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Excitonic binding energy EXb of c-plane In0.2Ga0.8N/GaN QDs. The data are shown for the VCA case and for the five different random alloy configurations.
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We analyze the potential of the c -plane InGaN/GaN quantum dots for polarization entangled photon emission by means of an atomistic many-body framework. Special attention is paid to the impact of random alloy fluctuations on the excitonic fine structure and the excitonic binding energy. Our calculations show that c -plane InGaN/GaN quantum dots are...
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Citations
... light emitting diodes (LEDs)) and non-classical light sources (e.g. entangled photon emitters) [3][4][5][6][7]. It has been shown, both in experiment and theory, that the semiconductor alloy indium gallium nitride ((In,Ga)N) is particularly prone to alloy induced carrier localization effects. ...
Light emitters based on the semiconductor alloy aluminium gallium nitride ((Al,Ga)N) have gained significant attention in recent years due to their potential for a wide range of applications in the ultraviolet (UV) spectral window. However, current state-of-the-art (Al,Ga)N light emitters exhibit very low internal quantum efficiencies (IQEs). Therefore, understanding the fundamental electronic and optical properties of (Al,Ga)N-based quantum wells is key to improving the IQE. Here, we target the electronic and optical properties of c-plane AlxGa 1-x N/AlN quantum wells by means of an empirical atomistic tight-binding model. Special attention is paid to the impact of random alloy fluctuations on the results as well as the Al content x in the well. We find that across the studied Al content range (from 10% to 75% Al) strong hole wave function localization effects are observed. Additionally, with increasing Al content, electron wave functions may also start to exhibit carrier localization features. Overall, our investigations on the electronic structure of c-plane AlxGa1 -x N/AlN quantum wells reveal that already random alloy fluctuations are sufficient to lead to (strong) carrier localization effects. Furthermore, our results indicate that random alloy fluctuations impact the degree of optical polarization in c-plane AlxGa 1-x N quantum wells. We find that the switching from transverse electric to transverse magnetic light polarization occurs at higher Al contents in the atomistic calculation, which accounts for random alloy fluctuations, compared to the widely used virtual crystal approximation approach. This observation is important for light extraction efficiencies in (Al,Ga)N-based light emitting diodes operating in the deep UV.
... First, they feature a large binding energy (20 meV in bulk GaN) [10]. This makes excitons potentially stable at room temperature, opening the question of their influence on classical light emitters [i.e., light emitting diodes (LEDs)] and their possible use in quantum devices [11][12][13][14][15][16][17][18]. Second, and crucially, the random alloy disorder in III-nitride heterostructures with ternary compounds (e.g., InGaN, AlGaN, AlInN) results in energy fluctuations of tens of millielectronvolts (meV) across a few nanometers, which decorrelate the electron-hole relative motion. ...
... In general, it is concluded that holes are tightly localized by disorder, whereas electrons are nearly free (i.e., with a large lateral extent in the QW plane). A few studies have explored the effect of the Coulomb interaction in InGaN quantum dots and wells [18,[25][26][27] with a model that seeks to reconstructs the excitonic wave function using a basis of free-particle states (an approach, however, whose accuracy has not been fully established). Recently, one of the present authors presented a method to solve the 6D problem directly and showed that considering the Coulomb interaction was essential to explain the radiative properties of InGaN LEDs [28]. ...
... In addition to simple optical transitions, another important topic is the possible use of these localized excitonic states to generate entangled photon pairs from biexciton recombinations, with applications in quantum optics. As emphasized in Ref. [18], in the case of InGaN quantum dots, this is predicated both on the magnitude of the exciton exchange energy and on the polarization selection rules of the emitted light. ...
Excitons in InGaN quantum wells are investigated numerically, considering random alloy disorder and Coulomb interaction on equal footing in the Schrödinger equation. Their statistical properties are systemically explored as a function of the quantum well thickness and composition, revealing a complex competition between disorder-induced carrier localization, Coulomb attraction, and field-induced wave function separation. This results in a class of semiconductor quasiparticle with hybrid properties in between hydrogenoid excitons and disorder-localized free particles. Exciton screening by free carriers is investigated and shows distinct behavior from the screening of bulk excitons. Finally, a highly accurate approximate solution of the excitonic Schrödinger equation, with reduced numerical complexity, is introduced.
... light emitting diodes (LEDs)) and non-classical light sources (e.g. entangled photon emitters) [3][4][5][6][7]. It has been shown, both in experiment and theory, that the semiconductor alloy indium gallium nitride ((In,Ga)N) is particularly prone to alloy induced carrier localization effects. ...
Light emitters based on the semiconductor alloy aluminium gallium nitride ((Al,Ga)N) have gained significant attention in recent years due to their potential for a wide range of applications in the ultraviolet (UV) spectral window. However, current state-of-the-art (Al,Ga)N light emitters exhibit very low internal quantum efficiencies (IQEs). Therefore, understanding the fundamental electronic and optical properties of (Al,Ga)N-based quantum wells is key to improving the IQE. Here, we target the electronic and optical properties of c-plane Al$_x$Ga$_{1-x}$N/AlN quantum wells by means of an empirical atomistic tight-binding model. Special attention is paid to the impact of random alloy fluctuations on the results as well as the aluminium content x in the well. We find that across the studied Al content range (from 10% to 75% Al) strong hole wave function localization effects are observed. Additionally, with increasing Al content, electron wave functions start also to exhibit carrier localization features. Overall, our investigations on the electronic structure of c-plane Al$_x$Ga$_{1-x}$N/AlN quantum wells reveal that already random alloy fluctuations are sufficient to lead to (strong) carrier localization effects. Furthermore, our results indicate that random alloy fluctuations impact the degree of optical polarization in c-plane Al$_x$Ga$_{1-x}$N quantum wells. We find that the switching from transverse electric to transverse magnetic light polarization occurs at higher Al contents in the atomistic calculation, which accounts for random alloy fluctuations, when compared to the outcome of widely used virtual crystal approximations. This observation is important for light extraction efficiencies in (Al,Ga)N-based light emitting diodes operating in the deep UV.
... Epitaxial growth of GaN NWs on lattice-mismatched Si substrates makes it possible to obtain exceptional crystal quality in NWs [5,6] while providing an opportunity to use Si as the ohmic contact for GaN [7] and develop III-N-based UV and visible LEDs integrated with a Si electronic platform [8,9]. Single-and entangled-photon sources based on III-N materials on silicon can be used as building blocks in quantum networks and hold promise for applications in quantum informatics and telecommunications [1,[10][11][12]. ...
GaN nanowires were grown using selective area plasma-assisted molecular beam epitaxy on SiOx/Si(111) substrates patterned with microsphere lithography. For the first time, the temperature–Ga/N2 flux ratio map was established for selective area epitaxy of GaN nanowires. It is shown that the growth selectivity for GaN nanowires without any parasitic growth on a silica mask can be obtained in a relatively narrow range of substrate temperatures and Ga/N2 flux ratios. A model was developed that explains the selective growth range, which appeared to be highly sensitive to the growth temperature and Ga flux, as well as to the radius and pitch of the patterned pinholes. High crystal quality in the GaN nanowires was confirmed through low-temperature photoluminescence measurements.
... As shown in figures 6(d) and (e), the spin-up and spin-down results obtained by the Hubbard method do not differ much from those obtained by the tight-binding method. Electron-hole attractive interactions as well as excitonic states have been well studied in a number of systems [27][28][29]. In InSe-QDs, the electron-electron repulsive interactions have the opposite effect to the electron-hole attractive interactions. ...
The novel two-dimensional (2D) semiconductor, InSe, with tunable band gap and high electron mobility have attracted increasing research interest. In this work, we demonstrate theoretically
the strong geometry confinement in InSe quantum dots (QD) and manipulate their electronic and optical properties using QD shape and external field. The electronic energy levels, density of states,
probability density of states and magneto-optical absorption spectra, are calculated by utilizing the tight-binding (TB) method with coulomb interaction in Hubbard model. In contrast to other 2D materials, e.g., phosphorene, InSe-QDs exhibit distinct features as (1) edge states appear in the bottom of the conduction band regardless of the shapes of InSe-QDs. (2) The edge states are mainly provided by the In atoms at the both armchair and zigzag edges in InSe-QDs. (3) Optical gap is distinct from band gap. The rectangular InSe-QDs produce anisotropic optical absorption spectra, whereas hexagonal and triangular InSe-QDs produce isotropic absorption spectra. The applied magnetic field would weaken this anisotropy.
... This means that our first authors will get all of the benefits that open access brings (including maximum visibility, reach and impact) without paying a thing! In the meantime I very much hope you enjoy this first issue, which includes research articles on single photon sources based on hexagonal boron nitride [1], InGaN self-assembled quantum dots [2], and nitrogenvacancy colour centres in diamond [3], plus articles on the theory of g-tensor resonances for spin readout [4] and on strong coupling of solid state spins using magnons [5]. The issue also includes a perspective article by Mark Holmes and Yasuhiko Arakawa on progress towards non-cryogenic photonic quantum technologies [6]. ...
Developed in close consultation with the research community, Materials for Quantum Technology is a unique multidisciplinary, open access journal that recognises the significant long-term contribution materials science will have in overcoming wide-ranging challenges associated with realising future real-world quantum technologies. This editorial introduces the goals of the journal and describes how it will add to the publishing landscape.
Controlling the site, size, and shape of group III‐nitride quantum dots (QDs) is critical for the development of mass‐producible single‐photon sources for scalable quantum technologies operable at room temperature. Herein, a methodology is proposed for fabricating high‐purity single QD emitters by controlling site‐controlled GaN micro‐pyramid structures with a high degree of uniformity and symmetry. To achieve a uniformly grown, hexagonally symmetric micro‐pyramid array, the H2/N2 carrier gas ratio, growth temperature, and V/III ratio are controlled to attain self‐limited growth regime and self‐limited width at the GaN pyramid apex. A thin InGaN layer is consecutively grown on a pyramid array under the growth condition for enhancing the growth rate anisotropy to hinder the growth of InGaN quantum wells (QWs) at semi‐polar facets. As a result, single‐photon emission is observed from apex QD with suppressed background side QW emission while maintaining more than 90% high hexagonal QD symmetry over the large area of the wafer. Micro pyramid structures have small and finite size of self‐limited width by growing self‐limited growth mechanisms. After growing a single active layer by adjusting growth conditions, a uniform array of self‐limited pyramid with a symmetric quantum dot on its pyramid apex can be achieved.
