Nanohole array surface plasmon resonance (SPR) sensors offer a promising platform for high-throughput label-free biosensing. Integrating nanohole arrays with group-IV semiconductor photodetectors could enable low-cost and disposable biosensors compatible to Si-based complementary metal oxide semiconductor (CMOS) technology that can be combined with integrated circuitry for continuous monitoring of biosamples and fast sensor data processing. Such an integrated biosensor could be realized by structuring a nanohole array in the contact metal layer of a photodetector. We used Fouriertransform infrared spectroscopy to investigate nanohole arrays in a 100 nm Al film deposited on top of a vertical Si-Ge photodiode structure grown by molecular beam epitaxy (MBE). We find that the presence of a protein bilayer, constitute of protein AG and Immunoglobulin G (IgG), leads to a wavelength-dependent absorptance enhancement of ~ 8 %.
The fabrication and characterization of a compact InP-based polarization beamsplitter (PBS) is presented. A multimode interference (MMI) coupler with an internal air hole photonic crystal (PhC) section is utilized to separate the two polarizations. The PhC structure in the middle of the MMI is polarization dependent, so that one polarization is reflected and the other one is transmitted; both are collected by the respective output ports of the MMI coupler. The obtained experimental results show that the PBS as short as ~400 µm has an extinction ratio as large as 15 dB.
In this work variations of the carrier lifetime in a GaInAsP/InP quantum well in two-dimensional PhC structures etched
by Ar/Cl<sub>2</sub> chemically assisted ion beam etching as a function of the processing parameters is investigated. It is shown
that the deposition conditions of the SiO<sub>2</sub> mask material and its coverage as well as other process steps such as annealing
affect the carrier lifetimes. However the impact of patterning the semiconductor on the carrier lifetime is dominant,
showing over an order of magnitude reduction. For given PhC lattice parameters, the sidewall damage is shown to be
directly related to the measured carrier lifetimes. A simple qualitative model based on sputtering theory and assuming a
conical hole-shape development during etching is used to explain the experimental results.
This work addresses feature size effects (the lag-effect and roughness development) in chemically assisted ion beam etching (CAIBE) etching of InP based photonic crystals. Photonic crystal fields with varying hole size and periods were etched with different etching times. The slope of the etch depth versus diameter curves (lag-curves) reveals a hole size dependence, with a critical aspect ratio higher than 25. A model for the etch rate specific to Ar/Cl<sub>2</sub> CAIBE is proposed. We calculate the etch rate using a physico-chemical model which takes in to account the effect of Ar-ion sputtering and surface chemical reactions. In addition, it combines the aspect ratio dependence of the gas conductance of the etched holes. The origin and evolution of the bottom roughness of the etched holes is examined. The impact of the feature size dependence of the etching on the photonic crystal optical properties is then assessed by measuring the quality-factor of one dimensional Fabry Perot cavities using the Internal Light Source method, and discussed in terms of hole shape and depth. A systematic trend between the determined quality factor (Q) and the lag-effect is evidenced: Q decreases from about 250 to 60 when the hole depth drops from 5 μm to 2 μm.
This work investigates the current transport across two-dimensional PhCs dry etched into InP-based low-index-contrast
vertical structures using Ar/Cl<sub>2</sub> chemically assisted ion beam etching. The electrical conduction through the PhC field is
influenced by the surface potential at the hole sidewalls, which is modified by dry etching. The measured current-voltage
(I-V) characteristics are linear before but show a current saturation at higher voltages. This behaviour is confirmed by
simulations performed by ISE-TCAD software. We investigate the dependence of the conductance of the PhC area as a
function of the geometry of the photonic crystal as well as the material parameters. By comparing the experimental and
simulated conductance of the PhC, we deduce that the Fermi level is pinned at 0.1 eV below the conduction band edge.
The method presented here can be used for evaluating etching processes and surface passivation methods. It is also
applicable for other material systems and sheds new light on current driven PhC tuning.
One of the most distinctive features of photonic crystals (PhCs) is their unique wavelength dispersion allowing novel device concepts for enhancement of photonic functionality and performance. Here, we present examples of our design and demonstrations utilizing dispersion properties of 1D and 2D photonic crystals. This includes the demonstration of negative refraction in 2D PhC at optical wavelengths, filters based on 1D and 2D PhC waveguides, and the design of a widely tunable filter involving 1D PhC.
The coupling efficiency between external plane waves and the Bloch waves in photonic crystals are investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air <i>n</i>=1 and a photonic crystal with effective index -1. It is also shown that, for point imaging by a photonic crystal slab owing to the negative refraction, the influence of the surface termination to the transmission and the imaging quality is significant. Finally, we present results demonstrating experimentally negative refraction in a two-dimensional photonic crystal.