Solid-phase crystallization of amorphous Ga2O3/sapphire(0001) thin films monitored using in-situ multimodal X-ray probe technique

Abstract

We investigated the crystallization behavior and structural evolution of amorphous Ga2O3 thin films deposited on sapphire (0001) substrates via solid phase epitaxy (SPE) using a synchrotron-based in-situ multimodal X-ray probe station. Real-time X-ray diffraction (XRD) and electrical conductance measurements during post-annealing revealed that crystallization into the alpha-Ga2O3 phase begins at approximately 500 degrees C, accompanied by a marked increase in conductance owing to thermally activated carrier transport. High-resolution XRD confirmed the formation of a high-quality alpha-Ga2O3 film with the c-axis oriented along the surface normal and fully relaxed lattice parameters in the in-plane and out-of-plane directions. Azimuthal angle scans revealed six-fold symmetry, confirming epitaxial in-plane alignment between the alpha-Ga2O3 film and sapphire (0001) substrate. Rocking curve analysis yielded dislocation densities of similar to 1.07 x 10(8) (screw) and similar to 4.34 x 10(9) cm(-2) (edge), corresponding to a total threading dislocation density of approximately 4.45 x 10(9) cm(-2), which is comparable to previously reported values for directly grown alpha-Ga2O3 films. These findings demonstrate that SPE is a promising alternative to conventional epitaxy for producing high-quality alpha-Ga2O3 thin films. This approach enables phase-selective crystallization with excellent structural quality, without the need for high-temperature deposition or complex substrate engineering, thereby offering a viable pathway for integration into thermally sensitive device platforms.