Fabrication and analysis of ferromagnetic metallic films grown onto semiconductor substrates by electrochemical deposition.

摘要

The discovery of spin-dependent transport phenomena has spurred investigations of various material combinations involving ferromagnetic (FM) materials. The proposal of creating active spin-electronic three-terminal devices with transistor-like characteristics caused a wide interest in combinations of ferromagnetic materials with semiconductors (SC). Such devices would require the growth of epitaxial ferromagnetic layers with well-defined crystallographic magnetic and interface properties.; In this respect, electrochemical deposition (ECD) is a low-energy, room temperature deposition process, which is capable of growing high quality epitaxial layers.; In the present work, the author presents the structural and magnetic properties of Ni, Co, Fe and iron-rich FeNi films grown by ECD directly onto n-GaAs(001) and (011). In particular, the conditions upon which high quality, continuous films with defined magnetic properties at low thickness have been determined. For instance, epitaxial Ni films grown on GaAs(001) exhibited a sharp FM/SC interface after annealing at temperatures up to 250°C. In addition, successful electrodeposition of epitaxial Fe films on n-GaAs(001) and (011) has been achieved where the structural quality of the films depends on the composition of the plating solution.; Another attractive aspect of ECD is its capability to achieve selective growth of FM metallic features directly onto SC substrates without the need for mask fabrication. For instance, focused light beam illumination of SC substrates can induce metal film deposition at the illuminated regions. Similarly, upon application of a cathodic potential, the Schottky barrier formed at the SC substrate/electrolyte interface can be biased in the forward (reverse) direction for n-type SC (p-type SC), leading to selective electron transfer from a n-type SC while breakdown of the Schottky barrier would be necessary for deposition on a p-type substrate. The process will thus be spatially selective on a lateral modulation of the substrate doping.; In this respect, the author presents experimental results to elucidate the electroless growth of Cu structures from CUSO4 based solutions on p-Si upon laser illumination. Additionally, the author demonstrates the selective electrodeposition of ferromagnetic Co on p/n doping patterns in a GaAs and a Si surface where patterns were created by chemical etching (GaAs) and ion-implantation ( p-Si).