Metalorganic chemical vapor deposition of Al2O3 using trimethylaluminum and O2 precursors: Growth mechanism and crystallinity

Metalorganic chemical vapor deposition (MOCVD) of Al2O3 was studied by using trimethylaluminum and O2 precursors over a variety of temperature, flow, and pressure conditions. Growth within the low temperature region from 600 to 800 °C was found to be limited by a surface kinetic process that follows the Langmuir-Hinshelwood mechanism. In the high temperature region from 900 to 1050 °C, the growth process was influenced by prereactions in the gas phase. The crystallinity of MOCVD Al2O3 films grown in situ on GaN substrates was characterized by grazing incidence x-ray diffraction (GIXRD) and high-resolution transmission electron microscopy (HRTEM). GIXRD suggested that the Al2O3 films grown at 600 and 700 °C were amorphous, while those grown at 800, 900, 1000, and 1050 °C were crystalline with primarily γ-phase. HRTEM further showed that the γ-Al2O3 films grown at 900 and 1050 °C were poly and single crystalline, respectively. The crystal orientation relationships during the epitaxial growth of γ-Al2O3 on GaN at 1050 °C were also determined.