Damage in InGaN/GaN bilayers upon Xe and Pb swift heavy ion irradiation.

350 nm and 550 nm thick InGaN/GaN bilayers were irradiated with different energies (from ∼82 to ∼38 MeV) of xenon (129Xe) ions and different fluences of 1.2 GeV lead (208Pb) ions, respectively. The radiation effects of the swift heavy ions' (SHIs) bombardment were investigated using Rutherford Backscattering Spectrometry in Channeling mode (RBS/C), X-Ray Diffraction (XRD), and micro-Raman spectroscopy. To assess damage profiles, the RBS/C analysis was followed by Monte Carlo simulations using the McChasy code, revealing that InGaN is more susceptible to irradiation damage than GaN. Moreover, the simulations suggest that both randomly displaced atoms (possibly due to partial amorphization) and dislocation loops are formed. The elastic response to radiation was estimated by measuring the expansion of the c-lattice parameter. XRD revealed the presence of strain even in low fluence samples where only a small fraction of the sample volume suffered direct SHI impacts. Micro-Raman suggests that for low defect concentrations, it is dominantly biaxial, while for high defect concentrations, the simultaneous increase of hydrostatic and biaxial occurs. As a driving force of the lattice expansion, we point out the Poisson effect resulting from the pressure exerted by the SHI tracks on the surrounding undamaged crystal structure.

Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations.

The widespread adoption of gGaN in radiation-hard semiconductor devices relies on a comprehensive understanding of its response to strongly ionizing radiation. Despite being widely acclaimed for its high radiation resistance, the exact effects induced by ionization are still hard to predict due to the complex phase-transition diagrams and defect creation-annihilation dynamics associated with group-III nitrides. Here, the Two-Temperature Model, Molecular Dynamics simulations and Transmission Electron Microscopy, are employed to study the interaction of Swift Heavy Ions with GaN at the atomic level. The simulations reveal a high propensity of GaN to recrystallize the region melted by the impinging ion leading to high thresholds for permanent track formation. Although the effect exists in all studied electronic energy loss regimes, its efficiency is reduced with increasing electronic energy loss, in particular when there is dissociation of the material and subsequent formation of N2 bubbles. The recrystallization is also hampered near the surface where voids and pits are prominent. The exceptional agreement between the simulated and experimental results establishes the applicability of the model to examine the entire electronic energy loss spectrum. Furthermore, the model supports an empirical relation between the interaction cross sections (namely for melting and amorphization) and the electronic energy loss.