Formation of γ-Ga2O3 by ion implantation: Polymorphic phase transformation of β-Ga2O3

Abstract

Ion implantation induced phase transformation and the crystal structure of a series of ion implanted β-Ga2O3 samples were studied using electron diffraction, high resolution transmission electron microscopy, and scanning transmission electron microscopy. In contrast to previous reports suggesting an ion implantation induced transformation to the orthorhombic κ-phase, we show that for 28Si+, 58Ni+, and stoichiometric 69Ga+/16O+-implantations, the monoclinic β-phase transforms to the cubic γ-phase. The γ-phase was confirmed for implantations over a range of fluences from 1014 to 1016 ions/cm2, indicating that the transformation is a general phenomenon for β-Ga2O3 due to strain accumulation and/or γ-Ga2O3 being energetically preferred over highly defective β-Ga2O3.

Size-Dependent Phase Transition in Ultrathin Ga2O3 Nanowires

“…Considering both the initial and final β-phases, the (600) β plane occupies a larger surface area than the (12) β plane, allowing NWs to retain their surface properties as size decreases. Finally, according to our current results, the β- to γ-phase transition upon ion implantation reported previously , could be mainly induced by the surface energy reduction rather than the strain accumulation …”

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

“…To a lesser extent, γ-Ga 2 O 3 , with the structure of a defect spinel [ 1 , 2 , 3 ], is also currently being studied. This is believed to be formed during a transitory phase when α-Ga 2 O 3 or κ-Ga2O 3 [ 4 ] is heated up, or when the heavy ion implantation of β-Ga 2 O 3 is carried out [ 5 ]. Researchers are mainly interested in the stable β-Ga 2 O 3 polymorph.…”

“…They also exhibit good switching speeds due to the high saturation velocity of electrons. Photodetectors show excellent photosensitivity in the far-UV-C spectral range, with a high rejection ratio for photosensitivity in the visible and near-UV range; this is owing to the very large bandgap and the reasonably low density of defects, which create centers with deep levels in the gap [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Both n-type bulk crystals and epi-layers can be controllably grown with doping over a wide range of concentrations, as well as via semi-insulating, by incorporating Fe, Mg or N acceptors [ 2 ].…”

“…Bulk crystals and epi-structures of β-Ga 2 O 3 are commercially available (see e.g., [ 11 ]). Prototype devices of various types with characteristics that exceed those based on more mature wide-bandgap materials have been demonstrated by many research groups and are approaching the stage at which they will become commercially available [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. The remaining problems in this materials system are related to the absence of defects and impurities that are suitable for viable p-type doping, the low thermal conductivity of β-Ga 2 O 3 , considerable anisotropy related to low levels of lattice symmetry, and the relatively low electron mobility [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ].…”

“…Thus, growth on heavily lattice mismatched hexagonal GaN, AlN and SiC has resulted in the formation of films of pure κ-Ga 2 O 3 . It has been also suggested that high levels of strain in heavily disordered β-Ga 2 O 3 when exposed to high-dose ion implantation could give rise to the formation of defective κ-Ga 2 O 3 layers [ 38 , 39 ]; however, this hypothesis has been challenged in recent papers [ 5 , 40 ].…”