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Figure 4: (Left) The BIANCHO team have fabricated the world’s first electrically pumped bismuth containing laser – an GaBi0.022
As/AlGaAs
single quantum well laser diode. (Right) Light-current relationship for a 50 µm x 1000 µm GaBiAs/AlGaAs single quantum well laser at room temperature. The lasing spectrum is shown in the inset
carefully designing these growth conditions, we have been able to form high-quality GaBiAs single-quantum-well lasers with a bismuth incorporation of 2.2 percent. These devices, measured in ‘as-cleaved’ form under pulsed operation to minimize heating effects, produce 950 nm emission at room temperature and have a threshold current density of 1560 A cm-2 (see Figure 4).Our next goal is to systematically increase the bismuth composition in the active region of these lasers, with the aim of achieving 1550 nm lasing while the spin-orbit splitting energy exceeds the bandgap.
The BIANCHO team The BIANCHO team, led by Tyndall, is pursuing suppression of Auger
recombination with the alloy GaBiAs. This approach was originally presented and patented in 2010 by academic Stephen Sweeney from the University of
Surrey.Five institutions are involved in BIANCHO:
£ Researchers at Philipps University Marburg, Germany, (Kerstin Volz, Peter Ludewig and Nikolai Knaub) are performing MOCVD growth and structural characterisation of bismuth-based alloys.
£ Scientists at FTMC Lithuania, (Arunas Krotkus, Renata Butkute, and Vaidas Pacebutas), are pursuing MBE growth and characterization of bismide epitaxial layers.
£ Researchers at the University of Surrey (Stephen Sweeney, Igor Marko, Shirong Jin, Konstanze Hild and Zahida Batool) have pioneered the concept of bismuth-based alloys for device
applications, and combined device modeling with state-of-the-art experimental techniques to determine electronic and optical properties of semiconductor materials and devices.
£ Theorists at Tyndall National Institute, Ireland, (Eoin O’Reilly, Muhammad Usman (who led the preparation of this article) and Christopher Broderick) are developing theoretical models to simulate and predict the optolectronic propoerties of dilute bismide alloys and devices.
£ Engineers at CIP Technologies UK are leading the fabrication work, developing processes for this new material class.
56
www.compoundsemiconductor.net August / September 2013
Commercialisation of our technology is being driven by CIP Technologies of Martlesham Heath, UK. This company, which is now a part of Huawei, has been developing designs and fabrication processes for making lasers and modulators with these new materials.
Future targets Funding for our project continues to July 2014, and over the coming months we will spend our time focusing on increasing the bismuth content in single- and multi-quantum-well GaBix
As1-x lasers,
until the spin-orbit splitting energy in these devices exceeds the bandgap energy. This should unlock the door to an Auger-free 1550 nm laser. This is our highest priority, because it will enable devices with greatly reduced cooling (and hence energy) requirements and consequently a simpler circuit design. Our epitaxy experts are trying to grow heterostructures by MOCVD and MBE that feature bismide-based wells with a bismuth content in excess of 10 percent, and our team is also pursuing the practical realization of temperature- insensitive, electro-absorption modulators based on the quaternary alloy GaBix
Ny on a GaAs substrate.
In addition, we are investigating the growth and characteristics of other bismides. This includes the alloy GaBiNAs, which offers significant scope for tailoring the optical and electronic properties of new devices. Nitrogen and bismuth have opposite effects on material strain, making it possible to grow lattice-matched GaBiNAs layers that combine narrow band gaps with almost independently controllable band offsets and an enhanced spin- orbit splitting. In other words, GaBiNAs has the potential to produce high-efficiency, mid-infrared emitters on GaAs substrates.
One class of device that falls into this category is the mid-infrared VCSEL. This could combine reflective mirrors built from GaAs and AlGaAs, a pair of materials with a significant difference in refractive indices, with an efficient mid-infrared
As1-x-y and grown
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