Gallium Oxide and Oxynitrides: Achieving Thin Film Crystallinity at Low Thermal Budgets

  • Author / Creator
    Rafie Borujeny, Elham
  • Growing demand for electrical energy calls for more efficient electronic devices not only in terms of performance but also in terms of energy-efficient fabrication processes. With traditional semiconductors (such as silicon) reaching their limits in electrical power handling, alternative semiconducting materials have been considered to overcome fundamental material limitations and meet the stringent requirements of efficiency, reliability, and cost effectiveness. Gallium nitride (GaN) has been one of the frontrunners to replace silicon for power electronic and optoelectronic applications. However, gallium oxide (Ga2O3) has recently attracted considerable attention as a suitable candidate that can compete with and complement GaN electronics and lead to more efficient devices. Even though Ga2O3 is not a new material, its application as a wide bandgap semiconductor in electronic devices is new. For electronic applications, two crystalline Ga2O3 phases are of interest, α-Ga2O3 and β-Ga2O3. However, high quality crystalline Ga2O3 thin films can currently be obtained on very limited substrates in specific process conditions or at high temperatures. This work demonstrates a number of novel strategies for energy-efficient fabrication of high quality crystalline films of gallium oxide and oxynitrides as emerging wide bandgap semiconductors with applications in a broad range of electronic devices. Atomic layer deposition (ALD) is used to achieve dense and pinhole-free films of gallium oxide at low thermal budgets (with a special focus on temperatures < 300°C). After determining the onset temperature for crystallinity formation to be 190°C (the lowest reported value in the literature so far), the deposition process conditions are presented that result in either amorphous or mixed-phase crystalline films with superior properties. Furthermore, for the first time in the literature, by taking advantage of the unique crystallographic features of Ga2O3, a universal and robust approach is proposed to control the crystallinity of Ga2O3 thin films in situ and achieve single-phase α-Ga2O3 films on GaN-compatible non-native substrates at low thermal budgets. The step-by-step process is then revised so that the energetics of the process can lead to high quality epitaxial β-Ga2O3 films at low temperatures. Discovering universal methods to obtain single-phase crystalline films of α-Ga2O3 and β-Ga2O3 are major novel contributions of this work. In addition, this work showcases a series of ALD depositions for controlled incorporation of oxygen in the crystal structure of GaN at low temperature to obtain gallium oxynitride films with tunable structure and properties.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.