DéFiZnO

In order to circumvent the remaining cost and technical limitations associated with the present day GaN based Light Emitting Diodes (LED) for general lighting applications, we propose to set up a research program of industrial type based on a disruptive approach and on an alternative material, ZnO. ZnO is recognised as a very promising material for the application to LED. But up to now, it has been plagued by the present inability to dope it p type in a reliable and stable way. Furthermore, ZnO based quantum well heterostructures are presently grown on lattice mismatched substrates leading to numerous defects in the active layers; These will limit the radiative efficiency of the foreseen devices and lead to difficult and spatially inhomogeneous doping. However, contrary to GaN, ZnO possesses the great advantage of being available’ although still scarcely at the industrial level - in the form of high quality and pure bulk material. The advantages that the existence of bulk ZnO materials offer are numerous; it opens the way to homoepitaxial growth for the realisation of defect free emitting structures and should greatly facilitate p type doping which is adversely affected by extended defects. Defect free ZnO quantum well heterostructures, if grown on doped substrates, will also lead to efficient near UV vertically integrated LEDs, not available with GaN heterostructures. With such near UV LEDs, phosphor conversion will result in improved colour characteristics compared to the existing technology. Homoepitaxially grown quantum well structures, if grown homoepitaxially on non polar ZnO surfaces, will also alleviate the problem associated to internal electric fields that otherwise limit the radiative efficiency in the QW active area of the LEDs. Along these lines, and in order to fully exploit the still potential advantages associated to homoepitaxial growth of ZnO structures, the proposed project focuses on the following points: - the development of a crystal growth method for large dimension structurally perfect and stoechiometric ZnO crystals on an industrially compatible set-up, in order to address the problem of limited availability of ZnO bulk substrates in terms of size, purity, non polar orientations, and doped materials - obtaining ‘epiready’ ZnO wafers in polar and non-polar orientations in order to cope with problems of surface contamination and to eliminate sub-surface damage layer that up to now have limited the structural perfection of homoepitaxial layers - the development of homoepitaxial low temperature processes on these plar and non polar substrates that will yield epilayers without mismatch induced defects and with improved p-type dopability, opening the way to efficient, vertically integrated UV LEDs based on ZnO. The project consortium will comprise two government laboratories with a strong expertise respectively in the field of bulk ZnO growth and in epitaxial growth, together with three private SMEs, the first being a world actor in crystal growth manufacturing, the second of them being a world leading producer of epitaxial growth machines and the third one being specialised in wafer conditioning. This Project deals with the first and compulsory step towards the realisation of a new disruptive, low cost, high yield technology for the second generation of high performance LEDs based on ZnO for general lighting applications. .