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Calculated absorption spectra for a photon polarization along ͓ Ϫ 110 ͔ ͑ dashed curve ͒ and along ͓ 110 ͔ ͑ continous curve ͒ for unstrained interfaces ͑ a ͒ and strained ͑ b ͒ interfaces, compared to the experimental results taken from Ref. 3 ͑ c ͒ .
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In this paper we study the electronic and optical properties of (In0.5Ga0.5As)n/(InP)n superlattices, where the Ga0.5In0.5As alloy is described both through the virtual crystal approximation (VCA) and through an appropriate ordered ternary structure. By first-principles calculations of the dielectric tensor elements we address the issue of the gian...
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... we have calculated the absorption coefficient Eq. 2 for the (MAs) 12 (InP) 12 superlattice. We have used for the calculation thirteen k points in the IBZ. The calcu- lated () has been dressed by a Gaussian broadening of 30 meV. The spectrum for the unrelaxed (MAs) 12 (InP) 12 super- lattice in the energy range of the two transitions is given in Fig. 5a, where we see the substantial superposition of the two curves corresponding to the two polarization directions along 110 and 110, respectively. The corresponding polarization rate P(), Eq. 1, is small, about 2%. The be- havior of P() in the energy range between the first and second transitions agrees with the experimental result but ...
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... of the two curves corresponding to the two polarization directions along 110 and 110, respectively. The corresponding polarization rate P(), Eq. 1, is small, about 2%. The be- havior of P() in the energy range between the first and second transitions agrees with the experimental result but its value is significantly underestimated. In Fig. 5b we show the absorption coefficient relative to the relaxed system. The absorption peaks corresponding to the two transitions are now fully resolved. Again, absorption corresponding to a polarization vector along the 110 direction selects one tran- sition, while absorption corresponding to a polarization vec- tor along 110 ''sees'' only ...
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... only the other transition. The corre- sponding polarization rate is now larger, about 15%. It is increased by an order of magnitude. Thus, in our model which still neglects spin-orbit interaction, the mechanism of the anisotropy is due entirely to the further crystal field split- ting of the V1 and V2 hole states. We compare the spectrum of Fig. 5b with the experimental absorption spectrum given in Fig. 5c. The experimental result has been rigidly shifted by 325 meV towards lower energies to account for the the- oretical LDA underestimation of the fundamental gap. There is an interesting similarity between the two spectra, both in shape and intensity for polarizations along 110 ...
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... rate is now larger, about 15%. It is increased by an order of magnitude. Thus, in our model which still neglects spin-orbit interaction, the mechanism of the anisotropy is due entirely to the further crystal field split- ting of the V1 and V2 hole states. We compare the spectrum of Fig. 5b with the experimental absorption spectrum given in Fig. 5c. The experimental result has been rigidly shifted by 325 meV towards lower energies to account for the the- oretical LDA underestimation of the fundamental gap. There is an interesting similarity between the two spectra, both in shape and intensity for polarizations along 110 and 110. The shift between the two absorption features ...
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... Owing to this difference, the NCA SL system such as GaAs/InP has been intensively studied in the past decade to explore interface related electronic and optical properties. [4][5][6][7] The most different features exhibited by CA and NCA SLs are seen in their optical properties. It has been experimentally verified that in the GaAs/InP NCA system a giant in-plane anisotropy ͑or polarization͒ in the optical absorption of light polarized along the ͓110͔ and ͓110͔ directions 5,6 occurs while CA SLs do not show any in-plane anisotropy of their optical absorption. ...
... It was shown previously that the MIA effect due to the low C 2v point-group symmetry causes an optical anisotropy with respect to the light polarization direction in the NCA SLs. [5][6][7] To observe a pronounced optical anisotropy, the light polarization direction is normally set as the ͓110͔ and ͓110͔ directions in the experiment, 5,6 which will become clear in the following. In our numerical calculation, we vary ⑀ over all the in-plane polarization angles ͑0 ϳ 2͒ and calculate the squared optical matrix elements for the test InAs/GaSb SL as a function of . ...
We theoretically investigate the intrinsic optical anisotropy or polarization induced by the microscopic interface asymmetry (MIA) in no-common-atom (NCA) InAs/GaSb superlattices (SLs) grown along the [001] direction. The eight-band K⋅P model is used to calculate the electronic band structures and incorporates the MIA effect. A Boltzmann equation approach is employed to calculate the optical properties. We found that in NCA InAs/GaSb SLs, the MIA effect causes a large in-plane optical anisotropy for linearly polarized light and the largest anisotropy occurs for light polarized along the [110] and [11̅ 0] directions. The relative difference between the optical-absorption coefficient for [110]-polarized light and that for [11̅ 0]-polarized light is found to be larger than 50%. The dependence of the in-plane optical anisotropy on temperature, photoexcited carrier density, and layer width is examined in detail. This study is important for optical devices which require the polarization control and selectivity.
... The only case that cannot be modelled is when a common-atom heterostructure has a C 2v symmetry due to different bond orientation at the interfaces. The proper symmetry reproduction will allow the study of effects due to the reduced symmetry, such as the presence of optical anisotropy [28,29], the mixing of heavy-hole and light-hole states on top of the valence band [8,30], and the spin splittings appearing in the band structure of zinc-blende heterostructures, which is shown in the rest of this paper. direction and with a well thickness of 10 monolayers (30.5 Å), with the BIA terms included. ...
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... Thus one can delineate the role of bulk inversion asymmetry vs. structure inversion asymmetry, layer asymmetry vs. interface asymmetry, etc. This model also provides a straightforward and easy to implement tool for studying reduced symmetry effects, such as the presence of optical anisotropy 45,46 , and the mixing of heavy hole and light hole states at the zone center 10,47 in QWs and superlattices. Some of these works have followed the alternative approach of introducing interface parameters to describe the lowering of symmetry respect to the standard EMA formalism 45,47,48 . ...
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We study using first-principle calculations the electronic and optical properties of In0.5Ga0.5As/InP and In0.5Al0.5As/InP superlattices, where the InGaAs and InAlAs alloys are described through an appropriate ordered ternary structure. The calculated electronic properties show that the substitution of Ga with Al originate an opening of the band gap from the infrared to the near visible and a transformation of the band alignment from type I to type II. Through the analysis of the optical properties we discuss successfully the giant polarization anisotropy observed in these systems.
We use extended-basis empirical tight-binding calculations and examine the anisotropy of the refractive index in ultrashort-period superlattices of materials sharing no common atom. We find that a strong birefringence can be engineered in these articial semiconductors, allowing phase matching for frequency difference generation. The prominent role of epitaxial constraint and bond-length alternation is evidenced.
A new attempt to solve the phase matching problem for semiconductor-based frequency conversion devices, based on the implementation of intrinsic birefringence in artificial materials, is discussed. The first results concerning the growth and characterization of ultrashort period superlattices are presented. To cite this article: J.-M. Jancu et al., C. R. Physique 8 (2007).
Abrupt InAs/GaSb superlattices have In-Sb and Ga-As interfacial chemical bonds that are not present in the constituent materials InAs and GaSb. We study the effect of interfacial atomic mixing on the electronic structure of such superlattices, including electron and hole energies and wave function localization, interband transition energies, and dipole matrix elements. We combine an empirical pseudopotential method for describing the electronic structure with two different structural models of interfacial disorder. First, we use the “single-layer disorder” model and change in a continous way the composition of the interfacial bonds. Second, we study interfacial atomic segregation using a layer-by-layer kinetic model of molecular beam epitaxy growth, fit to the observed scanning tunneling microscopy segregation profiles. The growth model provides a detailed structural model of segregated InAs/GaSb superlattices with atomic resolution. The application of the empirical pseudopotential method to such structures reveals remarkable electronic consequences of segregation, among them a large blueshift of the band gap. This result explains the surprising gap increase with growth temperature observed for similar structures. In particular we find that (i) superlattices with only In-Sb interfacial bonds have lower band gaps (by 50 meV) than superlattices with only Ga-As interfacial bonds. (ii) Heavy-hole–to–electron transition energies increase with the number of Ga-As interfacial bonds more than light-hole–to–electron transition energies. (iii) The heavy-hole hh1 wave functions show a strong localization on the In-Sb interfacial bonds. The heavy-hole wave functions have very different amplitudes on the Ga-As interface and on the In-Sb interface. (iv) Sb segregates at InAs-on-GaSb growth, whereas As and In segregate at GaSb-on-InAs growth, but Ga does not segregate. (v) The segregation of Sb and In induces a blueshift in the band gap. (vi) There is an in-plane polarization anisotropy due to the low symmetry of the no-common-atom InAs/GaSb superlattice. This anisotropy is reduced by interfacial segregation.
Raman spectra of In0.80Ga0.20As/(AlAs)/AlAs056Sb0.44 quantum wells (QWs) grown on (0 0 1)-InP substrates by molecular beam epitaxy were measured in backscattering along and directions, i.e. from (0 0 1) grown and (1 1 0) cleaved surfaces, with microprobes. Confined longitudinal-optic (LO) and transverse-optic (TO) phonons with wave vector q either parallel or normal to the Z axis were studied in all the independent scattering geometries. The Raman scattering spectra from (0 0 1) surfaces show two-mode behavior in the InGaAs band, while single mode behavior is confirmed in the AlAsSb band, consistent with the previous results. The GaAs-like LO- phonon peak splits into two peaks that can be attributed to the confined GaAs-like LO-phonon mode and the intermediate frequency plasmon-LO-phonon coupled mode. A drastic change in the Raman spectra is observed when the transferred momentum is changed from the Z-axis to x-axis. The Raman spectra in the geometry are dominated by TO-confined phonons, whereas LO-confined phonons are dominated in the geometry, consistent with the selection rules, although in other configurations no signals are observed inconsistent with the selection rules.
