In this study, we report the effect of pre-treatment of alpha-Ga₂O₃ grown on a sapphire substrate by halide vapor phase epitaxy (HVPE). During the pre-treatment process, 10 sccm of GaCl gas was injected to the sapphire substrate at 470℃. The surface morphologies of the alpha-Ga₂O₃ layers grown with various pre-treatment time (3, 5, and 10 min) were flat and crack-free. The transmittance of the alpha-Ga₂O₃ epi-layers was measured to analyze their optical properties. The transmittance was over 80% within the range of visible light. The strain in the alpha-Ga₂O₃ grown with a pre-treat 5 min was measured, and was found to be close to the theoretical XRD peak position. This can be explained by the reduction of strain having caused a lattice mismatch between the alpha-Ga₂O₃ layer and sapphire substrate. The calculated dislocation density of the screw and edge were 2.5×10⁵ cm^-2 and 8.8×10⁹ cm^-2, respectively.

We demonstrated a crack-free α-Ga₂O₃ on sapphire substrate by horizontal halide vapor phase epitaxy (HVPE). Oxygen-and gallium chloride-synthesized Ga metal and HCl were used as the precursors, and N₂ was used as the carrier gas. The HCl flow and growth temperature were controlled in the ranges of 10~30 sccm and 450~490℃, respectively. The surface of α-Ga₂O₃ template grown at 470℃ was flat and the root-mean-square (RMS) roughness was ~2 nm. The full width at half maximum (FWHM) values for the symmetric-plane diffractions, were as small as 50 arcsec and those for the asymmetric-plane diffractions were as high as 1,800 arcsec. The crystal quality of α-Ga₂O₃ on sapphire can be controlled by varying the HCl flow rate and growth temperature.

We demonstrated that self-separation FS-GaN (freestanding-GaN) was grown on MELO (maskless epitaxially lateral overgrowth) GaN template by horizontal HVPE (hydride vapor phase epitaxy). Before thick GaN grwoth, MELO GaN template was grown on patterned GaN template by MOCVD (metal organic chemical vapor deposition). The laterally overgrown GaN would consist of a continuous well coalesced layer. The mixed TDD (threading dislocation density) of seed and wing region were 8 × 10⁸ cm-2 and 7 × 10⁷ cm^-2, respectively. After thick GaN grown by HVPE, the self-separation between thick GaN and sapphire substrate was generated at seed region. The regions of self-separation for FS-GaN and sapphire were observed by FE-SEM. Moreover, Raman results indicated that the compressive strain of seed and wing regions at FS-GaN substrate were slightly released compared to that of thick GaN grown on conventional GaN template. The optical properties of the FS-GaN substrate were examined by using PL (photoluminescence). The PL exhibited that donor bound exciton and donor acceptor pair were observed at low temperature. The effects on optical and structural properties of FS-GaN substrate have been discussed in detail.

In this paper, GaN film was grown on AlN/PSS by hydride vapor phase epitaxy compared with GaN on planar sapphire. Thin AlN layer for buffer layer was deposited on patterned sapphire substrate (PSS) by metal organic chemical vapor deposition. Surface roughness of GaN/AlN on PSS was remarkably decreased from 28.31 to 5.53 nm. Transmittance of GaN/AlN grown on PSS was lower than that of planar sapphire at entire range. XRD spectra of GaN/AlN grown on PSS corresponded the wurzite structure and c-axis oriented. The full width at half maximum (FWHM) values of ω-scan X-ray rocking curve (XRC) for GaN/AlN grown on PSS were 196 and 208 arcsec for symmetric (0 0 2) and asymmetric (1 0 2), respectively. FWHM of GaN on AlN/PSS was improved more than 50% because of lateral overgrowth and AlN buffer effect.

Citations

• AlGaN/GaN HEMTs with a magnetron-sputtered AlN buffer layer
  Chunxiao Zhao, Ni Zeng, Bingzhi Zou, Qiao Sun, Jinyi Wang, Kejun Wei, Zeyu Huang, Tiankai Wang, Jingjing Lin, Yian Yin
  Microelectronics Journal.2023; 140: 105926.     CrossRef

In this paper, high quality AlN layers were regrown on AlN nanopillar structure with SiO2-dots by HVPE. Surface morphology of AlN layer regrown exhibited flatter than a conventional AlN template. The laterally overgrown AlN regions would consist of a continuous well coalesced layer with lower dislocation density than in the template because of the dislocation blocking and dislocation bending effects. Moreover, result of Raman spectroscopy suggest that the AlN nanopillar structure with SiO2-dots relieves the strain in the AlN layer regrown by HVPE.