Dynamic Recovery in Au Ion Irradiated Gallium Nitride
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Dynamic Recovery in Au Ion Irradiated Gallium Nitride W. Jiang and W. J. Weber Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 L. M. Wang and K. Sun Department of Nuclear Engineering & Radiological Sciences, the University of Michigan, Ann Arbor, MI 48109 ABSTRACT Gallium nitride single crystals were irradiated using energetic Au2+ ions to two fluences at room temperature. Two different damage levels and depth profiles that are characterized by nearsurface damage accumulation and deeper-region damage saturation were produced. Thermal annealing at 873 K resulted in disorder recovery only in the near-surface region at low fluence. However, simultaneous irradiation with 5.4 MeV Si2+ ions during annealing at 873 K induced significant recovery over the entire damage profile at both low and high fluences. Results from high-resolution transmission electron microscopy show recovery of the crystal structure in the highly disordered surface region following the Si2+ ion irradiation. The irradiation-assisted recovery is primarily attributed to defect-stimulated recovery and epitaxial recrystallization processes due to the creation of mobile Frenkel pairs. INTRODUCTION Gallium nitride (GaN) is a wide bandgap semiconductor material that has attracted extensive investigations of ion-implantation effects associated with the fabrication of advanced electronic and optoelectronic devices [1,2]. Previous studies have indicated that post thermal annealing at moderate to high temperatures (< 1200 K) does not significantly recover the lattice disorder induced by ion implantation [3,4]. Higher-temperature annealing above 1273 K can destroy the GaN stoichiometry [5] and special techniques (such as proximity geometry and nitrogen pressure) must be applied to prevent the material from decomposition and evaporation. Only at ultrahigh temperatures (1773 K) and under an overpressure (~15 kbar) of nitrogen, can thermal annealing result in the complete removal of implantation-induced damage without macroscopic surface decomposition [1,6]. Thus, further research is required to explore alternative methods for damage recovery without involving such harsh annealing conditions. It is well known that ion irradiation not only displaces lattice atoms, but can also enhance defect diffusion in semiconductors and other materials [7]. The elastic collisions produce defects that can stimulate damage recovery and epitaxial recrystallization processes, while the inelastic collisions can lead to excited states that affect local energy barriers to recombination and diffusion. These dynamic recovery processes can enhance or stimulate recovery of disorder that is not otherwise thermally recoverable at the same temperature. Recent studies have indicated that a reconstruction of amorphized GaN occurs following light- or heavy-ion irradiation in GaN [8,9]. It also has been reported that there is an efficient dynamic recovery in GaN during ion implantation at and above liquid-nitrogen temperature [1,3,10]. This study r
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