Achieving
a high output power and a high energy efficiency in ultraviolet light-emitting
devices requires a reduction in the dislocation density of an underlying GaN
template. Conventional thin film growth is a two-step process that starts with
a low-temperature buffer layer (also known as the wetting or nucleation layer),
followed by the growth of high-temperature GaN islands that eventually coalesce
and planarize to form the basic template for device structures. We have studied
these initial growth stages and showed that reducing the density of GaN islands
contributes to the reduction in dislocation density. However, an excessive
reduction in island density leads to the worsening of film surface morphology,
with the appearance of pits and spiral features. We have observed that
dislocation density is related to the crystal tilts of GaN nucleation islands
and that pits and spirals are generated from the screw-type dislocation bundles
formed at low GaN island densities. The alternative use of AlN templates
(instead of conventional GaN buffer layers) consequently improves the c-axis crystal orientation
and reduces the threading dislocation density in the GaN films while
simultaneously providing a high-quality surface morphology.
Source:IOPscience
For more information, please visit our website:
send us email at sales@powerwaywafer.com and powerwaymaterial@gmail.com
No comments:
Post a Comment