Anisotropic Effects in Ion-implanted β-Ga₂O₃

β-Ga2O3 is an emerging wide-bandgap semiconductor with a room-temperature bandgap of ∼ 4.9 eV and high breakdown field (∼ 8 MV/cm), which is promising for high-power electronics and deep-ultraviolet optoelectronic devices. However, a full comprehension of the effects of ion implantation — a key enabling technology in the semiconductor industry — is still amiss for this material.

In this context, this thesis presents a systematic investigation of ion-implantation-induced anisotropic effects in β-Ga2O3, using 250 keV Cr implantation as a case study by combining experimental techniques such as High-Resolution X-Ray Diffraction (HRXRD) and Rutherford Backscattering Spectrometry in Channelling mode (RBS/C) with Molecular Dynamics (MD) simulations. Implantation into (100)-oriented samples reproducibly produces self-rolled microtubes above a threshold fluence of ∼ 1 × 1014 cm−2 (∼ 0.3 dpa), which can be unrolled into nanomembranes upon annealing at 500 ◦C.

This process is independent of the implanted species and the thickness of the membranes depends on the ion energy. The excellent agreement between experiment and simulation allowed the identification of compressive stress accumulated along the [010] direction as the driving force for the self-rolling phenomenon. A general anisotropic-elastic model for implantation-induced stress and strain was developed, revealing tensile stresses along the directions in the a − c plane and compressive stress along the [010] direction.

The observed strain is a superposition of defect-related eigenstrain and elastic strain due to the substrate response. In excellent agreement with experiment, these strains cancel in-plane but yield a net out-of-plane strain via the Poisson effect. At higher damage levels, an orientation-independent β-to-γ phase transformation was observed via pole figures obtained both experimentally and computationally, obeying the crystallographic relationship (010)β ∥ (110)γ and [102]β ∥ [112]γ. Finally, a systematic HRXRD and RBS/C study revealed direction-dependent defect visibility, apparent accumulation and recovery rates under annealing.

In particular, it was possible to conclude that point defects mainly contribute to the out-of-plane strain and are efficiently removed at ∼ 500 ◦C, whereas removing extended defects requires higher temperatures. Overall, this work highlights the interplay of crystallography, elastic anisotropy and defect dynamics in ion-implanted β-Ga2O3, providing experimental and computational methodologies relevant for both fundamental studies and device-oriented processing.