Surfaces and interfaces characterization for the development of diamond power electronic devices

Abstract

The management of electric energy is one of the more important challenges of humanity with increasing energy demands. High power elements in the electric grid such as rectifiers are currently based on silicon. Design of new architectures has kept silicon-based devices on top of the high-power devices market. However, the inherent limitations of silicon have lead researchers to explore other semiconductor candidates. Diamond superior electronic and thermal properties make it a promising candidate for its application in high-power and high-frequency regime. For this reason, diamond has generated great interest to researchers in the last decades. The new methods of diamond synthesis fostered and opened research towards this new technology. As a wide band-gap semiconductor, diamond insulating nature makes its electronic application very dependent on scientific and technologic aspects such as doping, surface and interface phenomena as well as other device manufacturing process implications. Therefore, success in defining the ultimate performance of diamond electronic devices will require a thorough examination of the most relevant electronic aspects in them, in order to understand their origins and take control over the consequences. This thesis is framed on the surface and interface aspects of (100) diamond for its application in electronic devices. It is first focused on one of the most accepted concepts on diamond electronics: the relevance of diamond surface terminations for the definition of the device performance. The use of the angle-resolved X-ray photoelectron spectroscopy (ARXPS) mode has prompted the reinterpretation of the electronic contributions near the surface and has allowed opening the discussion on the origin of surface p-type conduction of the hydrogenated surface. Regarding oxygen termination, the ARXPS results have served as a starting platform for new models of surface reconstruction that go through the consideration of sp2 hybridizations, breaking with the strongly rooted conception of ideal full-sp3 surface reconstruction. On the other hand, interface aspects are discussed in the frame of metal-diamond junctions, which is the base structure for ohmic and Schottky contacts. The metal-diamond reaction has been linked to the low thermal stability of the contact and the deterioration of its electronic behaviour. To avoid this reaction, some researchers have chosen a preformed carbide with a metallic character such as WC, showing high thermal stability and a close to ideal Schottky behaviour. The comprehensive interface nanoscopic characterization allows this thesis to put into perspective its phenomenology in such Schottky structures with that of other options. The results of this thesis will help to better understand and continue the debate on some of the fundamental scientific aspects of diamond-based electronic devices.