Influence of HCl Support on the α-Ga₂O₃ Thin Film Properties Growth by Mist Chemical Vapor Deposition

Gallium Oxide (Ga₂O₃) is one of the promising materials as ultrawide bandgap semiconductors for power devices and optoelectronics devices. Among 5 phases (α-, β-, γ-, δ-, and ε- phases) which Ga₂O₃ can be crystallized, α-Ga₂O₃ has the widest bandgap of 5.3 eV and it can be controlled the properties by changing the composition of a-(M_xGa_1-x)₂O₃ alloys [M = Fe, Cr, In, Al]. Thus, α-Ga₂O₃ is obtaining more attention. Recently, it was reported that HCl affected α-, β-, and ε-Ga₂O₃ growth selectively by Metal organic chemical vapor deposition (MOCVD) and halide vapor phase epitaxy (HVPE).^1,2) Additionally, our group reported that the HCl can be improved the surface roughness of α-Ga₂O₃ by mist chemical vapor deposition (mist CVD).³⁾ However, more investigations are necessary because the mechanism and the influence of HCl on the Ga₂O₃ thin film properties have not been cleared. In this work, the Ga precursor was changed from previous research and the dependence of the crystallinity and other properties of α-Ga₂O₃ thin film by changing HCl supply was investigated.<br/>α-Ga₂O₃ thin films were fabricated by a 3^rd generation mist CVD^3,4) which consists of multiple solution chambers and a fine channel type reactor. Two solutions of i) Gallium acetylacetonate dissolved in the mixture of deionized water and HCl as Ga source and ii) HCl diluted by deionized water as HCl source were prepared and the supply amount of Ga and HCl were controlled by changing the solution concentration and carrier gas of each solution chamber. As a result of X-ray rocking curve for crystallinity evaluation, it was found that the crystallinity depended only on the film thickness regardless of the experimental conditions, and the crystallinity improved as the film thickness increased. Specifically, the full width at half maximum (FWHM) was 137.1 arcsec when the film thickness was 107 nm, 38.5 arcsec when the film thickness was 515 nm, and 32.4 arcsec when the film thickness was 32.4 arcsec. However, it was found that HCl can be improved surface roughness of α-Ga₂O₃,³⁾ thus, this results indicated that HCl can improve the surface roughness without affecting crystallinity.<br/>In addition to reporting more detailed results in this conference, I would like to explain the comparison of the effect of HCl on α-Ga₂O₃ thin film properties with different Ga precursor.<br/>1) H. sun et al, Cryst. Growth Des. <b>18</b>, 2370-2376 (2018)<br/>2) Y. Yao et al, Mater. Res. Lett. <b>6</b>(5), 268 (2018)<br/>3) T. Yasuoka et al, AIP Adv. <b>11</b>, 04123 (2021)<br/>4) P. Rutthongjan et al, Jpn. J. Appl. Phys., Part 1 <b>58</b>, 035503 (2019)