65,548 research outputs found
Growth of single-crystal gallium nitride
Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces
Effect of Buffer Layer and III/V Ratio on the Surface Morphology of GaN Grown by MBE
The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and "loop" defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS
Ultrafast Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop
GaN is a key material for lighting technology. Yet, the carrier transport and
ultrafast dynamics that are central in GaN light emitting devices are not
completely understood. We present first-principles calculations of carrier
dynamics in GaN, focusing on electron-phonon (e-ph) scattering and the cooling
and nanoscale dynamics of hot carriers. We find that e-ph scattering is
significantly faster for holes compared to electrons, and that for hot carriers
with an initial 0.51 eV excess energy, holes take a significantly shorter
time (0.1 ps) to relax to the band edge compared to electrons, which take
1 ps. The asymmetry in the hot carrier dynamics is shown to originate
from the valence band degeneracy, the heavier effective mass of holes compared
to electrons, and the details of the coupling to different phonon modes in the
valence and conduction bands. We show that the slow cooling of hot electrons
and their long ballistic mean free paths (over 3 nm) are a possible cause of
efficiency droop in GaN light emitting diodes. Taken together, our work sheds
light on the ultrafast dynamics of hot carriers in GaN and the nanoscale origin
of efficiency droop.Comment: Submitted, 10 pages, 4 figure
First Personal Nineties R&B Soul EP
For this project, the artist Gan Xu made the first personal EP with 5 tracks including four full-length tracks and an outro. The purpose of this EP was to express the artist’s emotion and stories throughout this year in Spain, with its main theme of love, pain and growth. The genres focused on R&B, Soul, and Ballad. This EP would also be a brand new chapter and meaningful journey for the artist Gan Xu transforming from a physicist to a musician.https://remix.berklee.edu/graduate-studies-production-technology/1198/thumbnail.jp
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