Type: European Regional Development Fund

Agreement No: 1.1.1.1/20/A/057

Duration: 01.01.2021 - 30.06.2023.

Project Leader: Institute of Solid State Physics University of Latvia (ISSP UL), Dr.hab.phys. Juris Purans

Project partners: SIA AGL Technologies, Dr.pys. Andis Azens, SIA BC Corporation Limited Dr.phys. Lauris Dimitrocenko.

Total budget: 537 004 EUR

ISSP UL budget: 322 000 EUR

Project description:

Gallium oxide Ga2O3 has become one of the most investigated materials of today. Nearly every issue of material-related scientific journals contains articles on growth, material properties, or device applications of gallium oxide. The reason for this large interest is the extremely promising properties for electronic and optical applications of this wide bandgap material, together with the relatively un-expensive substrate wafers. Very recently, ultrawide-bandgap spinel zinc gallate ZnGa2O4 has been demonstrated to exhibit several benefits over gallium oxide that merits to be investigated more deeply.

The aim of this industrial research project is to develop advanced high rate PVD magnetron sputtering and MOCVD technologies for deposition of functional ultrawide-bandgap gallium oxide Ga2O3 and zinc gallate ZnGa2O4 thin films for optoelectronics and electronics applications.

The main goals are:

  • To develop high rate PVD magnetron sputtering technology for deposition of pure and doped (p-type dopants and RE) amorphous and crystalline gallium oxide Ga2O3 thin films and ZnGa2O4 thin films. The applications in focus are (1) deep UV TCOs/TSOs and (2) efficient inorganic luminescence devices (a-Ga2Ox:RE).
  • To develop MOCVD technology of Ga2O3 and ZnGa2O4 thin films deposition and to establish epitaxial n- and p-type Ga2O3 and ZnGa2O4 thin film growth processes for deep UV optoelectronics and electronics applications.

The proposed Industrial research project will be implemented by ISSP LU, SIA AGL Technologies and SIA BC Corporation Limited. This Interdisciplinary Project consists of the research activities in Physical and Chemical sciences (1.3, 1.4) and Materials engineering (2.5).

 
 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.04.2022.- 30.06.2022.)

30.06.2022

The development of the high-speed deposition technology of ZnGa2O4 thin films was continued, by simultaneously sputtering a liquid gallium target and a zinc target in reactive DC mode. The process parameters were varied to develop the technology for obtaining highly transparent films with different Zn:Ga ratios and different degrees of crystallinity. The obtained layer manufacturing speed significantly exceeds the speeds obtained in the literature and also in this project, when the layers are manufactured in the RF mode. Tuning of the film production process was also continued by sputtering the ZnGa2O4 target in the RF mode. Preparation of a publication on the preparation and properties of Ga2O3 films was completed. (Activity 1).

Experimental work was initiated to find out the growth parameters of ZnGa2O4 for the existing MOCVD facility. Several experiments were conducted to determine the ratio of Zn and Ga precursors, and several experiments were conducted to determine the growth temperature of the ZnGa2O4 thin film. (Activity 2).

Characterization of the ZnGaxO4 films produced under different conditions was performed using optical spectroscopy, X-ray diffraction, ellipsometry, X-ray photoelectron spectroscopy, optical microscopy and Raman spectroscopy. Data collection was carried out, the results were used as feedback for adjusting the production process in Activity 1. Atomic force microscopy (AFM) measurements of Ga2O3 thin films were performed during the mission in the equipment available at the University of Tartu. AFM measurements were necessary to understand the surface morphology of the resulting thin films and to adjust their deposition parameters to obtain the smoothest possible surface. (Activity 4).


ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2022.- 31.03.2022.)

04.04.2022.

The production of Ga2O3 thin films was continued, sputtering the liquid gallium target in the reactive DC mode and the Ga2O3 target in the RF mode. It was found that in order to ensure the necessary stoichiometry of the films, the sputtering of the Ga2O3 target must also be performed in a reactive process. The development of a high-speed deposition technology for ZnGa2O4 thin films was initiated, simultaneously sputtering the liquid gallium target and the zinc target in the reactive DC mode. A set of process parameters for the production of highly transparent films was found. The production of films by sputtering the ZnGa2O4 target in RF mode was also started (Activity 1). A patent application with no. LVP2021000105 for A method for reactive magnetron sputter deposition of gallium oxide thin films has been submitted. (Activity 1)

The optimization of the growth of Ga2O3 thin films in the MOCVD plant was continued. The process for obtaining a high-temperature buffer layer was continued in order to obtain a higher degree of crystallization of Ga2O3 thin films. The growth of Ga2O3 and ZnGa2O4 thin films with MOCVD on sapphire substrates of different orientations was continued and the sputtering of Ga2O3 and ZnGa2O4 thin films on c-plane sapphire substrates was continued. Ga2O3 and ZnGa2O4 thin films were grown with PLD on sapphire substrates of different orientations and in-depth study of the structure and morphology of the grown thin films was performed. (Activity 2)

Ab-initio DFT calculations were performed for ZnO2 materials. DFT functionals and basis sets of Gaussian type functions within the linear combination of atomic orbitals (LCAO) approximation were examined and these results were compared with the experimental data and planewave calculations. According to the performed calculations and the obtained results, the scientific article "Zinc peroxide from the first principles" has been prepared. (Activity 3)

Characterization of Ga2O3 and ZnGa2O4 films prepared under different conditions was performed by optical spectroscopy, X-ray diffraction and Raman spectroscopy. High-resolution X-ray diffraction analysis (performed in collaboration with partners from Angström Laboratory, Uppsala, Sweden) showed that the high-temperature Ga2O3 films on the sapphire substrate are epitaxial. Analysis of the composition of Ga2O3 films by ERDA (in collaboration with KTH, Stockholm, Sweden) and XPS showed that the films are free of impurities. The morphology of the films was analysed by electron microscopy (Activity 4).

A publication on the preparation and properties of Ga2O3 films was started.

In-depth high-resolution X-ray diffraction measurements of crystalline Ga2O3 thin films were initiated to determine their degree of monocrystallinity and epitaxial orientation to sapphire substrates. (Activity 4)


ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.10.2021. - 31.12.2021.)

11.01.2022.

The development of high-speed application technology of Ga2O3 thin films was continued, and the parameters of the sample preparation process were optimized by sputtering the liquid gallium target in the reactive direct current mode. A series of amorphous and crystalline samples were prepared on quartz and sapphire substrates in the temperature range from room temperature to 800oC. Ga2O3 thin films were created by sputtering the Ga2O3 target in RF mode. A LV patent application for Ga2O3 thin film deposition technology for sputtering a liquid gallium target in reactive direct current mode was prepared and filed. (Activity 1)

The growth of Ga2O3 thin films in the MOCVD plant is further optimized by simultaneously combining H2O and O2 precursor gases. In order to obtain a higher degree of crystallization, a process for obtaining a high-temperature buffer layer is being developed. An in-depth study of the structure and morphology of the grown thin films is being carried out. (Activity 2)

Ab-initio DFT calculations were employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga2O3 crystals. Hybrid exchange–correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga2O3. The calculations predict that an oxygen vacancy in β-Ga2O3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga2O3. All types of charge states of gallium vacancies are sufficiently deep acceptors, however, due to high formation energy, they cannot be considered as a source of p-type conductivity in β-Ga2O3. As a result, a scientific publication " Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure" was prepared and published in Materials. (Activity 3)

Optical transmittance, reflection and absorption spectra, X-ray diffraction and Raman spectroscopy data of Ga2O3 coatings prepared under different conditions were studied and collected. (Activity 4)

Publication:

Usseinov, Abay; Koishybayeva, Zhanymgul; Platonenko, Alexander; Pankratov, Vladimir; Suchikova, Yana; Akilbekov, Abdirash; Zdorovets, Maxim; Purans, Juris; Popov, Anatoli. Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure. Materials. 14, 7384 (2021); DOI:10.3390/ma14237384

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.07.2021. - 30.09.2021.)

11.10.2021.

Within the framework of the project, the development of high-speed Ga2O3 thin films deposition technology has been started and the production and characterization of a series of samples has been performed. The optical transmittance, reflection and absorption spectra, X-ray diffraction data and properties of Ga2O3 coating at different temperatures were studied and collected. (Activity 1).

A price survey was conducted and the purchase of sputtering targets was made (Activity 1).

The preparation of the Aixtron (AIX-200RF) MOCVD system for the growth of Ga2O3 and ZnGa2O4 films was completed and the preparation of the technical report has been started. Work has begun on growing Ga2O3 thin films on c-plane sapphire using H2O as the oxygen source. The development and drawing of a new reactor design is continued in cooperation with SIA BC Corporation Limited - the drawing of the chamber's cooling body, substrate heater and rotation mechanism is being performed. The MOCVD is now equipped with an O2 gas precursor, which is used in parallel with H2O for Ga2O3 thin film synthesis experiments. An in-depth study of the structure and composition of the grown thin films is performed. (Activity 2).

Nanocrystalline zinc peroxide (nano-ZnO2) was synthesized through a hydrothermal process and comprehensively studied using several experimental techniques. Its crystal structure was characterized by X-ray diffraction. The temperature-dependent local environment around zinc atoms was reconstructed using reverse Monte Carlo (RMC) analysis. Lattice dynamics of nano-ZnO2 was studied by infrared and Raman spectroscopy. The obtained experimental results were supported by first-principles density functional theory (DFT) calculations. As result scientific publication "A comprehensive study of structure and properties of nanocrystalline zinc peroxide" was prepared and published in Journal of Physics and Chemistry of Solids. (Activity 3).

The preparation and testing of structural and morphological methods (XRD, XPS, SEM, TEM) for the characterization of Ga2O3 and ZnGa2O4 thin films were completed and the preparation of a technical report has been started. The characterization of Ga2O3 thin films obtained by magnetron sputtering and MOCVD was started in order to understand and optimize deposition processes. (Activity 4).

The project results were presented at the 2021 Fall Meeting conference of the European Materials Research Society (E-MRS) with a poster presentation "Growth of gallium oxide based core-shell nanowire heterostructures". (Activity 4).

Publication:

A comprehensive study of structure and properties of nanocrystalline zinc peroxide
Bocharov D., Chesnokov A., Chikvaidze G., Gabrusenoks J., Ignatans R., Kalendarev R., Krack M., Kundzins K., Kuzmin A., Mironova-Ulmane N., Pudza I., Puust L., Sildos I., Vasil'chenko E., Zubkins M., Purans J.
Journal of Physics and Chemistry of Solids, Volume 160, January 2022, 110318
DOI: https://doi.org/10.1016/j.jpcs.2021.110318 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.04.2021.-30.06.2021.)

23.07.2021.

Preparation of the sputtering system for use in two-magnetron DC, RF and HiPIMS sputtering configuration was continued. The design and installation of target containers for metallic Ga targets suitable for reactive sputtering from a liquid metal target and arrangement of the chamber interior geometry for sputtering in upward direction was completed. Testing of the installed target has been started. Practical knowledge related to the growth of Ga2O3 and ZnGa2O4 thin films on their structure, electrical and optical physical properties has been acquired. As a result of the research, a scientific article “A comprehensive study of the structure and properties of nanocrystalline zinc peroxide” was prepared and submitted (activity 1).

Plasma Optical Emission spectroscopy line has been installed and tuned, Gallium spectral lines have been identified for process control (activity 1).

Aixtron (AIX-200RF) MOCVD system preparation for Ga2O3 and ZnGa2O4 thin film deposition has been performed: fabrication and testing of a new silicon carbide heating element in an oxidative atmosphere; growing Ga2O3 and ZnGa2O4  thin films with MOCVD on sapphire substrates of different orientations; engineering and drawing of a new reactor design in collaboration with SIA BC Corporation Limited (activity 2).

Ab-initio calculations of doped Ga2O3 was conducted. Analysis of material atoms, electronic and oscillation properties, analysis of formation energies of various configurations were performed. The article “Ab-initio calculations of oxygen vacancy in Ga2O3 crystals” was published in an internationally cited journal: LATVIAN JOURNAL OF PHYSICS AND TECHNICAL SCIENCES, Vol. 58, N 2 (2021), 3-11 (activity 3).

An open procurement was announced for the purchase of substrates, chemicals and other laboratory equipment necessary for the implementation of the project. Preparation and testing of structural and morphology characterization methods (XRD, XPS, SEM, TEM) for Ga2O3 and ZnGa2O4 thin films has been continued (activity 4).

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2021. - 31.03.2021.)

02.04.2021.

As part of Project No 1.1.1.1/20/A/057 preparation and testing of the vacuum system, gas inlet system, substrate heating system, target cooling and heating system and connection of the necessary (DC, RF, HiPIMS) power supplies for use in two-magnetron sputtering configuration has been started. Development of design of target containers for metallic Ga targets suitable for reactive sputtering from a liquid metal target and arrangement of the chamber interior geometry for sputtering in upward direction also is started (activity 1).

Magnetron sputtering targets purchase order placed (activity 1).

Aixtron (AIX-200RF) MOCVD system preparation for Ga2O3 and ZnGa2O4 thin film deposition has been done: testing of reactor stability at high temperature while using oxidative precursor; engineering and drawing of a new reactor design in collaboration with SIA BC Corporation Limited; replacement of malfunctioning parts (activity 2).

Study was conducted and the formation energy and transition levels of oxygen vacan­cies in β-Ga2O3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach was calculated. As result information for article “Ab-initio calculations of oxygen vacancy in Ga2O3 crystals” was prepared (activity 3).

Preparation and testing of structural and morphology characterization methods (XRD, XPS, SEM, TEM) for Ga2O3 and ZnGa2O4 thin films has been done (activity 4).