Semiconductor nanowires show promise for use in nanoelectronics, fundamental electron transport studies, quantum optics and biological sensing. Such applications require a high degree of nanowire growth control, right down to the atomic level. However, many binary semiconductor nanowires exhibit a high density of randomly distributed twin defects and stacking faults, which results in an uncontrolled, or polytypic, crystal structure. Here, we demonstrate full control of the crystal structure of InAs nanowires by varying nanowire diameter and growth temperature. By selectively tuning the crystal structure, we fabricate highly reproducible polytypic and twin-plane superlattices within single nanowires. In addition to reducing defect densities, this level of control could lead to bandgap engineering and novel electronic behaviour.

http://www.dstuns.iitm.ac.in/grouppresentations/2009/Controlled%20Polytypic%20and%20twin-plae%20superlattics.pdf

Controlled polytypic and twin-plane superlattices in iii-v nanowires.

Experimental and theoretical progress toward quantum computation with spins in quantum dots (QDs) is reviewed, with particular focus on QDs formed in GaAs heterostructures, on nanowire-based QDs, and on self-assembled QDs. We report on a remarkable evolution of the field, where decoherence—one of the main challenges for realizing quantum computers—no longer seems to be the stumbling block it had originally been considered. General concepts, relevant quantities, and basic requirements for spin-based quantum computing are explained; opportunities and challenges of spin-orbit interaction and nuclear spins are reviewed. We discuss recent achievements, present current theoretical proposals, and make several suggestions for further experiments.

Prospects for Spin-Based Quantum Computing in Quantum Dots

Synthesis forms a vital aspect of the science of nanomaterials. In this context, chemical methods have proved to be more effective and versatile than physical methods and have therefore, been employed widely to synthesize a variety of nanomaterials, including zero-dimensional nanocrystals, one-dimensional nanowires and nanotubes as well as two-dimensional nanofilms and nanowalls. Chemical synthesis of inorganic nanomaterials has been pursued vigorously in the last few years and in this article we provide a perspective on the present status of the subject. The article includes a discussion of nanocrystals and nanowires of metals, oxides, chalcogenides and pnictides. In addition, inorganic nanotubes and nanowalls have been reviewed. Some aspects of core–shell particles, oriented attachment and the use of liquid–liquid interfaces are also presented.

https://www.bibalex.org/CSSP/papers/Attachments/Dalton_review.pdf

Synthesis of inorganic nanomaterials

A review of nanowire growth promoted by alloys and non-alloying elements with emphasis on Au-assisted III-V nanowires

There are a variety of methods for synthesizing or fabricating one-dimensional (1D) nanostructures containing heterojunctions between different materials. Here we review recent developments in the synthesis and fabrication of heterojunctions formed between different materials within the same 1D nanostructure or between different 1D nanostructures composed of different materials. Structures containing 1D nanoscale heterojunctions exhibit interesting chemistry as well as size, shape, and material-dependent properties that are unique when compared to single-component materials. This leads to new or enhanced properties or multifunctionality useful for a variety of applications in electronics, photonics, catalysis, and sensing, for example. This review separates the methods into vapor-phase synthesis, solution-phase synthesis, template-based synthesis, and other approaches, such as lithography, electrospinning, and assembly. These methods are used to form a variety of heterojunctions, including segmented, core/shell, branched, or crossed, from different combinations of semiconductor, metal, carbon, and polymeric materials.

The synthesis and fabrication of one-dimensional nanoscale heterojunctions.

We present the growth of homogeneous InAs1-xPx nanowires as well as InAs1-xPx heterostructure segments in InAs nanowires with P concentrations varying from 22% to 100%. The incorporation of P has been studied as a function of TBP/TBAs ratio, temperature, and diameter of the wires. The crystal structure of the InAs as well as the InAs1-xPx segments were found to be wurtzite as determined from high-resolution transmission electron microscopy. Furthermore, temperature-dependent electrical transport measurements were performed on individual heterostructured wires to extract the conduction band offset of InAs1-xPx relative to InAs as a function of composition. From these measurements we extract a value of the linear coefficient of the conduction band versus x of 0.6 eV and a nonlinear coefficient, or bowing parameter, of 0.2 eV. Finally, homogeneous InAs0.8P0.2 nanowires were shown to have a nondegenerate n-type doping and function as field-effect transistors at room temperature. (Less)

InAs1-xPx nanowires for device engineering.

The development of photovoltaics as a serious means of producing renewable energy has accelerated greatly in the last ten years, with prices for silicon-based solar cell systems dropping dramatically in the last few years. The next great opportunity for photovoltaics following this competitiveness in prices will be to enhance the cell and panel efficiencies. It is quite generally seen that the most viable platform on which this should be realized will be as augmented silicon solar cells, in which a top cell will be combined with the silicon bottom cell in a tandem configuration, by which the efficiency can be enhanced by a factor from 20% to 50%, depending on details of the approach. In this paper, we report on the status of one such approach, namely, with a top cell comprising III–V nanowires, connected to the bottom silicon cell in a two-terminal or four-terminal configuration. Among the most important opportunities, we show that a substrate-free growth, called Aerotaxy, offers a radical reduction in the total price picture. Besides the description of the key technical approaches, we also discuss the environmental issues.

/pdf/towards-nanowire-tandem-junction-solar-cells-on-silicon-43tet6jn7y.pdf

Towards Nanowire Tandem Junction Solar Cells on Silicon

We report recent progress toward on-chip single photon emission and detection in the near infrared utilizing semiconductor nanowires. Our single photon emitter is based on a single InAsP quantum dot embedded in a p-n junction defined along the growth axis of an InP nanowire. Under forward bias, light is emitted from the single quantum dot by electrical injection of electrons and holes. The optical quality of the quantum dot emission is shown to improve when surrounding the dot material by a small intrinsic section of InP. Finally, we report large multiplication factors in excess of 1000 from a single Si nanowire avalanche photodiode comprised of p-doped, intrinsic, and n-doped sections. The large multiplication factor obtained from a single Si nanowire opens up the possibility to detect a single photon at the nanoscale.

/pdf/single-photon-emission-and-detection-at-the-nanoscale-4z1waup049.pdf

Single photon emission and detection at the nanoscale utilizing semiconductor nanowires

/pdf/single-photon-emission-and-detection-at-the-nanoscale-3byx3mrad7.pdf

Mikael Björk

Papers

InAs1-xPx nanowires for device engineering.

Towards Nanowire Tandem Junction Solar Cells on Silicon

Single photon emission and detection at the nanoscale utilizing semiconductor nanowires

Single photon emission and detection at the nanoscale utilizing semiconductor nanowires