Growth and Characterization of Nonpolar Nanoporous AlN by Inward Conversion of (004) γ-LiAlO₂ Crystals

In this study, an innovative nonpolar nanoporous AlN growth technology was successfully developed, which realized in situ nitrided growth of nonpolar AlN by γ-LiAlO2 (LAO) crystals through the crystal elements expelled and recrystallization (CEER) method. In this way, we can effectively avoid the quantum-confined Stark effect by the growth of nonpolar AlN, paving the way for the fabrication of high quantum efficiency AlN-based optoelectronic devices. The prepared AlN crystalline was fully characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The pore structure has an average pore size of about 40–50 nm, making it a great potential as a patterned substrate for epitaxial lateral overgrowth and a template for GaN-based LED devices. The rocking curve of XRD shows a full width at half-maximum (fwhm) of 0.75°, indicating relatively good crystalline quality. The phonon frequency of the E2 (high) phonon mode in the Raman spectrum is shifted to 657.7 cm–1, which is slightly blue-shifted compared with the E2 (high) phonon mode of the ideal AlN crystal, reflecting the slight compressive stress in the crystal structure. In addition, the AlN crystal observed by TEM has a depth of more than 4 μm, further confirming the uniformity of the crystal and the excellent three-dimensional connectivity of the pore structure. The TEM images also show that the AlN crystalline prepared by the CEER method has a lower defect density, which is conducive to greatly improving the performance of AlN-based devices. This technique enables a novel approach to synthesizing a-plane AlN, a significant advancement for the production of high-quality nonpolar AlN materials and the development of nonpolar LEDs.