Electronic properties of gold nanoclusters/semiconductor structures with low resistance interfaces

Self-assembled metal/molecule/semiconductor nanostructures are utilized to define nanoelectronic device contact structures and are characterized using ultra high vacuum (UHV) scanning tunneling microscopy (STM).; As examples of the controlled nanostructures for nanoelectronic device applications, nonalloyed ohmic contact nanostructures have been utilized on a surface layer of LTG:GaAs, i.e., GaAs grown at a low temperature by molecular beam epitaxy. The controlled-geometry nanocontact is obtained by depositing a 4 nm diameter single crystal Au cluster (truncated octahedral shape) onto n-GaAs(100) having LTG:GaAs based ohmic contact layers using ex-situ chemical self-assembly techniques. A self-assembled monolayer (SAM) of xylyl dithiol (HS-CH2-C6H4-CH2-SH) is formed on LTG:GaAs and provides an effective organic metal/semiconductor interface having both a robust mechanical tethering and a strong electronic coupling between the Au nanoclusters and the LTG:GaAs surface.; UHV STM is used to locate and probe the electronic properties of the nanocontacts. STM current versus voltage (I-V) data measured over Au nanoclusters exhibit an ohmic behavior with a significant enhancement in the conduction for low bias voltages compared to I-V data over the SAM-coated LTG:GaAs substrate. A specific contact resistance of 10 -6--10-7 O·cm 2 and a current density of 106--107 A/cm2 have been measured on the nanocontacts from STM. The ohmic nanocontact is mainly due to the sequential tunneling through the xylyl dithiol layer and the LTG:GaAs layer while a midgap band of defect states in the LTG:GaAs layer assists conduction as if it effectively reduces the barrier width.; Another interesting approach is to combine the nanoscale elements (Au clusters) and ordering from self-assembly processes with a procedure which can impose an arbitrary larger-scale pattern to form the specific configurations and interconnections needed for computation. Toward this goal, high-quality hexagonal close-packed arrays of Au nanoclusters (5 nm in diameter) are formed within patterned regions on active GaAs substrates having LTG: GaAs cap layer and are characterized using STM. This approach utilizes a patterned template which guides Au nanoclusters into pre-selected regions with xylyl dithiol. The directed self-assembly techniques used to fabricate these structures have the potential to provide high-throughput fabrication of nanostructures for nanoelectronics and other nanoscale applications.