Electrical and optical properties of AlNxOy thin films deposited by reactive DC magnetron sputtering

Abstract

Aluminium, Al, is a metallic material used in a large variety of technological fields, such as surface plasmon-coupled emission (SPCE) devices for biochemical applications and it is also a good candidate to be used as nonresonante plasmonic nanoparticle in thin-film silicon solar cells. Aluminium nitride, AlN, is a semiconductor material and it can be used in the fabrication of optical sensors, LEDs, surface/bulk acoustic wave devices and in electronic packaging. Aluminium oxide, Al2O3, is an insulator material, used as protective film, as gate dielectric in flash memory circuits, OTFTs, MOSFET, etc. The AlOy system is also important in solar selective coatings since it exhibits very high solar selectivity. The possibility to associate the overall set of properties of the above mentioned base-materials might be the starting point for a material that may combine specific advantages of each of the three systems, Al, AlNx and AlOy, according to the particular requirements of a given application. In fact, the addition of small amounts of oxygen and nitrogen to a growing Al film can give rise to an oxynitride film with a wide range of different properties, where the optical and electrical ones may be tailored between those of the pure aluminium and those of aluminum nitride and oxide. In this work thin films of AlNxOy were prepared by reactive DC magnetron sputtering, using a pure Al target and an Ar/(N2,O2) gas mixture. Preliminary Transmission Electron Microscopy and EELS analysis suggested the growth of films with Al nanoparticles randomly embedded in an AlNxOy matrix. The particular structure, morphology and composition of the films induced a wide variation in the electrical properties, which can be explained using a tunnel barrier conduction mechanism for the electric charge transport through the films, as well as distinct optical responses, such as an unusual large broadband absorption for some films, with potential applications in solar cells and thermal photovoltaics.