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Energy threshold for swift heavy ion tracks in GaN

The passage of a swift heavy ion through a solid material can result in permanent damage called ion track. The most common description of the ion track formation, the thermal spike model, suggests that the kinetic energy of the projectile that is deposited as dense electronic excitation along the ion trajectory, can lead to melting of the material. In this case, ion tracks originate from the quenching of the molten phase on the nanosecond time scale, resulting in an amorphous inclusion. Thus, the threshold for ion track formation and the track size depend on ion beam parameters and material properties. One of the most important material properties related to the swift heavy ion track formation is the energy bandgap [1, 2]. In this work we present experimental results of ion track formation in thin GaN epi-layer grown by MOVPE on sapphire. As a follow up of our previous work on the wide bandgap semiconductors SrTiO3 (Eg = 3 eV) [3] and TiO2 (Eg = 3 eV), the material investigated here presents an opportunity for further studies since its bandgap energy is Eg = 3.4 eV. The GaN samples were irradiated by swift heavy ions under both normal and grazing angle of incidence. Irradiation parameters were chosen to investigate the material’s response close to the ion track formation threshold, and to complement previous works using higher energy ion beams [4, 5]. We investigated ion irradiation effects both on the material surface by means of AFM and GISAXS and in the bulk by means of RBS/c. Our results are discussed in the framework of the thermal spike model. [1] M. Toulemonde et al., Nucl. Instrum. Meth. B 166-167, 903 (2000). [2] G. Szenes, Nucl. Instrum. Meth. B 269, 2075 (2011). [3] M. Karlušić et al., New J. Phys. 12, 043009 (2010). [4] S. Mansouri et al., Nucl. Instrum. Meth. B 266, 2814 (2008). [5] S.O. Kucheyev et al, J. Appl. Phys. 95, 5360 (2004).

ion track; swit heavy ion; GaN

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