Epitaxial Growth of GaN Films on Atomically Stepped (0001) Lithium-niobate (LiNbO_3) Substrates

Epitaxial Growth of GaN Films on Atomically Stepped (0001) Lithium-niobate (LiNbO_3) Substrates

The structural properties of GaN films grown epitaxially on atomically-flat lithium niobate (LiNbO_3) substrates were investigated. Prior to GaN film growth, high-temperature treatment of the as-received LiNbO_3 removed surface damage and produced atomically stepped surfaces with an average roughness of ∼0.11 nm. The micro-steps were nearly parallel and periodic over the entire substrate surface. The step terrace width was ∼212 nm, and the average step height was ∼0.25 nm. GaN thin films were grown on flat surfaces with AlN buffer layers and GaN buffer layers grown at low temperature by using molecular beam epitaxy. Atomic force microscopy measurements showed a typical Ga-face GaN surface with spiral hillocks. The average roughness of the GaN film was ∼0.56 nm. X-ray diffraction (XRD) measurements indicated that the GaN (0001) plane was parallel to the (0001) plane of the LiNbO_3 substrate. The full width at half-maximum of the XRD rocking curve for GaN (0002) was ∼122.14 arcsec, which is comparable to that of highquality GaN films grown on other common substrates. Using transmission electron microscopy, we observed that the GaN epitaxial layers grown on LiNbO<SUB>3</SUB> had a crystalline relationship of (0001) GaN//(0001) LiNbO_3 with [10-10] GaN//[11-20] LiNbO_3. The successful growth of an epitaxial wide-band-gap GaN film on nonlinear optical LiNbO_3 is promising for the development of integrated multi-functional optoelectric devices on ferroelectrics.

The structural properties of GaN films grown epitaxially on atomically-flat lithium niobate (LiNbO_3) substrates were investigated. Prior to GaN film growth, high-temperature treatment of the as-received LiNbO_3 removed surface damage and produced atomically stepped surfaces with an average roughness of ∼0.11 nm. The micro-steps were nearly parallel and periodic over the entire substrate surface. The step terrace width was ∼212 nm, and the average step height was ∼0.25 nm. GaN thin films were grown on flat surfaces with AlN buffer layers and GaN buffer layers grown at low temperature by using molecular beam epitaxy. Atomic force microscopy measurements showed a typical Ga-face GaN surface with spiral hillocks. The average roughness of the GaN film was ∼0.56 nm. X-ray diffraction (XRD) measurements indicated that the GaN (0001) plane was parallel to the (0001) plane of the LiNbO_3 substrate. The full width at half-maximum of the XRD rocking curve for GaN (0002) was ∼122.14 arcsec, which is comparable to that of highquality GaN films grown on other common substrates. Using transmission electron microscopy, we observed that the GaN epitaxial layers grown on LiNbO<SUB>3</SUB> had a crystalline relationship of (0001) GaN//(0001) LiNbO_3 with [10-10] GaN//[11-20] LiNbO_3. The successful growth of an epitaxial wide-band-gap GaN film on nonlinear optical LiNbO_3 is promising for the development of integrated multi-functional optoelectric devices on ferroelectrics.