In-situ thermal cleaning of the sapphire substrate and temperature effect on epitaxial AlN

Abstract

The impact of thermal surface cleaning on epitaxial AlN thin films grown on sapphire is investigated in this study at various temperatures. The sapphire substrate is cleaned in a hydrogen environment. Structural, optical, and surface morphology properties of the samples are investigated by using high-resolution X-ray diffraction, Raman spectroscopy, UV–visible spectroscopy, and atomic force microscopy, respectively. Because wastes from the surface of sapphire, which begins to decompose after 1200 °C, cannot be entirely removed at such a low temperature, grain distribution and grain size in the nucleation layer are impacted. Moreover, when a sapphire is cleaned at a high temperature, the rate of breakdown of oxygen atoms from the surface rises, and islands appear on the surface. Roughnesses on the sapphire surface cause misoriented grains and deteriorated the structure. The surface of the sapphire, which is cleaned at 1245 °C, was both sufficiently cleaned and not etched too much, uniformly distributed, and large-sized particles formed in the nucleation layer. Thus, the AlN thin film has grown with high quality in terms of structure, optics, and surface. Experimental results have demonstrated that the in-situ thermal cleaning temperature has a critical influence on the properties of the AlN.