BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Anisotropic Effects in Ion-implanted β-Ga₂O₃ DTSTART:20260904T100000Z DTEND:20260904T120000Z DTSTAMP:20260808T053825Z UID:ea1d2944-9f14-4028-96cc-84188d41c98c SEQUENCE:3 CREATED:20260728T104648Z DESCRIPTION: β-Ga2O3 is an emerging wide-bandgap semiconductor with a roo m-temperature bandgap of ∼ 4.9 eV and high breakdown field (∼ 8 MV/cm) \, which is promising for high-power electronics and deep-ultraviolet opto electronic devices. However\, a full comprehension of the effects of ion i mplantation — a key enabling technology in the semiconductor industry — is still amiss for this material. In this context\, this thesis presen ts a systematic investigation of ion-implantation-induced anisotropic effe cts in β-Ga2O3\, using 250 keV Cr implantation as a case study by combini ng experimental techniques such as High-Resolution X-Ray Diffraction (HRXR D) 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 fl uence of ∼ 1 × 1014 cm−2 (∼ 0.3 dpa)\, which can be unrolled into n anomembranes upon annealing at 500 ◦C. This process is independent of th e 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] direc tion as the driving force for the self-rolling phenomenon. A general aniso tropic-elastic model for implantation-induced stress and strain was develo ped\, 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 th e substrate response. In excellent agreement with experiment\, these strai ns cancel in-plane but yield a net out-of-plane strain via the Poisson eff ect. At higher damage levels\, an orientation-independent β-to-γ phase t ransformation was observed via pole figures obtained both experimentally a nd computationally\, obeying the crystallographic relationship (010)β ∥ (110)γ and [102]β ∥ [112]γ. Finally\, a systematic HRXRD and RBS/C s tudy revealed direction-dependent defect visibility\, apparent accumulatio n and recovery rates under annealing. In particular\, it was possible to c onclude that point defects mainly contribute to the out-of-plane strain an d are efficiently removed at ∼ 500 ◦C\, whereas removing extended defe cts requires higher temperatures. Overall\, this work highlights the inter play of crystallography\, elastic anisotropy and defect dynamics in ion-im planted β-Ga2O3\, providing experimental and computational methodologies relevant for both fundamental studies and device-oriented processing. LAST-MODIFIED:20260728T105042Z LOCATION:Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST URL:http://df.vps.tecnico.ulisboa.pt/pt/eventos/anisotropic-effects-in-ion -implanted-%CE%B2-ga%E2%82%82o%E2%82%83/ X-ALT-DESC;FMTTYPE=text/html:

β-Ga2O3 is an eme rging 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 mater ial.

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

This process is independent of the implanted s pecies and the thickness of the membranes depends on the ion energy. The e xcellent agreement between experiment and simulation allowed the identific ation of compressive stress accumulated along the [010] direction as the d riving force for the self-rolling phenomenon. A general anisotropic-elasti c model for implantation-induced stress and strain was developed\, reveali ng tensile stresses along the directions in the a − c plane and compress ive stress along the [010] direction.

The observed strain is a s uperposition of defect-related eigenstrain and elastic strain due to the s ubstrate 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 tran sformation was observed via pole figures obtained both experimentally and computationally\, obeying the crystallographic relationship (010)β ∥ (1 10)γ and [102]β ∥ [112]γ. Finally\, a systematic HRXRD and RBS/C stud y revealed direction-dependent defect visibility\, apparent accumulation a nd recovery rates under annealing.

In particular\, it was possib le to conclude that point defects mainly contribute to the out-of-plane st rain and are efficiently removed at ∼ 500 ◦C\, whereas removing extend ed defects requires higher temperatures. Overall\, this work highlights th e interplay of crystallography\, elastic anisotropy and defect dynamics in ion-implanted β-Ga2O3\, providing experimental and computational methodo logies relevant for both fundamental studies and device-oriented processin g.

END:VEVENT END:VCALENDAR