Electrodeposited Ni/Ge and germanide schottky barriers for nanoelectronics applications

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Description/Abstract

In recent years metal/semiconductor Schottky barriers have found numerous applications in nanoelectronics. The work presented in this thesis focuses on the improvement of a few of the relevant devices using electrodeposition of metal on Ge for Schottky barrier fabrication. This low energy metallisation technique offers numerous advantages over the physical vapour deposition techniques. Electrical characteristics of the grown diodes show a high quality rectifying behaviour with extremely low leakage currents even on highly doped Ge. A non-Arrhenius behaviour of the temperature dependence is observed for the grown Ni/Ge diodes on lowly doped Ge that is explained by a spatial variation of the barrier heights. The inhomogeneity of the barrier hights is explained in line with an intrinsic surface states model for Ge. The understanding of the intrinsic surface states will help to create ohmic contacts for doped n-MOSFETs. NiGe were formed single phase by annealing. Results reveal that by using these high-quality germanide Schottky barriers as the source/drain, the subthreshold leakage currents of a Schottky barrier MOSFET could be minimised, in particular, due to the very low drain/body junction leakage current exhibited by the electrodeposited diodes. The Ni/Ge diodes on highly doped Ge show negative differential conductance at low temperature. This effect is attributed to the intervalley electron transfer in Ge conduction band to a low mobility valley. The results show experimentally that Schottky junctions could be used for hot electron injection in transferred-electron devices. A vertical Co/Ni/Si structure has been fabricated for spin injection and detection in Si. It is shown that the system functions electrically well although no magnetoresistance indicative of spin injection was observed.