Effect of Inhomogeneous Broadening in Ultraviolet III-Nitride Light-Emitting Diodes.

In the past years, light-emitting diodes (LED) made of GaN and its related ternary compounds with indium and aluminium have become an enabling technology in all areas of lighting. Visible LEDs have yet matured, but research on deep ultraviolet (UV) LEDs is still in progress. The polarisation in the anisotropic wurtzite lattice and the low free hole density in p-doped III-nitride compounds with high aluminium content make the design for high efficiency a critical step.

Gain and bandwidth of InP nanowire array photodetectors with embedded photogated InAsP quantum discs.

Here we report on the experimental results and advanced self-consistent real device simulations revealing a fundamental insight into the non-linear optical response of n-i-n InP nanowire array photoconductors to selective 980 nm excitation of 20 axially embedded InAsP quantum discs in each nanowire. The optical characteristics are interpreted in terms of a photogating mechanism that results from an electrostatic feedback from trapped charge on the electronic band structure of the nanowires, similar to the gate action in a field-effect transistor. From detailed analyses of the complex charge carrier dynamics in dark and under illumination was concluded that electrons are trapped in two acceptor states, located at 140 and 190 meV below the conduction band edge, at the interface between the nanowires and a radial insulating SiO cap layer.

Three-Dimensional Interfacing of Cells with Hierarchical Silicon Nano/Microstructures for Midinfrared Interrogation of In Situ Captured Proteins.

Label-free optical detection of biomolecules is currently limited by a lack of specificity rather than sensitivity. To exploit the much more characteristic refractive index dispersion in the mid-infrared (IR) regime, we have engineered three-dimensional IR-resonant silicon micropillar arrays (Si-MPAs) for protein sensing. By exploiting the unique hierarchical nano- and microstructured design of these Si-MPAs attained by CMOS-compatible silicon-based microfabrication processes, we achieved an optimized interrogation of surface protein binding.

Micromagnetic Simulations of Submicron Vortex Structures for the Detection of Superparamagnetic Labels.

We present a numerical investigation on the detection of superparamagnetic labels using a giant magnetoresistance (GMR) vortex structure. For this purpose, the Landau-Lifshitz-Gilbert equation was solved numerically applying an external z-field for the activation of the superparamagnetic label. Initially, the free layer's magnetization change due to the stray field of the label is simulated.

Ge(Sn) nano-island/Si heterostructure photodetectors with plasmonic antennas.

We report on photodetection in deep subwavelength Ge(Sn) nano-islands on Si nano-pillar substrates, in which self-aligned nano-antennas in the Al contact metal are used to enhance light absorption by means of local surface plasmon resonances. The impact of parameters such as substrate doping and device geometry on the measured responsivities are investigated and our experimental results are supported by simulations of the three-dimensional distribution of the electromagnetic fields. Comparatively high optical responsivities of about 0.

High Responsivity of InP/InAsP Nanowire Array Broadband Photodetectors Enhanced by Optical Gating.

High-performance photodetectors operating in the near-infrared (0.75-1.4 μm) and short-wave infrared (1.

Top-down GaN nanowire transistors with nearly zero gate hysteresis for parallel vertical electronics.

This paper reports on the direct qualitative and quantitative performance comparisons of the field-effect transistors (FETs) based on vertical gallium nitride nanowires (GaN NWs) with different NW numbers (i.e., 1-100) and diameters (i.

GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors.

Vertically aligned gallium nitride (GaN) nanowire (NW) arrays have attracted a lot of attention because of their potential for novel devices in the fields of optoelectronics and nanoelectronics. In this work, GaN NW arrays have been designed and fabricated by combining suitable nanomachining processes including dry and wet etching. After inductively coupled plasma dry reactive ion etching, the GaN NWs are subsequently treated in wet chemical etching using AZ400K developer (i.

CMOS-compatible optical switching concept based on strain-induced refractive-index tuning.

In this paper we present a planar lightwave switching mechanism based on large refractive index variations induced by electrically-driven strain control in a CMOS-compatible photonic platform. Feasibility of the proposed concept, having general validity, is numerically analyzed in a specific case-study given by a Mach-Zehnder Interferometer with Ge waveguides topped by a piezoelectric stressor. The stressor can be operated in order to dynamically tune the strain into the two interferometric arms.

Effect of Auger recombination and leakage on the droop in InGaN/GaN quantum well LEDs.

We investigate the effect of the epitaxial structure and the acceptor doping profile on the efficiency droop in InGaN/GaN LEDs by the physics based simulation of experimental internal quantum efficiency (IQE) characteristics. The device geometry is an integral part of our simulation approach. We demonstrate that even for single quantum well LEDs the droop depends critically on the acceptor doping profile.

A high efficiency dual-junction solar cell implemented as a nanowire array.

In this work, we present an innovative design of a dual-junction nanowire array solar cell. Using a dual-diameter nanowire structure, the solar spectrum is separated and absorbed in the core wire and the shell wire with respect to the wavelength. This solar cell provides high optical absorptivity over the entire spectrum due to an electromagnetic concentration effect.

InP nanowire array solar cells achieving 13.8% efficiency by exceeding the ray optics limit.

Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared with planar devices but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-type/intrinsic/n-type (p-i-n) doped InP nanowires and found that the nanowire diameter and the length of the top n-segment were critical for cell performance. Efficiencies up to 13.

Light absorption and emission in nanowire array solar cells.

Inorganic nanowires are under intense research for large scale solar power generation intended to ultimately contribute a substantial fraction to the overall power mix. Their unique feature is to allow different pathways for the light absorption and carrier transport. In this publication we investigate the properties of a nanowire array acting as a photonic device governed by wave-optical phenomena.