Single crystal AlN substrate can be provided with specifications as found in https://www.powerwaywafer.com/aln-substrate.html.

AlN single crystal is the direct bandgap semiconductor material with the largest bandgap width (6.2 eV), which has excellent characteristics such as extremely high breakdown field strength, excellent thermal conductivity, stable physical and chemical properties. Moreover, AlN single crystal has very small lattice and thermal mismatch with GaN and AlGaN, and is considered the best substrate for III-V epitaxial materials. It has broad application prospects in deep ultraviolet detectors, deep ultraviolet LEDs, deep ultraviolet LDs, and microwave high-power fields.

Currently, the Physical Gas Transport (PVT) method is the mainstream method for preparing AlN bulk single crystals. However, the primary factor restricting the development of PVT based AlN single crystal growth technology is the acquisition of high-quality AlN seed crystals, as well as the correlation between growth conditions and growth modes when AlN seed crystals grow homogeneously.

Researchers has used PVT method to grow high-quality AlN single crystals on self-made AlN seed crystals. The surface morphology of AlN single crystals under different growth modes (three-dimensional island and single helix growth centers) was observed. On the basis of optimizing the thermal field structure, it was found that the surface temperature of AlN seed crystals plays an important role in crystal growth, and the growth conditions directly determine the crystal growth mode. It is worth noting that the half width (FWHM) of the (002) and (102) diffraction peaks of AlN single crystals grown in the single helix growth center mode are 65 and 36 arcsec, respectively. An AlN buffer layer and a high Al component AlxGa1-xN thin film were sequentially epitaxial grown on a high-quality AlN single crystal substrate using MOCVD. The surface of the AlN buffer layer exhibits good surface crystallization quality. The Al component of AlxGa1-xN epitaxial thin film is 0.54, and the half width at half maximum (FWHM) of (002) and (102) reflections of Al x Ga1-xN are 202 and 496 arc seconds, respectively. The above research results indicate that compared to SiC or sapphire substrates, AlN single crystal substrates exhibit superior advantages in homogenous epitaxial growth of AlN and high Al component AlGaN films.

Fig.1 Surface morphology of AlN single crystal

This study will further guide the preparation of high-quality AlN single crystals and promote the development of AlGaN epitaxy and related devices.

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