Adsorption controlled homoepitaxial growth of c-plane sapphire by thermal laser epitaxy

Its low cost, superior properties over silicon, high quality wafer availability, and the possible integration with silicon have established sapphire as widely used substrate material.[1] The ultra-wide bandgap and attractive dielectric constant of sapphire equally promise to reach regimes of semiconductor electronics and photonics thought to be impossible.[2] A cornerstone for further advancing the use of sapphire is the to growth of high quality homoepitaxial sapphire films. However, epitaxial films of c-plane oriented sapphire, one of the most common cuts of sapphire, have so far been out of reach due to the preferred formation of the Al₂O₃ γ-phase.[3] Epitaxial films grown on other cuts of sapphire usually suffer from a bandgap reduction.[2,4]<br/>In the presentation, I will demonstrate that the extensive parameter space available in TLE solves those problems.[5] The CO₂-laser driven substrate heating system allows to heat sapphire substrates to their melting point. The high accessible and precisely controllable temperatures enable a smooth sapphire substrate preparation – the first step for successful homoepitaxy.[6] I further present how the crystal quality and surface smoothness of homoepitaxial sapphire increase with increasing substrate temperature in case the growth is performed in the adsorption-controlled mode. Even at high temperatures growth rates &gt; 1 υm/h are realized. At a growth temperature of 1600 °C, the films were found to be practically undistinguishable from the underlying substrate regarding their crystallinity and optical properties, even exceeding the substrate’s purity.<br/><br/><b>References</b><br/><br/>[1] M.S. Akselrod, F.J. Bruni, “Modern trends in crystal growth and new applications of sapphire,” <i>J. Cryst. Growth</i>, 360, pp. 134-145, 2012.<br/>[2] R. Jinno <i>et al.</i>, “Crystal orientation dictated epitaxy of ultrawide-bandgap 5.4- to 8.6-eV α-(AlGa)₂O₃ on m-plane sapphire”, <i>Sci. Adv., </i>7, eabd5891, 2021.<br/>[3] H. Okumura, “Sn and Si doping of α-Al₂O₃ (10-10) layers grown by plasma-assisted molecular beam epitaxy”, <i>JJAP</i>, 61, 125505, 2022<i>.</i><br/>[4] Z. Chen <i>et al</i>. “Epitaxial growth of (AlxGa1- x)2O3 thin films on sapphire substrates by plasma assisted pulsed laser deposition.” <i>AIP Advances</i> 11, 2021.<br/>[5] W. Braun and J. Mannhart, “Film deposition by thermal laser evaporation,” <i>AIP Advances,</i> 9, 085310, 2019.<br/>[6] W. Braun <i>et al.</i>, “<i>In situ</i> thermal preparation of oxide surfaces”, <i>APL Mater.,</i> 8, 071112, 2020.