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Project titleDevelopment of scientific and technological basics of ion-beam synthesis of gallium oxide nanoinclusions for use in advanced electronic devices

Research area 09 - ENGINEERING SCIENCES, 09-703 - Promising technological processes in nano- and microelectronics

Keywordsion synthesys, gallium oxide, nanocrystals, thermal treatment, impurities, defects, luminescence, photoconductivity, DFT calculations

Annotation
This project is devoted to solving a scientific problem associated with the development of the physical basis for the synthesis and modification of nanostructures based on gallium oxide to create promising electronic and optoelectronic devices based on it. The relevance of the research claimed in this project is determined, on the one hand, by the unique properties of gallium oxide, and, on the other hand, by the unresolved number of problems that hinder its widespread use. Gallium oxide is a semiconductor with a large band gap (about 5 eV), which makes it relevant to use in power electronics (due to high breakdown voltages) and as photodetectors of ultraviolet radiation. At the same time, it attracted the attention of researchers and developers by such advantages as high thermal and chemical resistance, versatility, the ability to grow large-diameter wafers, and their relatively low cost compared to other wide-gap semiconductors (SiC, GaN). Despite its unique physical properties and the success achieved in the creation of both single crystals and thin layers of gallium oxide, this material has not yet found wide commercial use. One of the key disadvantages limiting its application is associated with a high concentration of growth defects and, especially, with insufficient controllability of the concentrations of point defects and impurities which determine the electronic and optical properties of this material. Due to the existing physical limitations, the equilibrium methods for the synthesis of gallium oxide do not yet make it possible to overcome these disadvantages. In this regard, the problem of using non-equilibrium methods and fundamentally new approaches to the synthesis of this material becomes urgent. As one of the promising methods for obtaining high-quality structures with controlled parameters in this project it is proposed for the first time to use ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices, which has been well developed for nanocrystals of such semiconductors as Si, SiC, GaN, ZnO, and others. The non-equilibrium character and high degree of purity of the ion implantation method are important for overcoming a number of physical and chemical limitations inherent in Ga2O3. The studies planned in this project combine the advantages of both the material used, gallium oxide, and the proposed approach, ion-beam synthesis of nanocrystals in a dielectric matrix. Their results will be of great practical importance for the creation of electronic and optoelectronic devices of a new generation, including those in integral design. Within the framework of the proposed project, for the first time, a systematic study of the regularities of ion-beam synthesis of nanoinclusions of gallium oxide in dielectric matrices will be carried out and their influence on the structure and properties of the studied materials will be established. Also, for the first time, a promising approach will be investigated for flexible control of the parameters of structures with Ga2O3 nanocrystals using additional ion doping with various impurities, as well as controlled control of defects by ion irradiation, which is especially important for the creation of light-emitting and photodetecting devices. It is expected that the new approach proposed in this project will make it possible to overcome the drawbacks of gallium oxide associated with the difficulty of reproducible preparation of nanostructures with a given impurity-defect composition while maintaining the structural parameters of the material, and thereby create the prerequisites for wide practical application of structures with Ga2O3 nanocrystals in modern electronics and optoelectronics devices.

Expected results
The main result of the project will be the development of a new method for creating nanomaterials based on gallium oxide by ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices for use in promising nano- and optoelectronic devices. Also, within the framework of the project, the following results will be obtained. Various variants of scientific and technological solutions will be proposed for the ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices with variations in the order of implantation, ion energy and dose, as well as conditions for post-implantation annealing. Preliminary experiments on high-dose implantation of Ga+ and O+ ions into dielectric matrices with subsequent annealing will be carried out, as a result of which test structures with Ga2O3 nanoinclusions will be synthesized and their structural, optical and luminescent properties will be investigated. Electronic and hole spectra of "pure" Ga2O3 nanocrystals of various structural modifications, depending on their geometric dimensions, will be obtained. Based on the results of the studies carried out at the first stage, the technological regimes of ion-beam synthesis (the order of implantation, ion energy and dose, temperature, time and atmosphere of annealing) will be refined in order to improve the structural quality and luminescent properties of structures with gallium oxide nanocrystals. Based on the refinement results, optimized versions of the structures will be fabricated and their structure, optical and luminescent properties will be studied. The regularities of the effect of additional ion doping (with variation of the parameters of additional ion irradiation and post-radiation annealing) on the structure and luminescent properties of gallium oxide nanocrystals will be established. Electronic and hole spectra of Ga2O3 nanocrystals of various structural modifications will be obtained, depending on the type of dopant, the degree of doping, and the geometric dimensions of the crystallites. The regularities of the influence of the defects introduction on the structure and luminescence properties of gallium oxide nanocrystals under irradiation with ions of both chemically active and inactive elements will be established. The parameters of light emission and photoresponse (rates of radiative recombination, quantum efficiency of photoabsorption processes) in heterophase systems with Ga2O3 nanocrystals will be calculated. A technological process for the fabrication of laboratory samples of photosensitive structures will be developed, which includes the operations of photolithography and the deposition of contacts. Laboratory samples will be made and the spectral characteristics of photoconductivity will be studied. The main regularities of ion synthesis and ion-beam modification of the properties of Ga2O3 nanocrystals in dielectric matrices will be analyzed and proposals for the practical use of the project results will be developed. The expected results will correspond to the world level of research, as evidenced by their publication through the publication of at least 8 articles in high-impact journals on the subject of the project, including such journals as Applied Physics Letters, Nanotechnology, Journal of Luminescence, Journal of Applied Physics, IEEE Sensors , Nuclear Instruments and Methods in Physics Research B. At least 7 reports will be presented at representative international and all-Russian conferences. The practical significance of the project results lies in obtaining information on the light-emitting and photoconductive properties of structures based on Ga2O3 nanocrystals in dielectric matrices, which can underlie the creation of effective devices of a new generation: "solar-blind" UV detectors, light-emitting devices and devices that convert UV-radiation in the visible range. The research results seem promising in light of the accelerating pace of development of technologies using UV radiation in electronics, optics, chemistry, medicine and biology.

Annotation of the results obtained in 2021
At the first stage of the project implementation, the following works were performed. Various variants of scientific and technological solutions for ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices have been developed. The proposed variants differ in the use of various initial dielectric matrices (SiO2/Si and Al2O3/Si films, as well as fused quartz and sapphire), ion implantation conditions (the dose of implanted ions, as well as the order of implantation) and post-implantation annealing (variation of temperature, time and atmosphere). Some of the developed scientific and technological solutions for the ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices were implemented during preliminary experiments on high-dose implantation of Ga+ and O+ ions into dielectric matrices followed by annealing. Experimental samples were fabricated with a variation in the order of irradiation with gallium and oxygen ions, as well as with irradiation with only gallium ions. The irradiated samples were subjected to successive annealing at temperatures of 300-900 °C. The study of the properties of the synthesized materials was carried out using a large number of experimental techniques, including X-ray photoelectron spectroscopy with depth profiling, Raman spectroscopy, optical transmission, photoluminescence spectroscopy, X-ray diffraction, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. A theoretical calculation of the electronic states in Ga2O3 nanocrystals of various modifications was carried out with a variation in their geometric parameters. The electron and hole spectra were calculated for spherical (quasi-spherical) Ga2O3 nanocrystals placed in wide-gap dielectric matrices of silicon dioxide SiO2 and aluminum oxide Al2O3 using the envelope function approximation. The following scientific results have been obtained. Various variants of scientific and technological solutions for the ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices with a variation in the order of implantation, energy and dose of ions, as well as post-implantation annealing conditions are proposed. Based on a computer calculation of the distribution profiles of implanted atoms, as well as on the basis of known data on the patterns of ion-beam synthesis, several variants are proposed that differ in the material of the initial dielectric matrix, the order of implantation of ions, the concentration of implanted atoms, and the conditions of post-implantation annealing. Preliminary experiments on high-dose implantation of Ga+ and O+ ions into dielectric matrices followed by annealing were carried out, as a result of which test variants of structures with Ga2O3 nanoinclusions were synthesized. The study of the composition of implanted samples revealed the formation of Ga-O bonds even in the absence of annealing for all variants of structures based on SiO2/Si films, and for Al2O3/Si structures additionally irradiated with oxygen ions. Using the Raman scattering method, the appearance of new peaks for some variants of the synthesized structures after annealing at 500 and 700 °C was established, which can presumably be associated with the formation of gallium oxide nanocrystals of the gamma phase. X-ray diffraction for samples after annealing at 900 °C revealed the appearance of a weak peak, presumably related to the β-phase. As a result of annealing, a line appears in the photoluminescence spectra with a maximum in the region of 450-500 nm, presumably associated with the recombination of donor-acceptor pairs in gallium oxide. A shift of the maximum of the luminescence line with an increase in the annealing temperature was found, which is associated with a change in the size of nanoinclusions. The formation of β-Ga2O3 nanocrystals for SiO2/Si samples irradiated with gallium and oxygen after annealing at 900 °C was confirmed by transmission electron microscopy (taking into account the data of analysis by secondary ion mass spectroscopy). The electronic states in Ga2O3 nanocrystals of various modifications are calculated for varying their geometric dimensions. The positions of the energy levels are determined and the influence of size quantization of electrons on the position of the levels is established. All tasks set at the reporting stage of the project were completed. The results obtained make an important contribution to achieving the project goal and create a groundwork for creating a new class of materials based on gallium oxide. Project page at ResearchGate https://www.researchgate.net/project/Development-of-scientific-and-technological-basics-of-ion-beam-synthesis-of-gallium-oxide-nanoinclusions-for-use-in-advanced-electronic-devices

Publications

1. Korolev D., Nikolskaya A.,Mullagaliev T., Nezhdanov A., Belov A., Mikhaylov A., Kryukov R., Kumar M., Almaev A., Tetelbaum D. Ion implantation technology for the synthesis and modification of gallium oxide Proceedings of the IX International Scientific Conference «Actual problems of solid state physics» (APSSP-2021), Minsk, Belarus, November 22-26, 2021., с.135 (year - 2021)

2. Korolev D.S., Nikolskaia A.A., Matyunina K.S., Mikhaylov A.N., Belov A.I., Nezhdanov A.V., Kriukov R.N., Zdoroveyshchev A.V., Konakov A.A., Tetelbaum D.I. Ионно-лучевой синтез нанокристаллов оксида галлия в диэлектрических матрицах XXVI Международный Симпозиум «Нанофизика и наноэлектроника». Труды симпозиума, Н. Новгород, 14-17 марта, 2022., Т.2. – С.852-853 (year - 2022)

3. - 12 проектов молодых учёных ННГУ поддержаны грантами РНФ Официальный сайт Университета Лобачевского, Новости университета от 06.07.2021 (year - )

Annotation of the results obtained in 2022
At the second stage of the project implementation, the following works were performed. The development of our proposed approach for obtaining nanomaterials based on gallium oxide by ion synthesis of Ga2O3 nanocrystals (NC) in dielectric matrices continued at this stage of research, taking into account the results obtained at the first stage of research. The technological regimes of ion-beam synthesis have been refined in order to improve the structural perfection and luminescent properties of structures with gallium oxide nanocrystals. The set of options for ion-beam synthesis was corrected, the main changes concerned the variation in the dose of oxygen ions incorporation to obtain the stoichiometric concentration of Ga2O3 and changing the conditions of post-implantation heat treatment. Experimental samples were made taking into account the refinements of the technological modes of ion synthesis. The study of the properties of the synthesized samples was carried out using a large number of experimental techniques, including X-ray photoelectron spectroscopy with depth profiling, optical transmission, photoluminescence spectroscopy, X-ray diffraction, transmission electron microscopy, including high resolution. A study was made of the properties of structures with ion-synthesized nanocrystals of gallium oxide, in which ions of elements that exhibit doping properties for gallium oxide (silicon) will be additionally implanted, followed by annealing to activate them. The proposed variants differed in the order of ion implantation: before or after heat treatment of the samples implanted with gallium and oxygen ions, as well as before and after the final annealing. Theoretical calculations were made of the electronic states in Ga2O3 nanocrystals with various dopants depending on the crystallite size. Donors of the fourth group were chosen as impurities. The calculation was carried out in the approximation of the envelope function method. The donor potential was taken into account according to the perturbation theory in the Rayleigh-Ritz variational method. The following scientific results have been obtained. Taking into account the results of the first stage of research, experiments were carried out to refine the technological regimes of ion-beam synthesis (implantation order, energy and dose of ions, temperature, duration and atmosphere of annealing) in order to improve the structural quality and luminescence properties of structures with gallium oxide nanocrystals. As part of a possible refinement of the technological regimes of ion synthesis, experiments were carried out to study the chemical composition of implanted samples after post-implantation annealing and a comparison of the obtained data with data on the composition of samples without annealing, obtained at the first stage of the project. Analysis of the composition by X-ray photoelectron spectroscopy demonstrated the effectiveness of refined technological solutions: for one of the variants of ion synthesis, annealing in an oxygen atmosphere led to an increase in the fraction of gallium in the stoichiometric oxide state above 90 at.%. A study of the structure by high-resolution transmission electron microscopy has shown that these conditions of ion-beam synthesis ensure the formation of γ- and β-Ga2O3 nanocrystals with an average size of 4–9 nm. Regularities of the effect of additional ion doping on the properties of gallium oxide nanocrystals were studied using for doping with silicon atoms introduced by ion implantation. For some variants of ion synthesis used, an increase in luminescence intensity was demonstrated, and a shift in the optical absorption edge was found, indicating a change in the energy structure of nanocrystals. The electron and hole spectra of Ga2O3 nanocrystals containing a dopant are calculated for various geometric sizes of crystallites. It is shown that in doped nanocrystals the electron energy increases with the NC radius and tends to the energy level of an electron localized on a donor in a bulk material. For holes, the effect of the donor decreases with an increase in the nanocrystal size, and in the limit, the donor will have a negligibly weak effect on the hole states, which takes place in a bulk material. All tasks set at the reporting stage of the project were completed. The results obtained make an important contribution to achieving the project goal and create a groundwork for creating a new class of materials based on gallium oxide.

Publications

1. Korolev D.S., Kriukov R.N., Matyunina K.S., Nikolskaya A.A., Belov A.I., Mikhaylov A.N., Sushkov A.A., Pavlov D.A., Tetelbaum D.I. Structure and chemical composition of ion-synthesized gallium oxide nanocrystals in dielectric matrices Nanomaterials, - (year - 2023)

2. Korolev D.S., Matyunina K.S., Nikolskaya A.A., Kriukov R.N., Nezhdanov A.V., Belov A.I., Mikhaylov A.N., Sushkov A.A., Pavlov D.A., Yunin P.A., Drozdov M.N., Tetelbaum D.I. Ion-Beam Synthesis of Gallium Oxide Nanocrystals in a SiO2/Si Dielectric Matrix Nanomaterials, Vol.12., P.1840 (year - 2022) https://doi.org/10.3390/nano12111840

3. Korolev D.S., Matyunina K.S., Nikolskaya A.A., Belov A.I., Mikhaylov A.N., Nezhdanov A.V., Kriukov R.N., Sushkov A.A., Pavlov D.A., Yunin P.A., Drozdov M.N., Tetelbaum D.I. Ионный синтез наноразмерных включений Ga2O3 в диэлектрических матрицах Труды XXVII Международного симпозиума "НАНОФИЗИКА И НАНОЭЛЕКТРОНИКА" (13-16 марта 2023 г., Нижний Новгород), т.2, стр.633-634 (year - 2023)

4. Korolev D.S., Matyunina K.S., Nikolskaya A.A., Nezhdanov A.V., Mikhaylov A.N., Belov A.I., Kriukov R.N., Yunin P.A., Drozdov M.N., Sushkov A.A., Pavlov D.A., Tetelbaum D.I. Ионный синтез нанокристаллических включений Ga2O3 в оксидных матрицах VIII Всероссийская конференция и школа молодых ученых и специалистов «Физические и Физико-Химические Основы Ионной Имплантации» (ФФХОИИ-2022). Тезисы докладов, Казань, 11-14 октября, 2022., с.25 (year - 2022)

5. Korolev D.S., Nikolskaya A.A., Matyunina K.S., Mikhaylov A.N., Belov A.I., Nezhdanov A.V., Kriukov R.N., Sushkov A.A., Pavlov D.A., Yunin P.A., Tetelbaum D.I. Исследование процессов ионно-лучевого формирования нановключений оксида галлия в диэлектрических матрицах XV Российская конференция по физике полупроводников. Тезисы докладов, Нижний Новгород, 03-07 октября, 2022, С.71 (year - 2022)

6. Korolev D.S., Nikolskaya A.A., Matyunina K.S., Mikhaylov A.N., Belov A.I., Nezhdanov A.V., Kriukov R.N., Tetelbaum D.I. Ионно-лучевое формирование нановключений Ga2O3 51-ая Международная Тулиновская конференция по физике взаимодействия заряженных частиц с кристаллами (ФВЗЧК-2022). Тезисы докладов, Москва, 24 - 26 мая, 2022., С.115 (year - 2022)

7. Kriukov R.N., Zubkov S.Yu., Nikolichev D.E., Korolev D.S.,Nikolskaya A.A.,Zdoroveyshchev A.V., Vasiliev V.K. Efficiency of GaOx nanoclusters formation in SiO2 and Al2O3 dielectric layers subjected to O+ and Ga+ ion implantation 9th International School and Conference on Optoelectronics, Photonics, Engineering and Nanostructures. Book of abstracts. Saint Petersburg, May, 24-27, 2022, С.482-483 (year - 2022)

8. Revin A.A., Chekusheva S.S., Konakov A.A., Korolev D.S. Электронный транспорт и размерное квантование в структурах на основе моноклинного оксида галлия VIII Всероссийская конференция и школа молодых ученых и специалистов «Физические и Физико-Химические Основы Ионной Имплантации» (ФФХОИИ-2022). Тезисы докладов, Казань, 11-14 октября, 2022., с.26 (year - 2022)