Defekty punktowe w amonotermalnym azotku galu

Nitride semiconductors (GaN, AlN, InN) and their AlInGaN alloys are known for applications in power and high frequency electronics as well as optoelectronics (white LED light sources, blue, and green semiconductor lasers). Most devices are currently deposited in the process of epitaxy of thin nitride-based quantum structures on foreign substrates, such as sapphire, SiC, or Si. This significantly reduces the quality and performance of the devices because of lattice constant and thermal expansion coefficient mismatch between the device structure and the substrate. However, there is a growing interest in replacing the foreign substrates with bulk GaN ones. This is especially important in the case of high-power electronic components, which require high operating voltages, and lasers with high optical power. The technology to obtain bulk GaN substrates is difficult and their availability on the market is limited. 

Poland is one of the leaders in the fabrication of high quality GaN crystals and substrates. Ammonothermal (AT) and Halide Vapor Phase Epitaxy (HVPE) growth technologies are developed at the Institute of High Pressure Physics PAS (IHPP PAS). Main effort will be dedicated to GaN crystals obtained by ammonothermal method (AT-GaN). AT crystallization consists of dissolution of GaN feedstock in supercritical ammonia in one zone of a high-pressure autoclave and its convection-driven transport to the second zone where solution is supersaturated and crystallization of GaN on native GaN seeds takes place. The process is performed at temperature of 450-550°C and ammonia pressure of the order of a few kbars. The method allows to obtain crystals of extremely low threading dislocation density and small bending of crystallographic planes. One of disadvantages of the ammonothermal method is the low purity of the obtained crystals, i.e., a relatively high concentration of point defects (foreign atoms of dopants and structural point defects). HVPE method allows for a fast growth of thick crystals at temperature above 1000°C. Unlike AT- GaN, HVPE-GaN is characterized by high purity, meaning much lower concentration of donor dopants and compensating defects. HVPE-GaN crystals will be used as reference in order to create a more general picture of point defects in bulk GaN. 

The main unintentional dopant in the AT-GaN crystals is oxygen, which acts as a donor and is the reason of n-type (electron) conductivity. In order to achieve a hole conductivity (p-type), intentional doping with acceptors, such as Mg or Zn, of a sufficiently high concentration is applied. It is also possible to obtain crystals of high resistivity at room temperature (> 106 Ω cm) if the oxygen donors are perfectly compensated by shallow (Mg, Zn) or deep (Mn) acceptors. Preliminary studies indicate that the main defects present in AT- GaN are gallium vacancies, which can additionally bind a maximum of four hydrogen atoms. Such defects may limit the fabrication of crystals with the desired electrical properties, form absorption bands in the visible range or actively participate in optical transitions, e.g., constituting as non-radiation recombination centers.

The project opens an opportunity of studying defect physics in GaN of a wide spectrum of electrical properties (type n, type p, high resistance crystals) and doping level. It will provide a lot of valuable information about the favored conditions of point defect formation, verification of energy level positions known from theoretical calculations, as well as interaction with impurities. It can shed new light on the behavior of defects during post-growth annealing of AT-GaN crystals with a significant concentration of oxygen and gallium vacancies. Especially in AT-GaN doped with acceptors the role of oxygen, hydrogen, Ga vacancies complexed with hydrogen is not well established and dehydrogenation process is not well understood. Thus, an explanation of microscopic change of the defect distribution and resulting resistivity of AT-GaN after thermal annealing will be a measurable success of the project. Knowledge about the type and concentration of point defects in bulk GaN crystals is essential for controlling their purity as well as electrical properties of substrates prepared for specific applications.

Project Goal

The main goals of the project are:

1. identification of point defects in bulk AT-GaN crystals of various
   conductivity 
2. impact of the defect concentration on the electrical and optical properties of bulk GaN
3. determination of the microscopic mechanism of change of electrical properties after annealing. A complex analysis and determination of concentration of point defects in AT-GaN will be carried out using various experimental methods. The experimental results will be described using calculations based on the charge neutrality equation to obtain a comprehensive image of point defects in bulk AT-GaN.

International Collaboration

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Publications

Project results have been published in:

• M. A. Reshchikov, M. Vorobiov, K. Grabiańska, M. Zajac, M. Iwinska, M. Bockowski, Journal of Applied Physics, “Defect-related photoluminescence from ammono GaN”, 129 (2021) 095703, https://doi.org/10.1063/5.0045019.
• M. Reshchikov, D. Demchenko, D. Ye, O. Andrieiev, M. Vorobiov, K. Grabianska, M. Zajac, P. Nita, M. Iwinska, M. Bockowski, „The effect of annealing on photoluminescence from defects in ammonothermal GaN” Journal of Applied Physics 131 (2022) 035704, https://doi.org/10.1063/5.0077796.
• M. Amilusik, M. Zajac, T. Sochacki, B. Łucznik, M. Fijalkowski, M. Iwinska, D. Włodarczyk, A.K. Somakumar, A. Suchocki, M. Bockowski, “Carbon and Manganese in Semi-Insulating Bulk GaN Crystals”, Materials 15(7) (2022) 2379, https://doi.org/10.3390/ma15072379.
• L. Konczewicz, E. Litwin-Staszewska, M. Zajac, H. Turski, M. Bockowski, D. Schiavon, M. Chlipała, Malgorzata Iwinska, P Nita, S. Juillaguet, S. Contreras, “Electrical transport properties of highly doped N-type GaN materials”, Semiconductor Science and Technology 37 (2022) 055012, DOI: https://10.1088/1361-6641/ac5e....
• L.Konczewicz, M. Iwinska, E. Litwin-Staszewska, M. Zajac, H. Turski, M. Bockowski, D. Schiavon, M. Chlipała, S. Juillaguet, S. Contreras, “Negative Magnetoresistivity in Highly Doped n-Type GaN”, Materials 15(20) (2022) 7069, https://doi.org/10.3390/ma15207069.
• Q. Liu, M. Zajac, M.Iwińska, S. Wang, W. Zhuang, M. Bockowski, X. Wang, “Carbon doped semi-insulating freestanding GaN crystals by ethylene”, Applied Physics Letters 121 (2022) 172103, https://doi.org/10.1063/5.0118250.
• L. Konczewicz, S. Juillaguet, M. Zajac, E. Liwin-Staszewska, M. Al. Khalfioui, M. Leroux, B. Damilano, J. Brault, S. Contreras, “Low-Temperature Electrical Transport Properties of Molecular Beam Epitaxy-Grown Mg-Doped GaN” Subjected to a High-Temperature Annealing Process, Phys. Status Solidi A, 22, 2200769 (22.01.2023), https://doi.org/10.1002/pssa.202200769.
• M. Amilusik, M. Zajac, M. Fijalkowski, M. Iwinska, T. Sochacki, D. Wlodarczyk, A.K. Somakumar, R. Jakiela, A. Suchocki, M. Bockowski, “Role of carbon in n-type bulk GaN crystals”, Journal of Crystal growth 632 (2024) 127641, https://doi.org/10.1016/j.jcrysgro.2024.127641.
• M. Zajac, P. Kaminski, R. Kozlowski, E. Litwin-Staszewska, R. Piotrzkowski, K. Grabianska, R. Kucharski R. Jakiela, „Formation of Grown-In Nitrogen Vacancies and Interstitials in Highly Mg-Doped Ammonothermal GaN”, MDPI Materials 17 (2024) 1160, https://doi.org/10.3390/ma17051160.

Submitted patents

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Professor

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PhD Theses

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Master theses

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Lectures

Project results have been presented by:

• M. Bockowski, „Recent progress in bulk GaN crystal growth” Materials Science and Advanced Electronics Created by Singularity (on-line international conference organized by Tokyo University); 01-03.02.2021 (invited talk).
  
• M. Bockowski, Huawei Strategy and Technology Workshop (STW) 2021, 14-16.10 2021, „GaN-on-GaN technology - challenges and perspectives” (international on-line conference organized by Huawei Corporation), invited talk.
  
• M. Bockowski, “Towards GaN-on-GaN high-power electronic devices”, IGIR Open Seminar at Institute of Global Innovation Research, Tokyo University of Agriculture and Technology, Tokyo, Japan, 20.12. 2022 (invited talk).
  
• M. Bockowski, “Towards GaN-on-GaN” high-power electronic devices, 2022 European Innovation Stars Workshop, 18.11. 2022 Leuven, Belgium; (invited talk).
  
• M. Bockowski, “Towards GaN-on-GaN high-power electronic devices”, Swedish Centre for III-nitride technology (C3NiT), Linkoping, Sweden, 10.11. 2022; (invited talk).
  
• K. Grabianska, R. Kucharski, T. Sochacki, M. Bockowski, “On stress induced polarization effect in ammonothermally-grown GaN crystals” , 9th International Conference on Light -Emitting Devices and Their Industrial Applications, LEDIA-2022, Pacifico-Yokohama, Japan&on-line, 21-22.04 (2022), hybrid mode (on-line participation), invited talk.
  
• M. Bockowski, “What has recently been discovered and what we still need to find out about crystallization of truly bulk GaN”, The International Workshop on Nitride Semiconductors (IWN), 09-14.10, 2022 Berlin, Germany; (invited talk).
  
• M. Zajac, L. Kończewicz, E. Litwin Staszewska, R. Piotrzkowski, M. Boćkowski, Roman Kozłowski, Paweł Kamiński, “Point defects in ammonothermal GaN”, Institute of High Pressure Physics PAS Seminar on Nitride Semiconductors, 06.02.2023, Warsaw, Poland (invited lecture on seminar presented in hybrid mode).
  
• M. Zając, L. Kończewicz, E. Litwin Staszewska, R. Piotrzkowski, Roman Kozłowski, Paweł Kamiński, “Role of Nitrogen Vacancies in Obtaining Semi-Insulating Properties of Ammonothermal GaN:Mg”, 32nd International Conference on Defects in Semiconductors, 10-15.09.2023 Rehoboth Beach, USA, Delaware (contributed talk).

Posters

• M. Zajac, P. Nita, L. Konczewicz, R. Piotrzkowski, E. Litwin-Staszewska, M.Iwinska, T. Sochacki, R. Kucharski, and M. Bockowski, “High-temperature Properties of Electron Transport in Semi-insulating GaN:Mn Monocrystals”, The International Workshop on Nitride Semiconductors (IWN), October 09-14, 2022 Berlin, Germany.
  
• M. Zajac, P. Nita, L. Konczewicz, E. Litwin-Staszewska, R. Piotrzkowski, R. Kucharski, M. Bockowski,R. Kozlowski, P. Kaminski, “Identification and Quantitative Analysis of Point Defects in Semi-Insulating GaN:Mg Ammonothermal: Crystals, The International Workshop on Nitride Semiconductors (IWN), October 09-14, 2022 Berlin, Germany.
  
• L. Kończewicz, E. Litwin-Staszewska, M. Zajac, H. Turski, M. Bockowski, D. Schiavon, M. Chlipała, M. Iwinska, P. Nita, S. Juillaguet, S. Contreras, “Electrical transport properties of highly doped n-type GaN material”, The International Workshop on Nitride Semiconductors (IWN), October 09-14, 2022 Berlin, Germany.
  
• L. Kończewicz, M. Iwinska, E. Litwin-Staszewska, M. Zajac, H. Turski, M. Bockowski, D. Schiavon, M. Chlipała, S. Juillaguet, S. Contreras, “Negative magnetoresistivity in highly doped N-Type GaN L. Konczewicz”, The International Workshop on Nitride Semiconductors (IWN), October 09-14, 2022 Berlin, Germany.
  
• L. Konczewicz, S. Juillaguet, M. Zajac, E. Litwin-Staszewska, M. Al Khalfioui, M. Leroux, B. Damilano, J. Brault, S. Contreras, “Low temperature electrical transport properties of MBE-grown Mg-doped GaN subjected to a high temperature annealing process”, The International Workshop on Nitride Semiconductors (IWN), October 09-14, 2022 Berlin, Germany.
  
• M. Zajac, L. Konczewicz, E. Litwin-Staszewska, R. Piotrzkowski, R. Kucharski, R. Kozlowski, P. Kaminski, Observation of Nitrogen vacancies in semi-insulating ammonothermal GaN:Mg, XIV International Conference on Nitride Semiconductors (ICNS), 12-17.11.2023, Fukuoka, Japonia; plakat.