Spatially Resolved Investigation of the Bandgap Variation across a β-(AlxGa1–x)2O3/β-Ga2O3 Interface by STEM–VEELS

Chmielewski, Adrian; Deng, Ziling; Moradifar, Parivash; Miao, Leixin; Zhang, Yuewei; Mauze, Akhil; Lopez, Kleyser Agueda; Windl, Wolfgang; Alem, Nasim

doi:10.1021/acsaelm.1c00824

Cited by 3 publications

(2 citation statements)

References 63 publications

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“…However, only a few studies have focused on the characterization of atomic scale defects in β-(Al x Ga 1– x ) 2 O 3 heterostructures using scanning transmission electron microscopy (STEM). STEM is a powerful tool to directly visualize the crystal structure of the studied material at an atomic scale using sub-Ångstrom resolution imaging. − Using high-angle annular dark-field (HAADF) and annular bright-field (ABF) detectors, it is possible to form images from Ga atoms and lighter elements like O atoms provided that the crystal is oriented in a proper direction. Bhuiyan et al studied (010) β-(Al x Ga 1– x ) 2 O 3 thin films grown on (010) β-Ga 2 O 3 substrates via MOCVD with up to 40% of Al concentration using high-resolution HAADF-STEM .…”

Section: Introductionmentioning

confidence: 99%

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film

Chmielewski

Deng²,

Duarte-Ruiz

et al. 2023

ACS Appl. Mater. Interfaces

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Alloying Al2O3 with Ga2O3 to form β-(Al x Ga1–x )2O3 opens the door to a large number of new possibilities for the fabrication of devices with tunable properties in many high-performance applications such as optoelectronics, sensing systems, and high-power electronics. Often, the properties of these devices are impacted by defects induced during the growth process. In this work, we uncover the crystal structure of a β-(Al0.2Ga0.8)2O3/β-Ga2O3 interface grown by molecular beam epitaxy. In particular, we determine Al coordination and the stability of Al and Ga interstitials and their effect on the electronic structure of the material by means of scanning transmission electron microscopy combined with density functional theory. Al atoms can substitutionally occupy both octahedral and tetrahedral sites. The atomic structure of the β-(Al0.2Ga0.8)2O3/β-Ga2O3 interface additionally shows Al and Ga interstitials located between neighboring tetrahedrally coordinated cation sites, whose stability will depend on the number of surrounding Al atoms. The presence of Al atoms near interstitials leads to structural distortions in the lattice and creates interstitial-divacancy complexes that will eventually form deep-level states below the conduction band (E c) at E c −1.25 eV, E c −1.68 eV, E c −1.78 eV, E c −1.83 eV, and E c −1.86 eV for a Ga interstitial surrounded by zero, one, two, three, and four Al atoms, respectively. These findings bring new insight toward the fabrication of tunable β-(Al x Ga1–x )2O3 heterostructure-based devices with controlled electronic properties.

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Section: Introductionmentioning

confidence: 99%

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film

Chmielewski

Deng²,

Duarte-Ruiz

et al. 2023

ACS Appl. Mater. Interfaces

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“…), defect-induced strain, grain boundaries, heterointerfaces, impurity dopants, and edge configurations (zigzag, armchair, etc.). These atomic-structure variations can introduce scattering pathways (point defects), limit carrier mobility, and create trapped states (grain boundaries and heterointerfaces) , as well as vary the bonding configuration and local charge distribution (impurity dopants). − However, defects and imperfections are not always detrimental. − For example, lattice disorder resulting from impurities and defects can lead to electron localization, known as Anderson localization, which is a crucial mechanism for metal-to-insulator transitions in condensed matter. , Additionally, atomic-scale defects can also be bright sources of single photons. For example, the negatively charged nitrogen vacancy center (NV – ) in diamond can serve as a qubit with long coherence times or as a single-photon quantum emitter .…”

Section: Introductionmentioning

confidence: 99%

Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy

Moradifar,

Liu,

Shi

et al. 2023

Chem. Rev.

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Quantum materials are driving a technology revolution in sensing, communication, and computing, while simultaneously testing many core theories of the past century. Materials such as topological insulators, complex oxides, superconductors, quantum dots, color center-hosting semiconductors, and other types of strongly correlated materials can exhibit exotic properties such as edge conductivity, multiferroicity, magnetoresistance, superconductivity, single photon emission, and optical-spin locking. These emergent properties arise and depend strongly on the material’s detailed atomic-scale structure, including atomic defects, dopants, and lattice stacking. In this review, we describe how progress in the field of electron microscopy (EM), including in situ and in operando EM, can accelerate advances in quantum materials and quantum excitations. We begin by describing fundamental EM principles and operation modes. We then discuss various EM methods such as (i) EM spectroscopies, including electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and electron energy gain spectroscopy (EEGS); (ii) four-dimensional scanning transmission electron microscopy (4D-STEM); (iii) dynamic and ultrafast EM (UEM); (iv) complementary ultrafast spectroscopies (UED, XFEL); and (v) atomic electron tomography (AET). We describe how these methods could inform structure–function relations in quantum materials down to the picometer scale and femtosecond time resolution, and how they enable precision positioning of atomic defects and high-resolution manipulation of quantum materials. For each method, we also describe existing limitations to solve open quantum mechanical questions, and how they might be addressed to accelerate progress. Among numerous notable results, our review highlights how EM is enabling identification of the 3D structure of quantum defects; measuring reversible and metastable dynamics of quantum excitations; mapping exciton states and single photon emission; measuring nanoscale thermal transport and coupled excitation dynamics; and measuring the internal electric field and charge density distribution of quantum heterointerfaces- all at the quantum materials’ intrinsic atomic and near atomic-length scale. We conclude by describing open challenges for the future, including achieving stable sample holders for ultralow temperature (below 10K) atomic-scale spatial resolution, stable spectrometers that enable meV energy resolution, and high-resolution, dynamic mapping of magnetic and spin fields. With atomic manipulation and ultrafast characterization enabled by EM, quantum materials will be poised to integrate into many of the sustainable and energy-efficient technologies needed for the 21st century.

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Understanding Dislocation and Deformation Structure In Monoclinic Ultrawide Bandgap Semiconductor β-Ga2O3 Under High-Stress

Balog,

Bisht,

Jesenovec

et al. 2024

Microscopy and Microanalysis

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Spatially Resolved Investigation of the Bandgap Variation across a β-(Al_xGa_1–x)₂O₃/β-Ga₂O₃ Interface by STEM–VEELS

Cited by 3 publications

References 63 publications

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film

Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy

Understanding Dislocation and Deformation Structure In Monoclinic Ultrawide Bandgap Semiconductor β-Ga2O3 Under High-Stress

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Spatially Resolved Investigation of the Bandgap Variation across a β-(AlxGa1–x)2O3/β-Ga2O3 Interface by STEM–VEELS

Cited by 3 publications

References 63 publications

Al Coordination and Ga Interstitial Stability in a β-(Al0.2Ga0.8)2O3 Thin Film

Al Coordination and Ga Interstitial Stability in a β-(Al0.2Ga0.8)2O3 Thin Film

Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy

Understanding Dislocation and Deformation Structure In Monoclinic Ultrawide Bandgap Semiconductor β-Ga2O3 Under High-Stress

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Product

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Spatially Resolved Investigation of the Bandgap Variation across a β-(Al_xGa_1–x)₂O₃/β-Ga₂O₃ Interface by STEM–VEELS

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film

Al Coordination and Ga Interstitial Stability in a β-(Al_0.2Ga_0.8)₂O₃ Thin Film