Growth of Single-Crystalline GaN Films on Ga-Free Langasite-Type Crystals by Metal-Organic Chemical Vapor Deposition

Langasite (La3Ga5SiO14, LGS) family crystals are known for their piezoelectric properties, which make them widely applicable in surface acoustic wave (SAW) devices. The group-III metal nitrides formed on LGS substrates are found to enable significant extension of SAW devices to higher-frequency ranges. However, the Ga element in LGS crystals is observed to volatilize in H-2 at high temperatures, forming Ga droplets and degrading the film quality. This study reports the growth of GaN films on the Ga-free LGS-type crystal Ca3NbAl3Si2O14 (CNAS) by metal-organic chemical vapor deposition (MOCVD), and the CNAS is stable in MOCVD. The as-grown GaN films are continuous and smooth with a roughness of 0.369 nm. The epitaxial relationship between GaN and CNAS is GaN(0001)//CNAS(0001) and GaN(10-12)//CNAS(21-32). The mixed dislocations are found to be dominant type of dislocations of the GaN films on CNAS. The GaN films also exhibit good optical properties and a compressive stress of 0.17 GPa. Thus, the results indicate that the Ga-free LGS-type crystals have great potential for applications in the epitaxial growth of GaN materials.