We have developed an ion beam assisted deposition (IBAD) texturing process for biaxially aligned films as substrates for GaN epitaxy. The IBAD process enables low-cost, large-area flexible metal foil substrates to be used as potential alternatives to single-crystal sapphire and silicon for GaN electronic devices. Epitaxial GaN films are grown by the MOCVD process on these engineered flexible substrates. We have achieved epi GaN films of several microns on polycrystalline metal foils that have in-plane and out-of-plane alignment of less than 1° FWHM and typical threading dislocation densities of 4-8 x 10^8/cm^2.
We use the epitaxial GaN films on IBAD/polycrystalline metal foil as a template to deposit epitaxial multi-quantum well light emitting diode (LED) InGaN structures. From these layered structures we have successfully fabricated LED devices. These are the first LED devices fabricated directly on metal foil. We observe photoluminescence intensities from the LED structures up to 70% of those fabricated on sapphire. We will present data on performance of such devices and how these LED devices could be printed using a roll-to-roll process.
This work was supported by the Department of Energy ARPA-E agency.
In this study we introduce Gallium Nitride (GaN) nanowire (NW) as high aspect ratio tip with excellent durability for nano-scale metrology. GaN NWs have superior mechanical property and young modulus compare to commercial Si and Carbon tips which results in having less bending issue during measurement. The GaN NWs are prepared via two different methods: i) Catalyst-free selected area growth, using Metal Organic Chemical Vapor Deposition (MOCVD), ii) top-down approach by employing Au nanoparticles as the mask material in dry-etch process. To achieve small diameter tips, the semipolar planes of the NWs grown by MOCVD are etched using AZ400k. The diameter of the NWs fabricated using the top down process is controlled by using different size of nanoparticles and by Inductively Coupled Plasma etching. NWs with various diameters were manipulated on Si cantilevers using Focus Ion Beam (FIB) to make tips for AFM measurement. A Si (110) substrate containing nano-scale grooves with vertical 900 walls were used as a sample for inspection. AFM measurements were carried out in tapping modes for both types of nanowires (top-down and bottom-up grown nanowires) and results are compared with conventional Si and carbon nanotube tips. It is shown our fabricated tips are robust and have improved edge resolution over conventional Si tips. GaN tips made with NW’s fabricated using our top down method are also shown to retain the gold nanoparticle at tip, which showed enhanced field effects in Raman spectroscopy.
The growth of ordered arrays of group III-nitride nanostructures on c-plane gallium nitride (GaN) on sapphire using selective-area metal organic chemical vapor deposition (MOCVD) is presented. The growth of these nanostructures promotes strain relaxation that allows the combination of high indium content active regions with very low dislocation densities and also gives access to nonpolar and semipolar crystallographic orientations of GaN. The influence of the starting template and the growth conditions on the growth rate and morphology is discussed. The growth of indium gallium nitride (InGaN) active region shells on these nanostructures is discussed and the stability of various crystallographic orientations under typical growth conditions is studied. Finally, the effect of the growth conditions on the morphology of pyramidal stripe LEDs is discussed and preliminary results on electrical injection of these LEDs are presented.
Nanostructures such as carbon nanotubes, nanowires and graphene nanoribbons are being intensively explored for future
nanoelectronic and nanophotonic applications. In order for these nanosystems to progress from the research laboratory to
technology, it is critical to precisely understand and control charge injection at the contacts and subsequent charge
transport. In this paper, we discuss recent experimental and theoretical results on electrical contacts to Ge nanowires and
electronic transport in GaN and InAs nanowires. It is shown that both the properties of the nanocontacts and the charge
transport differ significantly from those of bulk systems.