Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates
The first part of this work evaluates Al-doped ZnO (AZO) as an optically transparent top-gate material for studies on semiconductor quantum dots. In comparison with conventional Ti gates, samples with AZO gates demonstrate a more than three times higher intensity in the quantum dot emission under co...
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2024-10-01
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| author | Ahmed Alshaikh Jun Peng Robert Zierold Robert H. Blick Christian Heyn |
| author_facet | Ahmed Alshaikh Jun Peng Robert Zierold Robert H. Blick Christian Heyn |
| author_sort | Ahmed Alshaikh |
| collection | DOAJ |
| description | The first part of this work evaluates Al-doped ZnO (AZO) as an optically transparent top-gate material for studies on semiconductor quantum dots. In comparison with conventional Ti gates, samples with AZO gates demonstrate a more than three times higher intensity in the quantum dot emission under comparable excitation conditions. On the other hand, charges inside a process-induced oxide layer at the interface to the semiconductor cause artifacts at gate voltages above <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mo>≈</mo></mrow></semantics></math></inline-formula> 1 V. The second part describes an optical and simulation study of a vertical electric-field (<i>F</i>)-induced switching from a strong to an asymmetric strong–weak confinement in GaAs cone-shell quantum dots (CSQDs), where the charge carrier probability densities are localized on the surface of a cone. These experiments are performed at low <i>U</i> and show no indications of an influence of interface charges. For a large <i>F</i>, the measured radiative lifetimes are substantially shorter compared with simulation results. We attribute this discrepancy to an <i>F</i>-induced transformation of the shape of the hole probability density. In detail, an increasing <i>F</i> pushes the hole into the wing part of a CSQD, where it forms a quantum ring. Accordingly, the confinement of the hole is changed from strong, which is assumed in the simulations, to weak, where the local radius is larger than the bulk exciton Bohr radius. In contrast to the hole, an increasing <i>F</i> pushes the electron into the CSQD tip, where it remains in a strong confinement. This means the radiative lifetime for large <i>F</i> is given by an asymmetric confinement with a strongly confined electron and a hole in a weak confinement. To our knowledge, this asymmetric strong–weak confinement represents a novel kind of quantum mechanical confinement and has not been observed so far. Furthermore, the observed weak confinement for the hole represents a confirmation of the theoretically predicted transformation of the hole probability density from a quantum dot into a quantum ring. For such quantum rings, application as storage for photo-excited charge carriers is predicted, which can be interesting for future quantum photonic integrated circuits. |
| format | Article |
| id | doaj-art-e2b243d18e574fcbb56cb83ee3c3bd8f |
| institution | Kabale University |
| issn | 2079-4991 |
| language | English |
| publishDate | 2024-10-01 |
| publisher | MDPI AG |
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| series | Nanomaterials |
| spelling | doaj-art-e2b243d18e574fcbb56cb83ee3c3bd8f2024-11-08T14:38:48ZengMDPI AGNanomaterials2079-49912024-10-011421171210.3390/nano14211712Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO GatesAhmed Alshaikh0Jun Peng1Robert Zierold2Robert H. Blick3Christian Heyn4Center for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyCenter for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyCenter for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyCenter for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyCenter for Hybrid Nanostructures (CHyN), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyThe first part of this work evaluates Al-doped ZnO (AZO) as an optically transparent top-gate material for studies on semiconductor quantum dots. In comparison with conventional Ti gates, samples with AZO gates demonstrate a more than three times higher intensity in the quantum dot emission under comparable excitation conditions. On the other hand, charges inside a process-induced oxide layer at the interface to the semiconductor cause artifacts at gate voltages above <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mo>≈</mo></mrow></semantics></math></inline-formula> 1 V. The second part describes an optical and simulation study of a vertical electric-field (<i>F</i>)-induced switching from a strong to an asymmetric strong–weak confinement in GaAs cone-shell quantum dots (CSQDs), where the charge carrier probability densities are localized on the surface of a cone. These experiments are performed at low <i>U</i> and show no indications of an influence of interface charges. For a large <i>F</i>, the measured radiative lifetimes are substantially shorter compared with simulation results. We attribute this discrepancy to an <i>F</i>-induced transformation of the shape of the hole probability density. In detail, an increasing <i>F</i> pushes the hole into the wing part of a CSQD, where it forms a quantum ring. Accordingly, the confinement of the hole is changed from strong, which is assumed in the simulations, to weak, where the local radius is larger than the bulk exciton Bohr radius. In contrast to the hole, an increasing <i>F</i> pushes the electron into the CSQD tip, where it remains in a strong confinement. This means the radiative lifetime for large <i>F</i> is given by an asymmetric confinement with a strongly confined electron and a hole in a weak confinement. To our knowledge, this asymmetric strong–weak confinement represents a novel kind of quantum mechanical confinement and has not been observed so far. Furthermore, the observed weak confinement for the hole represents a confirmation of the theoretically predicted transformation of the hole probability density from a quantum dot into a quantum ring. For such quantum rings, application as storage for photo-excited charge carriers is predicted, which can be interesting for future quantum photonic integrated circuits.https://www.mdpi.com/2079-4991/14/21/1712Al-doped ZnOGaAs quantum dotphotoluminescenceexcitonlifetimeStark shift |
| spellingShingle | Ahmed Alshaikh Jun Peng Robert Zierold Robert H. Blick Christian Heyn Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates Nanomaterials Al-doped ZnO GaAs quantum dot photoluminescence exciton lifetime Stark shift |
| title | Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates |
| title_full | Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates |
| title_fullStr | Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates |
| title_full_unstemmed | Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates |
| title_short | Vertical Electric-Field-Induced Switching from Strong to Asymmetric Strong–Weak Confinement in GaAs Cone-Shell Quantum Dots Using Transparent Al-Doped ZnO Gates |
| title_sort | vertical electric field induced switching from strong to asymmetric strong weak confinement in gaas cone shell quantum dots using transparent al doped zno gates |
| topic | Al-doped ZnO GaAs quantum dot photoluminescence exciton lifetime Stark shift |
| url | https://www.mdpi.com/2079-4991/14/21/1712 |
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