(Invited) Epitaxial Growth and Characterization of Ga₂O₃ Polymorphs

Gallium oxide (Ga 2 O 3 ) is an ultra-wide band gap semiconductor with extraordinary potential for high-power, high-frequency, and high-temperature electronics and UV optoelectronics. The existence of stable and metastable phases, or polymorphs, of Ga 2 O 3 presents challenges and opportunities for future device development. β-Ga 2 O 3 is the thermodynamically stable phase and occurs in melt-grown, single-crystal substrates. The metastable phases, which have been demonstrated in pure- or mixed-phase form in epitaxial films, also possess ultra-wide bandgaps. Intriguing properties, such as ferromagnetism and ferro- and/or piezoelectricity, have been reported for certain phases and could enable new types of devices based on Ga 2 O 3 . Controlled growth of different Ga 2 O 3 polymorphs could also lead to structurally-matched alloys, e.g., with In 2 O 3 (E g = 3.7 eV) and Al 2 O 3 (E g = 8.8 eV), to modulate bandgaps. In this presentation an overview of the stable and metastable Ga 2 O 3 phases in terms of properties and growth methods will be given. We will present results from chemical vapor deposition, highlighting how certain conditions (e.g., temperature, growth rate, substrate, and impurity content) can affect the resulting polymorph(s). Characterization of phase composition, microstructure, and morphology using x-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy will be shown for each type of film.