Characteristic luminescence in the high crystalline alpha-Ga2O3 grown on the thin-wall single crystal Al2O3

<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" dir="auto" id="d27193e153">A high-quality alpha-Ga ₂O ₃ thin film was successfully grown on a single-crystal Al ₂O ₃ thin-wall channel structure. The alpha- Ga ₂O ₃ crystals developed a 3-fold symmetry based on the Al ₂O ₃ surface, resulting in domain boundaries due to slight rotations within the mosaic structure. <a class="xref-link" href="#fg001">Figure 1(a)</a> illustrates a schematic view of the alpha- Ga ₂O ₃ thin films, with the blue area indicating the sampling zone for transmission electron microscopy observations. <a class="xref-link" href="#fg001">Figure 1(b)</a> presents a brightfield image of the transition region between lateral and vertical growth, while <a class="xref-link" href="#fg001">Figure 1(c)</a> shows the ADF image of this same transition region. <p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" dir="auto" id="d27193e196">The boundaries of the Anti-phase domains (APDs) were identified with weak contrast, and changes in the growth direction were observed in the valley region. APDs were confirmed through convergent-beam electron diffraction (CBED), indicating that they formed during the nucleation stage, likely due to unstable or uneven Al-O bonding on the Al ₂O ₃ surface. The in-phase domains and APD boundaries exhibited bright contrast in ADF imaging, attributed to local strain resulting from crystallographic rotation rather than variations in gallium concentration. <p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" dir="auto" id="d27193e204">Cathodoluminescence (CL) measurements taken within transmission electron microscopy (TEM) indicated that the bandgap energy of alpha- Ga ₂O ₃ is approximately 5.56 eV, corresponding to a near-band-edge transition at around 223 nm. While the heights and positions of the luminescence peaks vary slightly across different regions, four distinct peaks and a broad tail in the wavelength spectrum are consistently observed throughout the crystal. Two-dimensional mapping within a specific wavelength range reveals clear differences between the interior domain, in-phase domain boundary, and APD boundary, with a notable luminescence peak at 350 nm specifically at the APD boundary. <div xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="fig panel" id="fg001"> <a class="named-anchor" id="fg001"> <!-- named anchor --> </a> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/81060195-3e13-484a-a12d-02fa9722e915/ScienceOpen/image/366_6720cda2dad45-YoungwoonKimAPMC2025_fig1.jpg"/> </div> <div class="panel-content"> <div class="label">Figure 1</div> <div class="caption" id="d27193e215"> <p class="first" dir="auto" id="d27193e216">(a) illustrates a schematic representation of the alpha-Ga ₂O ₃ thin film growth on the thin Al ₂O ₃ bridge. (b) shows an ADF image from the transition region of the merged valley, and (c) reveals a high-magnification view of the transition region, highlighting the two distinct growth modes of the anti-phase domains. </div> </div> </div>