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Start Over Author "Chen, X." Journal applied physics letters
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2. Investigation of the surface band structure and the evolution of defects in β-(AlxGa1−x)2O3.

Author

Li, J., Chen, X. H., Hao, J. G., Ren, F. F., Gu, S. L., and Ye, J. D.

Subjects
*FLUX pinning, *ELECTRON transitions, *SURFACE structure, *FERMI surfaces, *FERMI level, *X-ray photoelectron spectroscopy, *ZINC oxide films
Abstract

This study examines the electronic and luminescent properties of β-(AlxGa1−x)2O3 (0 ≤ x ≤ 0.42) thin films grown on (0001) sapphire using laser-MBE, with a focus on the evolution of defect energy levels and their impact on surface Fermi level pinning and luminescence. X-ray photoelectron spectroscopy (XPS) and cathodoluminescence (CL) have been employed to analyze surface band bending and defect evolution as a function of aluminum content. The results have revealed a pinned Fermi level at 3.6 eV above the valence band maximum despite the increase in the bandgap. The consequent upward band bending has been confirmed by a peak shift in the core level XPS. The defects that lead to the Fermi level pinning effect are attributed to E2*, which is related to a Ga vacancy or Ga vacancy-O vacancy complex. In addition, CL spectroscopy and depth-resolved CL have demonstrated consistent blue and ultraviolet emissions across the Al content range and a similar suppression of electron concentration on blue and ultraviolet emissions in β-(AlxGa1−x)2O3 and β-Ga2O3. Based on the observed evolution of defects with Al content, the blue band emission is attributed to electron transition in the donor–accepter pair. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Investigation of the surface band structure and the evolution of defects in β-(AlxGa1−x)2O3.

Author

Li, J., Chen, X. H., Hao, J. G., Ren, F. F., Gu, S. L., and Ye, J. D.

Subjects
FLUX pinning, ELECTRON transitions, SURFACE structure, FERMI surfaces, FERMI level, X-ray photoelectron spectroscopy, ZINC oxide films
Abstract

This study examines the electronic and luminescent properties of β-(AlxGa1−x)2O3 (0 ≤ x ≤ 0.42) thin films grown on (0001) sapphire using laser-MBE, with a focus on the evolution of defect energy levels and their impact on surface Fermi level pinning and luminescence. X-ray photoelectron spectroscopy (XPS) and cathodoluminescence (CL) have been employed to analyze surface band bending and defect evolution as a function of aluminum content. The results have revealed a pinned Fermi level at 3.6 eV above the valence band maximum despite the increase in the bandgap. The consequent upward band bending has been confirmed by a peak shift in the core level XPS. The defects that lead to the Fermi level pinning effect are attributed to E2*, which is related to a Ga vacancy or Ga vacancy-O vacancy complex. In addition, CL spectroscopy and depth-resolved CL have demonstrated consistent blue and ultraviolet emissions across the Al content range and a similar suppression of electron concentration on blue and ultraviolet emissions in β-(AlxGa1−x)2O3 and β-Ga2O3. Based on the observed evolution of defects with Al content, the blue band emission is attributed to electron transition in the donor–accepter pair. [ABSTRACT FROM AUTHOR]

Published
2024
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4. In-situ characterization of highly reversible phase transformation by synchrotron X-ray Laue microdiffraction

Author

Chen, X, Tamura, N, Macdowell, A, and James, RD

Subjects
Applied Physics, Engineering, Physical Sciences, Technology
Abstract

The alloy Cu25Au30Zn45 undergoes a huge first-order phase transformation (6% strain) and shows a high reversibility under thermal cycling and an unusual martensitc microstructure in sharp contrast to its nearby compositions. This alloy was discovered by systematically tuning the composition so that its lattice parameters satisfy the cofactor conditions (i.e., the kinematic conditions of compatibility between phases). It was conjectured that satisfaction of these conditions is responsible for the enhanced reversibility as well as the observed unusual fluid-like microstructure during transformation, but so far, there has been no direct evidence confirming that these observed microstructures are those predicted by the cofactor conditions. To verify this hypothesis, we use synchrotron X-ray Laue microdiffraction to measure the orientations and structural parameters of variants and phases near the austenite/martensite interface. The areas consisting of both austenite and multi-variants of martensite are scanned by microLaue diffraction. The cofactor conditions have been examined from the kinematic relation of lattice vectors across the interface. The continuity condition of the interface is precisely verified from the correspondent lattice vectors between two phases.

Published
2016

5. Searching for the causes of anomalous Advanced LIGO noise

Author

Berger, B. K., primary, Areeda, J. S., additional, Barker, J. D., additional, Effler, A., additional, Goetz, E., additional, Helmling-Cornell, A. F., additional, Lantz, B., additional, Lundgren, A. P., additional, Macleod, D. M., additional, McIver, J., additional, Mittleman, R., additional, Nguyen, P., additional, Pele, A., additional, Pham, H., additional, Rangnekar, P., additional, Rink, K., additional, Schofield, R. M. S., additional, Smith, J. R., additional, Soni, S., additional, Warner, J., additional, Abbott, R., additional, Adhikari, R. X., additional, Ananyeva, A., additional, Appert, S., additional, Arai, K., additional, Asali, Y., additional, Aston, S. M., additional, Baer, A. M., additional, Ball, M., additional, Ballmer, S. W., additional, Banagiri, S., additional, Barker, D., additional, Barsotti, L., additional, Betzwieser, J., additional, Bhattacharjee, D., additional, Billingsley, G., additional, Biscans, S., additional, Blair, C. D., additional, Blair, R. M., additional, Bode, N., additional, Booker, P., additional, Bork, R., additional, Brooks, A. F., additional, Brown, D. D., additional, Cahillane, C., additional, Chen, X., additional, Ciobanu, A. A., additional, Clara, F., additional, Compton, C. M., additional, Cooper, S. J., additional, Corley, K. R., additional, Countryman, S. T., additional, Covas, P. B., additional, Coyne, D. C., additional, Datrier, L. E. H., additional, Davis, D., additional, Di Fronzo, C., additional, Dooley, K. L., additional, Driggers, J. C., additional, Dwyer, S. E., additional, Etzel, T., additional, Evans, M., additional, Evans, T. M., additional, Feicht, J., additional, Fernandez-Galiana, A., additional, Fritschel, P., additional, Frolov, V. V., additional, Fulda, P., additional, Fyffe, M., additional, Giaime, J. A., additional, Giardina, K. D., additional, Godwin, P., additional, Gras, S., additional, Gray, C., additional, Gray, R., additional, Green, A. C., additional, Gupta, A., additional, Gustafson, E. K., additional, Gustafson, R., additional, Hanks, J., additional, Hanson, J., additional, Hasskew, R. K., additional, Heintze, M. C., additional, Holland, N. A., additional, Kandhasamy, S., additional, Karki, S., additional, Kasprzack, M., additional, Kawabe, K., additional, Kijbunchoo, N., additional, King, P. J., additional, Kissel, J. S., additional, Kumar, Rahul, additional, Landry, M., additional, Lane, B. B., additional, Laxen, M., additional, Lecoeuche, Y. K., additional, Leviton, J., additional, Liu, J., additional, Lormand, M., additional, Macas, R., additional, MacInnis, M., additional, Mansell, G. L., additional, Márka, S., additional, Márka, Z., additional, Martynov, D. V., additional, Mason, K., additional, Matichard, F., additional, Mavalvala, N., additional, McCarthy, R., additional, McClelland, D. E., additional, McCormick, S., additional, McCuller, L., additional, McRae, T., additional, Mendell, G., additional, Merfeld, K., additional, Merilh, E. L., additional, Meylahn, F., additional, Mistry, T., additional, Moreno, G., additional, Mow-Lowry, C. M., additional, Mozzon, S., additional, Mullavey, A., additional, Nelson, T. J. N., additional, Nuttall, L. K., additional, Oberling, J., additional, Oram, Richard J., additional, Osthelder, C., additional, Ottaway, D. J., additional, Overmier, H., additional, Parker, W., additional, Payne, E., additional, Penhorwood, R., additional, Perez, C. J., additional, Pirello, M., additional, Ramirez, K. E., additional, Richardson, J. W., additional, Riles, K., additional, Robertson, N. A., additional, Rollins, J. G., additional, Romel, C. L., additional, Romie, J. H., additional, Ross, M. P., additional, Ryan, K., additional, Sadecki, T., additional, Sanchez, E. J., additional, Sanchez, L. E., additional, Saravanan, T. R., additional, Savage, R. L., additional, Schaetzl, D., additional, Schnabel, R., additional, Schwartz, E., additional, Sellers, D., additional, Shaffer, T., additional, Sigg, D., additional, Slagmolen, B. J. J., additional, Sorazu, B., additional, Spencer, A. P., additional, Sun, L., additional, Szczepańczyk, M. J., additional, Thomas, M., additional, Thomas, P., additional, Thorne, K. A., additional, Toland, K., additional, Torrie, C. I., additional, Traylor, G., additional, Tse, M., additional, Vajente, G., additional, Valdes, G., additional, Vander-Hyde, D. C., additional, Veitch, P. J., additional, Venugopalan, G., additional, Viets, A. D., additional, Vorvick, C., additional, Wade, M., additional, Ward, R. L., additional, Weaver, B., additional, Weiss, R., additional, Whittle, C., additional, Willke, B., additional, Wipf, C. C., additional, Xiao, L., additional, Yamamoto, H., additional, Yu, Hang, additional, Yu, Haocun, additional, Zhang, L., additional, Zucker, M. E., additional, and Zweizig, J., additional

Published
2023
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13. Strain-driven phase manipulation of α- and κ-Ga2O3 by nanoepitaxial lateral overgrowth on embedded α-In2O3 submicron dots.

Author

Kuang, Y., Ma, T. C., Chen, X. H., Hao, J. G., Ren, F.-F., Gu, S. L., Zhang, R., Zheng, Y. D., and Ye, J. D.

Subjects
GEOMETRIC quantum phases, ELECTRONIC equipment, TRANSMISSION electron microscopy, HOMOEPITAXY, QUANTUM dots, GEOMETRIC analysis
Abstract

Heteroepitaxy of corundum-structured α-Ga2O3 and intriguing ferroelectric κ-Ga2O3 is proven as an alternative strategy to solve current challenges in heat dissipation and large-scale productivity for Ga2O3-based power electronic devices, whereas the fundamental growth dynamics and phase control of metastable Ga2O3 are still far unexplored. In this Letter, we demonstrate the strategy of strain engineering for the in situ phase manipulation of metastable Ga2O3 by embedding α-In2O3 submicrometer dots. Phase transition is modulated by the surface coverage of α-In2O3 due to the competitive growth of κ-Ga2O3 upon α-In2O3 and the homoepitaxy of α-Ga2O3 on the exposed α-Ga2O3 seed region. Upon discrete α-In2O3 submicrometer dots with a low surface coverage, the growth undergoes a nano-scale epitaxial lateral overgrowth mode, in which the selective homoepitaxy of α-Ga2O3 is dominant, and embedded α-In2O3 serves as nano-masks to prevent the threading dislocation propagation into the lateral overgrown Ga2O3 layer. In comparison, κ-Ga2O3 is energetically favorable on the interconnected α-In2O3 submicrometer dots, which are driven by the in-plane tensile strain as probed by the geometric phase analysis of transmission electron microscopy. Phase manipulation by embedded sub micrometer dots allows us to deliver high-quality Ga2O3 with well-defined phases and to conceive advanced devices with ultra-low loss, high frequency, and memorizing functionality. [ABSTRACT FROM AUTHOR]

Published
2021
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19. A self-powered solar-blind photodetector based on polyaniline/α-Ga2O3 p–n heterojunction.

Author

Sun, X. Y., Chen, X. H., Hao, J. G., Wang, Z. P., Xu, Y., Gong, H. H., Zhang, Y. J., Yu, X. X., Zhang, C. D., Ren, F.-F., Gu, S. L., Zhang, R., and Ye, J. D.

Subjects
*P-N heterojunctions, *PHOTODETECTORS, *POLYANILINES, *QUANTUM efficiency, *HYBRID systems, *VISIBLE spectra
Abstract

In this work, we demonstrated the self-powered solar-blind photodetector based on a polyaniline/α-Ga2O3 hybrid heterojunction. The resultant device exhibited distinct self-power characteristics with a peak photoresponsivity (R) of 8.2 mA/W, a UVC (UV light of wavelength range at 200–280 nm)/UVA (UV light of wavelength range at 320–400 nm) rejection ratio (R220 nm/R400 nm) of 2.97 × 104, and a response decay time (τdec) of 176 μs at zero bias. With an elevated bias to 5 V, the dark current remained in an ultralow level of 0.21 pA, while the rejection ratio and τdec were improved to be 7.13 × 104 and 153 μs, respectively, together with the corresponding external quantum efficiency of 38.4% and a detectivity of 6.63 × 1013 Jones. Thanks to the dual functions of bandpass transmission in the deep-ultraviolet spectral region and the hole spreading transport of the polyaniline layer, the responsivity to the visible light is suppressed with the negligible internal photoemission effect, thus leading to the improved rejection ratio. Furthermore, weak interface interactions in such polyaniline/α-Ga2O3 organic–inorganic hybrid systems avoid the introduction of interfacial trapping centers by lattice mismatch and the stabilization of negatively charged anions (O2−) by (−NH2)-+species in polyaniline deactivate oxygen vacancies at the α-Ga2O3 surface, both of which lead to the negligible persistent photoconductivity effect. As a result, in the aid of the interfacial built-in field, the constructed hybrid heterojunction exhibited a self-powered detecting characteristic and a fast response speed. These findings verify the feasibility of delivering high performance photodetectors by implementing the inorganic/organic hybrid bipolar device design to overcome the difficulty in p-type Ga2O3. [ABSTRACT FROM AUTHOR]

Published
2021
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22. 3 μm InAs quantum well lasers at room temperature on InP

Author

Ji, W. Y., primary, Gu, Y., additional, Zhang, J., additional, Ma, Y. J., additional, Chen, X. Y., additional, Gong, Q., additional, Huang, W. G., additional, Shi, Y. H., additional, He, G. X., additional, Huang, H., additional, and Zhang, Y. G., additional

Published
2018
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23. Band alignment and band bending at α-Ga2O3/ZnO n-n isotype hetero-interface.

Author

Chen, X. H., Chen, Y. T., Ren, F.-F., Gu, S. L., Tan, H. H., Jagadish, C., and Ye, J. D.

Subjects
*PHOTOELECTRON spectroscopy, *GALLIUM compounds, *OPTOELECTRONIC devices, *DEPTH profiling, *X-ray spectroscopy, *INTERFACE structures
Abstract

Understanding the electronic structures at the interfaces of wide bandgap oxide heterostructures is crucial for the rational design of oxide-based optoelectronic devices with novel functionality and improved performance. In this work, the electronic band diagram at a ZnO/α-Ga2O3 n-n isotype heterojunction is investigated by depth-profile x-ray photoemission spectroscopy (XPS). The directly measured valence-band offset is −0.61 ± 0.1 eV and a type-I (straddling gap) band alignment is formed at the ZnO/α-Ga2O3 heterointerface. As probed by the depth profile of core-levels and VB-XPS, the formation of an interfacial layer is observed due to Ga and Zn interdiffusion, where charged interfacial states result in the downward and upward band-bending at the ZnO and α-Ga2O3 sides, respectively. The influence of band bending and band discontinuity at the interface is confirmed by the rectifying characteristics in the Au/α-Ga2O3/ZnO heterojunction with electron accumulation at its interface. Taking the thermionic-field emission and band-to-band tunneling mechanisms into account, the simulated transport properties agrees well with the reported I-V characteristics of Au/α-Ga2O3/ZnO avalanche photodiode, a further validation of the deduced band alignment of the heterostructure. [ABSTRACT FROM AUTHOR]

Published
2019
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24. On the origin of dislocation generation and annihilation in α-Ga2O3 epilayers on sapphire.

Author

Ma, T. C., Chen, X. H., Kuang, Y., Li, L., Li, J., Kremer, F., Ren, F.-F., Gu, S. L., Zhang, R., Zheng, Y. D., Tan, H. H., Jagadish, C., and Ye, J. D.

Subjects
*EDGE dislocations, *SCREW dislocations, *TRANSMISSION electron microscopy, *THICK films, *DISLOCATION density, *SAPPHIRES
Abstract

Epitaxial film quality is critical to the success of high-performance α-Ga2O3 vertical power devices. In this work, the origins of threading dislocation generation and annihilation in thick α-Ga2O3 films heteroepitaxially grown on sapphire by the mist-CVD technique have been examined by means of high-resolution X-ray diffraction and transmission electron microscopies. By increasing the nominal thickness, screw dislocations exhibit an independent characteristic with a low density of about 1.8 × 106 cm−2, while edge dislocations propagating along the c-axis are dominant, which decrease down to 2.1 × 109 cm−2 in density for an 8 μm-thick α-Ga2O3 layer and exhibit an inverse dependence on the thickness. In the framework of the glide analytical model, parallel edge dislocations are generated at the interface due to the misfit-induced strain relaxation, while the dislocation glide and coalescence result in the annihilation and fusion behaviors. The optimal thick α-Ga2O3 with low dislocation densities may provide a prospective alternative to fully realize α-Ga2O3 power devices. [ABSTRACT FROM AUTHOR]

Published
2019
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28. Hybrid improper ferroelectricity in B-site substituted Ca3Ti2O7: The role of tolerance factor.

Author

Liu, X. Q., Chen, B. H., Lu, J. J., Hu, Z. Z., and Chen, X. M.

Subjects
FERROELECTRICITY, MAGNETOELECTRIC effect, FERROELECTRIC materials, POLARIZATION (Electricity), SPACE groups
Abstract

Hybrid improper ferroelectricity is induced by the coupling of oxygen octahedral rotation and tilting, and a promising way to create multiferroic materials with a strong magnetoelectric effect can be proposed. Although some hybrid improper ferroelectric materials with Ruddlesden-Popper structures have been discovered experimentally, the small polarizations and high coercive fields will severely limit their practical applications. To deal with this issue, an alternative way is proposed by the first-principles calculations in the present work. By calculating the energies of phases with oxygen octahedral rotation and tilting in Ca3TiMO7 (M = Si, Ge, Mn, Sn, Hf, and Zr) compounds with five B-site ordering configurations, it is found that the tolerance factor has a considerable impact on their ferroelectric properties. The energy barriers and ferroelectric polarizations increase with decreasing tolerance factor. Moreover, the individual-layer contributions to the total polarizations depend on the space group, which is also decided by the tolerance factor of the compound. Therefore, to enhance the ferroelectric polarization in B-site substituted Ca3Ti2O7, the tolerance factor should be decreased according to the calculation results of this work. [ABSTRACT FROM AUTHOR]

Published
2018
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40. The A-site driven phase transition procedure of (Pb0.97La0.02)(Zr0.42Sn0.40Ti0.18)O3 ceramics: An evidence from electronic structure variation.

Author

Chen, X., Jiang, P. P, Duan, Z. H., Hu, Z. G., Chen, X. F., Wang, G. S., Dong, X. L., and Chu, J. H.

Subjects
*PHASE transitions, *ELECTRONIC structure, *DIELECTRIC function, *ANTIFERROELECTRIC materials, *X-ray diffraction
Abstract

The transition of (Pb0.97La0.02)(Zr0.42Sn0.40Ti0.18)O3 (PLZST) ceramic has been investigated by temperature-dependent X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). The rhombohedral and tetragonal symmetries are confirmed by XRD analysis. Two interband transitions (Ecp1 and Ecp2) located at about 3.7 and 5.2 eV can be derived from the second derivative of the complex dielectric functions using the standard critical point (SCP) model. Except for the negative temperature coefficient parts, the transitions present additional parts corresponding to appearance of the antiferroelectric (AFE) phase. The phenomena can be attributed to variation of the electronic structure during A-site driven phase transition. [ABSTRACT FROM AUTHOR]

Published
2013
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42. Metamorphic InAs1-xBix/In0.83Al0.17As quantum well structures on InP for mid-infrared emission.

Author

Gu, Y., Zhang, Y. G., Chen, X. Y., Ma, Y. J., Xi, S. P., Du, B., Ji, W. Y., and Shi, Y. H.

Subjects
QUANTUM wells, ENERGY-band theory of solids, PHOTOLUMINESCENCE, BISMUTH compounds, METALS
Abstract

This work reports on InP-based metamorphic quantum well structures with bismuth incorporation for mid-infrared applications. InAs1-xBix quantum well structures have been grown on InP-based metamorphic In0.83Al0.17As buffers and photoluminescence beyond 3.1 µm has been achieved at 300K, which is longer than the referenced InAs quantum well. X-ray diffraction, cross-sectional transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements reveal clear interfaces of InAsBi quantum well with low bismuth, while more defects and bismuth inhomogeneity were observed as more bismuth was incorporated. [ABSTRACT FROM AUTHOR]

Published
2016
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