Quantum Dot Lasers (1.3 m) Low J th achieved but T 0 remains finite around RT High T 0 in p-doped QDs at expense of higher J th T 0 in all p-doped lasers is dropping down K just above 60 o C Our results show this is due to: changes in carrier confinement and transport due Columbic attraction of extra holes a decrease of J th with increasing T until thermal equilibrium point together with increasing Auger process explain high T 0 in the p-doped QD lasers Nicolas Masse, Igor Marko, Stephen Sweeney, Alf Adams
GaInNAs Avalanche Photodiodes (APDs) Avalanche Photodiodes are highly sensitive and low noise solid-state optical detectors with internal gain –Equivalent to photo-multiplying tubes Silicon is the material of choice for <1.06 m For telecom wavelengths most III-V materials are not suitable We are investigating whether GaInNAs will be useful for application in APDs Preliminary Results –Increasing Nitrogen content increases Breakdown voltage –Reduction in tunnelling compared to InGaAsP Reverse bias voltage (V) Current (A) 1e-12 1e-11 1e-10 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 1e-3 1e-2 InGaAsP E g =0.992eV GaAs E g =1.087eV Dark Current Measurement Increase in Dark current due to tunnelling 0% Nitrogen hh Large Electric field hole Conduction band Valance band electron James Chamings, Alf Adams, Stephen Sweeney
Laser Biosensors Feasibility of an optical biosensor based on DFB laser technology that makes use of the evanescent field in the outer layers of a semiconductor waveguide Adding layers to a semiconductor waveguide changes the effective index of the guide, causing a shift in wavelength of the propagating modes. New layer ncnc nsns ngng ncnc nsns ngng Field Strength (E(y)) λ1λ1 λ2λ2 We hope to observe a change in wavelength of the DFB laser when a layer of biological molecules e.g. proteins adsorbs to the gold surface of the device. Later on we will try measuring the interference pattern between a sensing and a reference laser, and modifying the device surfaces to be analyte-specific to a wide variety of compounds. t Adsorbtion Desorbtion Δλ A major goal will be the detection of layer formation In real time. Jo Coote, Stephen Sweeney, Sub Reddy
Diamond Anvil Cell (DAC) High Pressure Physics High pressure He-gas system (up to 1.2 GPa) Laser Window gas Currently developing a Sapphire ball anvil cell for electrical and optical measurements up to 4GPa Andy Prins, Shirong Jin, Gary Strudwick, Alf Adams, Stephen Sweeney
Extended Temperature Optoelectronics (ETOE) Igor Marko, Stephen Sweeney, Alf Adams £1.7M 30 month DTI sponsored project to produce optoelectronic devices operating to high temperature Will facilitate Fibre-To-The-Home networks Large power savings ~80% due to lower cooling power (good for the environment!) New Al-containing laser materials have lower threshold currents and improved thermal stability
Applications gas sensing medical free space comms GaInAsSb Type I QWs μm Sb-based Type II ‘W’ Lasers 3 – 4.2 μm Pressure dependence of threshold current yields info on loss processes. » P » E g Temperature dependence of the spontaneous emission emitted during operation also helps analyse loss processes. Results used to further develop these devices. Mid-infrared Laser Characterisation (~2-10 μm) Kevin O’Brien, Stephen Sweeney, Alf Adams, Ben Murdin
1.3 m laser on GaAs basis to fabricate VCSELS for Metronet communications Spectroscopic results on the VCSELs: GaAsSb laser (devices and spectroscopy) Interesting material property: type I or type II © Pacific Broadband Networks - Media Release Ith strongly temperature dependent non-radiative recombination Study carrier recombination: - + Large shift of emission in both working device (spontaneous emission) as well as wafer (PL) type II Konstanze Hild, Stephen Sweeney, Igor Marko, Gunnar Blume, Jeff Hosea Using: Pressure Low temperature Life time measurements