Nano-silicide formation through point contact reaction, nickel-silicon/silicon/nickel-silicon and platinum-silicon/silicon/platinum-silicon nanowire heterostructures for nanodevices

Nanowire heterostructures of NiSi/Si/NiSi and PtSi/Si/PtSi are investivagted as building blocks for field-effect transistors where the source-drain contacts are defined by metallic silicide nanowire regions. Nano-heterostructures of NiSi/Si/NiSi, in which the length of the Si region can be controlled down to 2 nm, have been produced using in-situ point contact reaction between Si and Ni nanowires in an ultra-high vacuum transmission electron microscope. The Si region was found to be highly strained, more than 12%. The strain increases with the decreasing Si layer thickness and can be controlled by varying heating temperature. It was observed that the Si nanowire is transformed into a bamboo-type grain of single crystal NiSi from both ends following the path with low activation energy. We propose the reaction is assisted by interstitial diffusion of Ni atoms within the Si nanowire and is limited by the rate of dissolution of Ni into Si at the point contact interface. The rate of incorporation of Ni atoms to support the growth of NiSi has been measured to be 7 x 10 -4 sec per Ni atom. The nanoscale epitaxial growth rate of single-crystal NiSi has been measured using high resolution lattice imaging videos. Based on the rate, we can control the consumption of Si and, in turn, the dimensions of the nano-heterostructure down to less than 2 nm, thereby far exceeding the limit of conventional patterning process. The controlled huge strain in the controlled atomic scale Si region, potential gate of Si-nanowire-based transistors, is expected to significantly impact the performance of electronic devices.;Also, we report a method of fabrication of high quality multiple heterostructures of NiSi/Si in a nanowire of Si and investigation of NiSi formation in nano-scale. By using the point contact reaction between several Ni nanodots and a Si nanowire carried out in-situ in an ultrahigh vacuum transmission electron microscopy, multiple sections of single-crystal NiSi and Si with very sharp interfaces were produced in a Si nanowire. Owing to the supply-limited point contact reaction, we propose that the nucleation and growth of the bamboo-type NiSi grains start at the middle of the point contacts between two Ni nanodots and a Si nanowire. The reaction happens by the dissolution of Ni into the Si nanowire at the point contacts and by interstitial diffusion of Ni atoms within a Si nanowire. The growth of NiSi stops as the amount of Ni in the Ni nanodots is consumed. The fabricated multi-nano-heterostructures may enhance the development of circuit elements in nano-scale electronic devices.;Additionally, the formation of PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices from such heterostructures are demonstrated. Scanning electron microscopy studies show that silicon nanowires can be converted into PtSi nanowires through controlled reactions between lithographically defined platinum pads and silicon nanowires. High-resolution transmission electron microscopy studies show that PtSi/Si/PtSi heteorstructure has an atomically sharp interface with epitaxial relationships of Si [1-10]//PtSi [010] and Si (111)//PtSi (101). Electrical measurements show that the pure PtSi nanowires have low resistivities ∼28.6 muO·cm and high breakdown current densities >1 x 108 A/cm 2. Furthermore, using single crystal PtSi/Si/PtSi nanowire heterostructures with atomically sharp interfaces, we have fabricated high-performance nanoscale field-effect transistors from intrinsic silicon nanowires, in which the source and drain contacts are defined by the metallic PtSi nanowire regions, and the gate length is defined by the Si nanowire region. Electrical measurements show nearly perfect p-channel enhancement mode transistor behavior with a normalized transconductance of 0.3 mS/mum, field-effect hole mibility of 168 cm2/V·s, and on/off ratio >10 7, demonstrating the best performing device from intrinsic silicon nanowires.