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1.
Nature ; 631(8020): 307-312, 2024 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-38898280

RESUMEN

Spin accumulation in semiconductor structures at room temperature and without magnetic fields is key to enable a broader range of optoelectronic functionality1. Current efforts are limited owing to inherent inefficiencies associated with spin injection across semiconductor interfaces2. Here we demonstrate spin injection across chiral halide perovskite/III-V interfaces achieving spin accumulation in a standard semiconductor III-V (AlxGa1-x)0.5In0.5P multiple quantum well light-emitting diode. The spin accumulation in the multiple quantum well is detected through emission of circularly polarized light with a degree of polarization of up to 15 ± 4%. The chiral perovskite/III-V interface was characterized with X-ray photoelectron spectroscopy, cross-sectional scanning Kelvin probe force microscopy and cross-sectional transmission electron microscopy imaging, showing a clean semiconductor/semiconductor interface at which the Fermi level can equilibrate. These findings demonstrate that chiral perovskite semiconductors can transform well-developed semiconductor platforms into ones that can also control spin.

2.
J Microsc ; 284(2): 132-141, 2021 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-34223644

RESUMEN

Precession electron diffraction (PED) was used to measure the long-range order parameter in lattice-mismatched AlInP epitaxial films under investigation for solid-state-lighting applications. Both double- and single-variant films grown at 620, 650 and 680 °C were analysed in TEM cross-section. PED patterns were acquired in selected-area-diffraction mode through external microscope control using serial acquisition, which allows inline image processing. The integrated peak intensities from experimental patterns were fit using dynamical simulations of diffraction from the ordered domain structures. Included in the structure-factor calculations were mean atomic displacements of the anions (P) due to ordering, which were found by valence-force-field calculations to have a nearly linear dependence on order parameter. A maximum order parameter of S = 0.36 was measured for a double-variant specimen grown at 650 °C.


Compound semiconductors play a central role in current light-emitting diodes (LED) technology, but improvements in the red- and amber-emitting components are needed. The semiconductor alloy AlInP offers advantages over incumbent materials by making use of an arrangement in the crystal structure, called 'atomic ordering', that occurs spontaneously under certain deposition conditions. Quantitative measurement of the extent to which the ordering phenomenon occurs is needed to fully exploit the properties of the ordered material. Transmission electron diffraction offers a means to directly probe the ordered structures, but the quantification of electron-diffraction data has been a long-standing challenge, due to multiple scattering processes, referred to as 'dynamical' diffraction. The method of precession electron diffraction (PED) addresses this problem and has found numerous applications in crystallography. We have applied PED to ordered AlInP films, using computer-controlled acquisition to perform alignments and construct data sets during collection. A model of the microscopic, ordered domain structure was developed to compare the diffraction data to simulations. Samples grown at different temperatures, and ordered along either one or two directions, were evaluated. The strongest ordering was observed in a sample grown at 650 °C with ordering along two directions.

3.
Sci Rep ; 7(1): 8516, 2017 08 17.
Artículo en Inglés | MEDLINE | ID: mdl-28819295

RESUMEN

Integrating different semiconductor materials into an epitaxial device structure offers additional degrees of freedom to select for optimal material properties in each layer. However, interfaces between materials with different valences (i.e. III-V, II-VI and IV semiconductors) can be difficult to form with high quality. Using ZnSe/GaAs as a model system, we explore the use of ultraviolet (UV) illumination during heterovalent interface growth by molecular beam epitaxy as a way to modify the interface properties. We find that UV illumination alters the mixture of chemical bonds at the interface, permitting the formation of Ga-Se bonds that help to passivate the underlying GaAs layer. Illumination also helps to reduce defects in the ZnSe epilayer. These results suggest that moderate UV illumination during growth may be used as a way to improve the optical properties of both the GaAs and ZnSe layers on either side of the interface.

4.
Opt Lett ; 42(6): 1165-1168, 2017 Mar 15.
Artículo en Inglés | MEDLINE | ID: mdl-28295074

RESUMEN

We demonstrate the condensation of microcavity polaritons with a very sharp threshold occurring at a two orders of magnitude pump intensity lower than previous demonstrations of condensation. The long cavity lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of coherent light at a lower threshold than traditional lasing, and these results indicate some considerations for optimizing designs for lower thresholds.

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