Mechanisms of damage formation in AlGaN alloys implanted with Ar and Eu ions

(1) IPFN, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, km 139.7, 2695-066 Bobadela LRS, Portugal
(2) Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Max-Wien-Platz 1, 07743 Jena, Germany
(3) Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Group-III-nitrides, in particular AlxGa1-xN alloys, are important optoelectronic materials used for UV light emitting devices and high electron mobility transistors (HEMTs).  Ion implantation is an important technique for selective area doping and implant isolation [1]. However, this technique produces damage which degrades the properties of materials. In III-nitride alloys, the formation of implantation damage is still largely unexplored and not yet fully understood.      In this study, the damage formation mechanisms and radiation resistance of AlxGa1-xN alloys is investigated combining Rutherford Backscattering Spectrometry/Channelling (RBS/C) and X-ray diffraction (XRD) in order to assess the damage profiles and the elastic response of the material to radiation. AlxGa1-xN alloys covering the entire compositional range (0 ≤ x ≤ 1) were implanted at room temperature with 200 keV Ar ions, to avoid chemical effects, and fluences ranging from 1×1013 to 2×1016 Ar/ cm2.   XRD 2 theta-omega curves show that implantation leads to the incorporation of large lattice strain in the implanted layer which increases with the fluence. Above a threshold fluence, an abrupt change of the elastic properties of the crystals is observed and strain saturates in the entire implanted region. This threshold fluence is reached earlier for GaN than for AlGaN alloys. Surprisingly, RBS/C reveals higher defect levels for high fluence implantations in samples with high AlN concentrations. These results contrast reports on rare earth implantation in AlGaN and ion implantation in AlGaAs alloys which reveal a strong increase of radiation resistance with increasing AlN content [2, 3]. The effect of AlN content on dynamic annealing processes and radiation resistance of AlGaN alloys as well as the differences between Ar and Eu implantation will be discussed.   

[1] Taube et al. MRS. Proceedings 1635 (2014) 9
[2] Breeger et al. NIMB 148 (1999) 468 [3] Fialho et al. NIMB 273 (2012) 149