Ameya Bapat

Plasma synthesis of single-crystal silicon nanoparticles for novel electronic device applications

Single-crystal nanoparticles of silicon, several tens of nanometres in diameter, may be suitable as building blocks for single-nanoparticle electronic devices. Previous studies of nanoparticles produced in low-pressure plasmas have demonstrated the synthesis of nanocrystals 2–10 nm diameter but larger particles were amorphous or polycrystalline. This work reports the use of a constricted, filamentary capacitively coupled low-pressure plasma to produce single-crystal silicon nanoparticles with diameters between 20 and 80 nm. Particles are highly oriented with predominantly cubic shape. The particle size distribution is rather monodisperse. Electron microscopy studies confirm that the nanoparticles are highly oriented diamond-cubic silicon.

Synthesis of highly oriented, single-crystal silicon nanoparticles in a low-pressure, inductively coupled plasma

Single-crystal nanoparticles of silicon, several tens of nm in diameter, may be suitable as building blocks for single-nanoparticle electronic devices. Previous studies of nanoparticles produced in low-pressure plasmas have demonstrated the synthesis nanocrystals of 2–10 nm diameter but larger particles were amorphous or polycrystalline. This work reports the use of an inductively coupled low-pressure plasma to produce single-crystal silicon nanoparticles with diameters between 20 and 80 nm. Electron microscopy studies confirm that the nanoparticles are highly oriented diamond-cubic silicon.

A plasma process for the synthesis of cubic-shaped silicon nanocrystals for nanoelectronic devices

Low pressure silane plasmas are known for their ability to synthesize silicon nanoparticles via gas phase nucleation. While in the past this particle formation has often been considered from the viewpoint of a contamination problem in semiconductor processing, we here describe a silane low pressure plasma that enables the synthesis of highly oriented, cubic-shaped silicon nanocrystals with a rather monodisperse size distribution. These silicon nanocubes have successfully been used in the manufacture of single nanoparticle vertical transistors. We discuss the advantages of this new paradigm of building nanoelectronic devices. The plasma synthesis process is characterized in more detail than in prior work. The particle nucleation, growth and shape evolution are studied. Results indicate that the process provides two spatially distinct zones: a diffuse plasma for particle growth and a constricted plasma zone for particle annealing. Measurements of the plasma ion density using a capacitive probe suggest that the plasma density in the constricted region of the plasma is about an order of magnitude higher than in the diffuse region, likely aiding the formation of cubic silicon nanocrystals. The process of particle extraction from the plasma reactor is discussed based on the balance of various forces acting on the particles. It is found that the use of a critical orifice for particle extraction enables the detrapping of particles which carry as many as 35 elementary charges.

Generation of nano-sized free standing single crystal silicon particles

A system has been designed to generate monodisperse, single crystal silicon nanoparticles. The particles are generated using a SiH4/H2 mixture in a high density plasma. An aerodynamic lens assembly focuses and size selects the particles. A high voltage plate is used to accelerate the charged particles such that they can be injected into a high temperature annealing tube to be heated. The shape and structure of the particles are changed in the annealing tube. Single crystals are obtained.

Microscopy of nanoparticles for semiconductor devices

The miniaturization of semiconductor devices brings the impending need for nanoscale components for which nanoparticles of semiconductor materials are uniquely suited. However, their small length scales are known to produce properties unique from those of their bulk form. Full characterization of the nanoparticles suggested for use in devices becomes imperative. This study investigates silicon nanocubes prepared by a constricted-mode capacitive silane-argon plasma. These cubes have been proposed as key components in nanoscale transistors. Various techniques are used to examine these particles and their implementation in a potential device is explored.

A single nanoparticle silicon transistor

Unlike devices built using wafers, single nanoparticle semiconductor devices made from singlecrystal particles would allow the construction of high performance three-dimensional circuits and the integration of otherwise chemically and structurally incompatible single-crystal materials on virtually any substrate. This would dramatically reduce interconnect delay in integrated circuits, eliminate substrate parasitic effects, and allow the monolithic integration of complex systems.

Synthesis of Crystalline Silicon Nanoparticles in Low-Pressure Inductive Plasmas

Amorphous silicon has been used for a wide variety of electronic applications including thin film transistors and energy conversion devices. However, these devices suffer greatly from defect scattering and recombination. A method for depositing crystalline silicon would be highly desirable, especially if it can be remotely created and deposited on any kind of substrate. Our work aims at synthesis and deposition of mono-disperse, single crystal silicon nanoparticles, several tens of nm in diameter on varied substrates. Synthesis of nanocrystals of 2–10 nm diameter has been previously reported but larger particles were amorphous or polycrystalline. This work reports the use of an inductively coupled low-pressure plasma to produce nanocrystals with diameters between 20–80 nm. Electron microscopy studies confirm that the nanocrystals are highly oriented diamond-cubic silicon.

Nanoparticles: A Route to Post-Shrink Information Systems

Single crystal semiconductor nanoparticles provide a novel path to monolithic integration of lattice mismatched and even chemically incompatible materials. This in turn provides an avenue to reliable, high performance, integrated information systems that go well beyond todays integrated circuits. This paper reviews aspects of this work including single crystal silicon nanoparticle transistors and full-spectrum silicon quantum dots as light emitting structures.

Single nanoparticle semiconductor devices

Using a new technique in forming the cubic single-crystal silicon nanoparticles that are about 40 nm on a side, the authors have demonstrated a vertical-flow surround-gate Schottky-barrier transistor. This approach allows the use of well-known approaches to surface passivation and contact formation within the context of deposited single-crystal materials for device applications. It opens the door to the novel three-dimensional integrated circuits and new approaches to hyper integration. The fabrication process involves successive deposition and planarization and does not require nonoptical lithography. Device characteristics show reasonable turn-off characteristics and on-current densities of more than 107 A/cm2