Physical mechanism of surface roughening of the radial Ge-core/Si-shell nanowire heterostructure and thermodynamic prediction of surface stability of the InAs-core/GaAs-shell nanowire structure

Nanowire Electronics: From Nanoscale to Macroscale

Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.

An analytical model for the bending of radial nanowire heterostructures

The balance between surface energy and elastic strain energy determines the bending induced by heteroepitaxial growth on the surface of thin nanowires.

Modification of Stranski-Krastanov growth on the surface of nanowires

The heteroepitaxial growth of strained islands on a planar substrate offers an attractive route to the fabrication of quantum dots (QDs). To obtain more functions and superior properties, recent efforts have focused on using nanowires (NWs) as substrates to produce attractive structures that combine QDs with NWs. As the lateral size of an NW is large, it is possible that islands are formed on the side walls of the NW. However, no islands exist, and the lateral surface is rather smooth in thin, core-shell NWs. The existing theoretical models on the growth on planar and patterned substrates are not appropriate for the growth transition on the surface with nanoscale curvature. We thus urgently need to understand the basic physics involved in the strain-induced growth on the surface with nanoscale curvature. Here, we established a theoretical model to study the strain-induced growth on the surface, which showed that the Stranski-Krastanov (SK) mode can change to the Frank-van der Merwe (FM) mode due to the limit of the surface to the island's lateral growth. Using the model to investigate the heterostructured core/shell nanowires (NWs), we found, in addition to the SK mode on thick NWs and the FM mode on thin NWs, that there is a multiplex mode on medium NWs which includes the initial layer growth, the intermediate islands' growth and the final layer growth again. The established theoretical model not only explained some puzzling experimental results but also provided useful information to design and control the epitaxial growth on the surface with nanoscale curvature.

Understanding quantum confinement in nanowires: basics, applications and possible laws

A comprehensive investigation of quantum confinement in nanowires has been carried out. Though applied to silicon nanowires (SiNWs), it is general and applicable to all nanowires. Fundamentals and applications of quantum confinement in nanowires and possible laws obeyed by these nanowires, have been investigated. These laws may serve as backbones of nanowire science and technology. The relationship between energy band gap and nanowire diameter has been studied. This relationship appears to be universal. A thorough review indicates that the first principles results for quantum confinement vary widely. The possible cause of this variation has been examined. Surface passivation and surface reconstruction of nanowires have been elucidated. It has been found that quantum confinement owes its origin to surface strain resulting from surface passivation and surface reconstruction and hence thin nanowires may actually be crystalline-core/amorphous-shell (c-Si/a-Si) nanowires. Experimental data available in the literature corroborate with the suggestion. The study also reveals an intrinsic relationship between quantum confinement and the surface amorphicity of nanowires. It demonstrates that surface amorphicity may be an important tool to investigate the electronic, optoelectronic and sensorial properties of quantum-confined nanowires.