Introduction

Gas and bio-chemical sensing is a crucial component in environmental monitoring applications, with requirements for emissions monitoring in a range of different situations; e.g. car exhausts, power stations, oil-rigs, coal mines, landfill sites, toxic/volatile chemicals detection at production facilities or disaster zones, and constituent control in pharmaceutical processing. High sensitivity optical gas detection requires reliable, cost-effective lasers emitting in the mid-infrared (2-5 μm) region tuned to the fundamental fingerprint absorptions of target gases which conveniently lie in this technologically important spectral range. But, although quantum cascade lasers have been successfully developed they are complex and prohibitively expensive. For many applications mid-infrared (MIR) LEDs are a far more attractive, cost-effective alternative especially for widespread distributed sensing applications requiring many point sensors. Compared with thermal sources LEDs are more robust, can be operated at high modulation rates and provide low power consumption better suited for portable instruments.

Alternatively, semiconductor surfaces can be functionalised to accept single molecular species which can then be selectively detected using optical (resonance) techniques. For situations e.g. bio-chemicals, which require high sensitivity detection, we shall adopt a parallel approach and exploit novel properties of semiconductor metamaterials based on recent work at UM2, who have demonstrated localized surface plasmon resonances (LSPRs) in periodic arrays of highly doped/un-doped InAsSb/GaSb semiconductor nanostructures.

Objectives:

• To advance the state-of-the-art in mid-IR LED sources for environmental gas sensing applications
• To provide new capabilities in high sensitivity environmental /bio-sensing using metamaterials

Partners involved in this Work Package

Collaborating partners: NOTT, UM2, ROME, SHEF, Tyndall-UCC, UCA, e2v, GSS, SIKÉMIA

Projects in this Work Package

Project 4.1: Growth and hydrogenation of Sb/N materials for high efficiency mid-IR LEDs in pollutant gas detection

Fellow:

Host: Lancaster University

To improve efficiency of MIR LEDs containing InAsSbN/InAs/AlAsSb QW and QD nanostructures at ULANC using hydrogenation, building on recent ~50x increase in InAsN PL at ROME. NOTT and Tyndall-UCC will provide input on band structure and carrier transport, while UCA will study defect formation and clustering. Also to increase optical extraction, using 2D hole arrays, plasmonic nanoparticles and/or resonant cavity designs to produce a narrow spectral emission for inexpensive, low power, compact light sources. SHEFF will provide assistance with processing. GSS and e2v will validate devices in a gas sensor context targeted on: CH4 (3.4 μm), HCl (3.55 μm), CO2 (4.0 μm), N2O (4.5 μm).

Project 4.2: Functionalised semiconductor metamaterials and plasmonics for high sensitivity chemical and bio-sensing

Fellow:

Host: University of Montpellier

To demonstrate localized surface plasmon resonances (LSPRs) in periodic arrays of highly doped/un-doped InAsSb/GaSb nanostructures, where highly doped InAsSb is degenerate and exhibits a metallic behaviour while being lattice-matched to GaSb. FDTD calculations will be performed to design the resonators. Reflectance spectroscopy will be used to establish the impact of the geometrical and physical properties of both InAsSb and GaSb on the LSPR. The metamaterials will be functionalised in collaboration with SIKEMIA. The target-structure is LSPR excitation in a waveguide configuration. Biochemical ligands will be anchored at the surface to bind the biomolecules under study. Sensitivity in the zeptamole range, i.e. ~1000 molecules, is envisaged.

Project 4.3: Electron transport in novel Mid-IR materials and devices

Fellow:

Host: University of Nottingham

This project will investigate the electron dynamics and scattering processes in InAsN by Hall effect, high electric field measurements and magneto-tunnelling spectroscopy (MTS). Pioneered at Nottingham MTS [Phys. Rev. Lett. (2003), Science 290, 124 (2000)], will be used to map the conduction band structure, particularly the resonant states induced by N, and to probe native donor defect states. We will use InAsN quantum well (QW) n-i-n and p-i-n double barrier resonant tunnel diodes and obtain an accurate description of the effect of N on the band structure and the design of novel tunnelling structures for the controlled injection and extraction of carriers in p-i-n diodes. This is relevant for the development of p-i-n diodes, targeted on key wavelengths, i.e. > 2μm.