Wantage, United Kingdom
Wantage, United Kingdom

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Khokhar A.Z.,University of Glasgow | Parsons K.,MacDermid Autotype Ltd | Hubbard G.,MacDermid Autotype Ltd | Rahman F.,University of Glasgow | And 13 more authors.
Microelectronic Engineering | Year: 2010

We describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity. © 2010 Elsevier Ltd. All rights reserved.


Grant
Agency: Cordis | Branch: FP7 | Program: CP-IP | Phase: NMP-2008-2.2-1 | Award Amount: 11.95M | Year: 2009

Solid state light sources based on compound semiconductors are opening a new era in general lighting and will contribute significantly to a sustainable energy saving. For a successful and broad penetration of LEDs into the general lighting market two key factors are required: high efficiency and low cost. Two new disruptive technologies based on nanostructured semiconductors are proposed to address these key factors. A novel epitaxial growth technique based on nanorod coalescence will be explored to realize ultra-low defect density templates which will enable strain-relieved growth of LEDs and thus achieve higher efficiency. The second highly innovative approach is the growth of directly emitting Gallium nitride based nanorod structures. These structures are expected to produce exceptionally high efficiency devices covering the whole visible spectrum and even phosphor-free white LEDs. Significantly, our new nanostructured compound semiconductor based technology will enable LED growth on low-cost and large-area substrates (e.g., Silicon) as wafer bowing will be eliminated and thus lead to a dramatic reduction in production costs. The main objectives over the three years are: Profound understanding of the growth mechanisms and properties of nanorod systems New materials and process technologies (wafer-scale nanoimprinting, dry etching, device processing) for LEDs based on nanostructured templates and nanorod-LEDs Demonstrators: -Phosphor-converted white LEDs based on nanostructured sapphire templates (efficacy 150 lm/W @ 350 mA) and Silicon templates (efficacy 100 lm/W @ 350 mA) -Blue, green, yellow and red emitting Nano-LEDs (external quantum efficiency 10%) -Novel phosphor-free white-emitting Nano-LEDs (external quantum efficiency 2%) Realising the objectives of SMASH will start a new generation of affordable, energy-efficient solid state light sources for the general lighting market and will push the LED lamp and luminaire business in Europe.


Nasir M.E.,University of Bath | Allsopp D.W.E.,University of Bath | Bowen C.R.,University of Bath | Hubbard G.,MacDermid Autotype Ltd | Parsons K.P.,MacDermid Autotype Ltd
Nanotechnology | Year: 2010

This paper describes the formation of mono-domain highly ordered nanoporous alumina on the scale of a 2inch diameter silicon wafer by anodization of aluminium evaporated on a patterned SiO2 mask on a silicon substrate. The position of the ordered pores correlates with holes in the SiO2 mask, which guide the electric field during anodization and initiates pore nucleation. The technique is suitable for the production of ordered nanoporous alumina on a wafer scale and overcomes the time, cost and scale limitations of existing processes. © 2010 IOP Publishing Ltd.


Hubbard G.,MacDermid Autotype Ltd | Hubbard G.,University of Bath | Nasir M.E.,University of Bath | Shields P.,University of Bath | And 5 more authors.
Nanotechnology | Year: 2012

Anodic porous alumina nanostructures have been fabricated with tapered and cylindrical pores with a spacing of 100 and 200nm and depth of 180500nm. The porous nanostructures were replicated into polymer films to create a moth-eye anti-reflecting surface by a roll-to-roll UV replication process. The angle dependent optical transmission of the resulting polymer films exhibited up to a 2% increase in transmission at a normal angle and up to a 5% increase in transmission at a 70°angle of incidence to an equivalent film with a surface replicated from polished aluminum. No significant difference was observed between the optical performance of moth-eye surfaces formed from cylindrical and tapered nano-pores. © 2012 IOP Publishing Ltd.


Kapur N.,University of Leeds | Abbott S.J.,MacDermid Autotype Ltd | Dolden E.D.,Sharp Corporation | Gaskell P.H.,University of Leeds
IEEE Transactions on Components, Packaging and Manufacturing Technology | Year: 2013

A novel mathematical model is presented of the liquid transfer process encountered during screen printing, enabling the prediction of the volume of liquid removed from a mesh and printed on a substrate with reasonable accuracy. It is based on the key assumption that free surface effects dominate and the printed liquid is pulled out of, rather than flows from, the mesh. The model is validated against an extensive range of benchmark data from both on- and off-screen printing trials. The agreement is found to be remarkably good. In addition, the model is able to offer considerable insight to practitioners and liquid manufacturers alike - a key result being that the screen printing process can be made essentially independent of many of the set-up parameters in the operating range adopted by most practitioners. © 2011-2012 IEEE.


Khokhar A.Z.,University of Glasgow | Parsons K.,MacDermid Autotype Ltd. | Hubbard G.,MacDermid Autotype Ltd. | Watson I.M.,University of Strathclyde | And 12 more authors.
Applied Optics | Year: 2011

Experimentally measured optical properties of photonic crystal LEDs are reported here. Photonic crystal and photonic quasi-crystal structures were fabricated on GaN epilayer LED wafer material using both direct-write electron beam lithography and nanoimprint lithography. Some of these structures were processed to make finished LEDs. Both electroluminescence and photoluminescence measurements were performed on these structures. Devices were characterized for their current-voltage characteristics, emission spectra, far-field emission pattern, and angular emission pattern. These results are useful for fabricating photonic crystal LEDs and assessing their operational properties. © 2011 Optical Society of America.


Tillin M.,Sharp Corporation | Charlton M.D.B.,University of Southampton | Gong Z.,University of Strathclyde | Khokhar A.Z.,University of Glasgow | And 10 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal (PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative contributions to performance improvements from effective index reduction effects that alter the conditions for total internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically improved extraction performance. Comparisons are made with the performance of recently fabricated devices. © 2010 Copyright SPIE - The International Society for Optical Engineering.

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