is a key factor.…”

Section: Introductionmentioning

confidence: 99%

Predicting and Understanding Order of Heteroepitaxial Quantum Dots

Friedman

2007

Journal of Elec Materi

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Heteroepitaxial self-assembled quantum dots (SAQDs) will allow breakthroughs in electronics and optoelectronics. SAQDs are a result of Stranski-Krastanow growth, whereby a growing planar film becomes unstable after an initial wetting layer is formed. Common systems are Ge x Si 1Àx =Si and In x Ga 1Àx As/GaAs: For applications, SAQD arrays need to be ordered. The roles of crystal anisotropy, random initial conditions and thermal fluctuations in influencing SAQD order during early stages of SAQD formation are studied through a simple stochastic model of surface diffusion. Surface diffusion is analyzed through a linear and perturbatively non-linear analysis. The role of crystal anisotropy in enhancing SAQD order is elucidated. It is also found that SAQD order is enhanced when the deposited film is allowed to evolve at heights near the critical wetting surface height that marks the onset of non-planar film growth.

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“…We simulate a InAs pyramid structure, the width of the QD base is 12.4 nm and the height of the QD is 6.2 nm, for the constant effective mass model m* n =0.024m 0 , m* p,h =0.4m 0 [10] and (V in =0.0). This pyramid is embedded in a GaAs cuboid matrix with a size of (24.8×24.8×18.6) nm, for the constant effective mass model m* n =0.067m 0 , m* p,h =0.5m 0 and (V out =0.7).…”

Section: Simulation and Resultsmentioning

confidence: 99%