Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

In this perspective, we take a critical look at the research progress within the nanowire community for the past decade We discuss issues on the discovery of fundamentally new phenomena versus performance benchmarking for many of the nanowire applications We also notice that both the bottom-up and top-down approaches have played important roles in advancing our fundamental understanding of this new class of nanostructures Finally we attempt to look into the future and offer our personal opinions on what the future trends will be in nanowire research

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Semiconductor nanowire: what's next?

The manipulation of optical energy in structures smaller than the wavelength of light is key to the development of integrated photonic devices for computing, communications and sensing. Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e. waveguiding). Combined with optical gain, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires with favorable resonant feedback. We have further explored the properties and functions of individual ultralong crystalline oxide nanoribbons that act as subwavelength optical waveguides, nonlinear frequency converter and assess their applicability as nanoscale photonic elements and scanning probes. Semiconductor nanowires offer a versatile photonic platform due to the ability to specify material size, shape, and composition. The integration of multiple unique materials with distinct optical properties promises to enable advances for several applications ranging from solid state lighting, biochemical sensing to imaging and spectroscopy.

http://ieeexplore.ieee.org/iel5/4302825/4302826/04302854.pdf

Nanowire Photonics

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.

In most superconductors, the pairing-up of electrons responsible for resistance-free conductivity is driven by vibrations of the solid's crystal lattice. But there are other superconducting materials in which the 'glue' responsible for binding electrons is thought to have a very different origin: quantum fluctuations of spin or charge. An unusually 'violent' generalization of such a pairing mechanisms, in which spin and charge instabilities combine forces, has been identified in the unconventional superconductor CeRhIn5. These intimately coupled fluctuations significantly disrupt the flow of electrons in their normal unpaired state, yet also provide the quantum-mechanical glue necessary for generating superconducting pairs. In this paper, the crystal structure and stacking fault density of semiconducting nanowires composed of the same material are controlled by doping, leading to twinning superlattices. Periodic arrays of rotational dislocations lead to crystal heterostructures in indium phosphide and gallium phosphide nanowires. Semiconducting nanowires offer the possibility of nearly unlimited complex bottom-up design1,2, which allows for new device concepts3,4. However, essential parameters that determine the electronic quality of the wires, and which have not been controlled yet for the III–V compound semiconductors, are the wire crystal structure and the stacking fault density5. In addition, a significant feature would be to have a constant spacing between rotational twins in the wires such that a twinning superlattice is formed, as this is predicted to induce a direct bandgap in normally indirect bandgap semiconductors6,7, such as silicon and gallium phosphide. Optically active versions of these technologically relevant semiconductors could have a significant impact on the electronics8 and optics9 industry. Here we show first that we can control the crystal structure of indium phosphide (InP) nanowires by using impurity dopants. We have found that zinc decreases the activation barrier for two-dimensional nucleation growth of zinc-blende InP and therefore promotes crystallization of the InP nanowires in the zinc-blende, instead of the commonly found wurtzite, crystal structure10. More importantly, we then demonstrate that we can, once we have enforced the zinc-blende crystal structure, induce twinning superlattices with long-range order in InP nanowires. We can tune the spacing of the superlattices by changing the wire diameter and the zinc concentration, and we present a model based on the distortion of the catalyst droplet in response to the evolution of the cross-sectional shape of the nanowires to quantitatively explain the formation of the periodic twinning.

Twinning superlattices in indium phosphide nanowires

We report reproducible fabrication of InP−InAsP nanowire light-emitting diodes in which electron−hole recombination is restricted to a quantum-dot-sized InAsP section. The nanowire geometry naturally self-aligns the quantum dot with the n-InP and p-InP ends of the wire, making these devices promising candidates for electrically driven quantum optics experiments. We have investigated the operation of these nanoLEDs with a consistent series of experiments at room temperature and at 10 K, demonstrating the potential of this system for single photon applications.

Single quantum dot nanowire LEDs.

We show the epitaxial integration of III–V semiconductor nanowires with silicon technology. The wires are grown by the VLS mechanism with laser ablation as well as metal–organic vapour phase epitaxy. The hetero-epitaxial growth of the III– Vn anowires on silicon was confirmed with x-ray diffraction pole figures and cross-sectional transmission electron microscopy. We show preliminary results of two-terminal electrical measurements of III–V nanowires grown on silicon. E-beam lithography was used to predefine the position of the nanowires. (Some figures in this article are in colour only in the electronic version)

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Position-controlled epitaxial III?V nanowires on silicon

The invention describes a tunable filter arrangement with a plurality of resonators which are coupled to one another and of which there is at least one which comprises a piezoelectric component made of a ferroelectric material and to which a DC voltage source is connected. The application of a DC voltage to the resonator renders it possible to change its electrical properties and thus the overall filter characteristic. Furthermore, a transmitter, a receiver device, and a mobile telephone device with such a filter arrangement are disclosed, aswell as a tunable bulk acoustic wave resonator.

Tunable filter arrangement comprising resonators with reflection layers

A MEMS pressure sensor wherein at least one of the electrode arrangements comprises an inner electrode and an outer electrode arranged around the inner electrode. The capacitances associated with the inner electrode and the outer electrode are independently measured and can be differentially measured. This arrangement enables various different read out schemes to be implemented and also enables improved compensation for variations between devices or changes in device characteristics over time.

MEMS capacitive pressure sensor, operating method and manufacturing method

The invention describes a tunable filter arrangement with at least two resonators which are coupled to one another and of which at least one is connected to a capacitor with tunable capacitance. The electrical properties of the resonator, and thus the overall filter characteristic, can be changed through a change in the capacitance of the capacitor. Furthermore, a transmitter, a receiver, a mobile telephone device, and a wireless data transmission system comprising such a filter arrangement are disclosed, as is a tunable bulk acoustic wave resonator.

Olaf Wunnicke

Papers

Single quantum dot nanowire LEDs.

Position-controlled epitaxial III?V nanowires on silicon

Tunable filter arrangement comprising resonators with reflection layers

MEMS capacitive pressure sensor, operating method and manufacturing method

Tunable filter arrangement