An insight into the epitaxial nanostructures of NiO and CeO2 thin film dielectrics for AlGaN/GaN heterostructures

Nickel oxide and cerium oxide thin films have been grown by metal-organic chemical vapor deposition on AlGaN/GaN heterostructures. Thin and epitaxial layers have been already obtained at low temperature (500 °C). Despite the two oxides possess the same crystal structure (face cubic centered compounds), different structural relationships have been observed with respect to the substrate. In particular, nickel oxide films were epitaxially grown along the <111> direction, while cerium oxide thin films showed <111> and <100> preferential orientations. These structural relationships have been justified by geometric and/or kinetics factors. In both cases, the epitaxial growth has been obtained at low temperature by the implementation of two second generation metal precursors, namely the nickel 2-thenoyl-trifluoroacetonate adduct with the tetramethylethylendiamine and cerium 1,1,1,5,5,5-hexafluoroacetlyacetonate adduct with bis(2-methoxyethyl) ether. Electrical characterization demonstrated that these films can be very promising as gate dielectrics for AlGaN/GaN transistors technology. In fact, the two oxide films showed really interesting electric properties such as dielectric constants (εNiO = 11.7 and εCeO2 = 26) close to the bulk values. Finally, it is noteworthy that among the widely used physical deposition methods, in this paper a chemical based deposition technique has been addressed for the epitaxial growth at low temperature of oxide thin films to be implemented in microelectronics applications.