Synthesis of thin single-crystalline $\alpha$-Cr$_2$O$_3$ layers on sapphire substrates by ultrasonic-assisted chemical vapor deposition

Single-crystalline $\alpha$-Cr$_2$O$_3$ layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700–850$^\circ$C. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800$^\circ$C, continuous layers with a thickness of about 1 $\mu$m were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of $\sim$350 nm. The full width at half maximum of the rocking curve for reflection 0006 was $\sim$300 arcsec.