| Abstract |
In recent years, two-dimensional materials, exhibiting unique properties in comparison
with their bulk counterparts, have become a new field of interest. Group III-nitride
semiconductors have also attracted the interest of researchers in the last two decades
for their widespread applications in electronics and optoelectronics. Recently, there have
been some efforts in the literature towards the fabrication of two-dimensional GaN, which
would be an advantageous system in terms of its large band-gap and increased quantum
confinement. However, these efforts have encountered difficulties related to their limited
thickness and lateral size control.
In this work, we explore a new method for the fabrication of free-standing GaN
membranes with varying thickness of 30, 10 and 5nm, by applying the photo-electrochemical
(PEC) etching technique on especially-prepared GaN heterostructrures grown by molecular
beam epitaxy. The idea is based on the selective etching of a sacrificial InGaN layer
leading to free-standing GaN membranes, placed on the top of the structures. In most
of our PEC experiments, we observed enhanced vertical etching of the top GaN layer, in
contrast to the much preferred lateral etching direction, we originally envisaged. This was
mainly due to the deficient In-composition of the sacrificial layer, obliging us to excite
much closer to the GaN gap, thus inducing vertical etching of the top GaN surface. We
successfully transferred this vertically-etched nanostructured GaN on PDMS, but we did
not succeed in transferring it further from PDMS onto SiO2=Si templates, for optical and
SEM observations. In addition, in the samples with 5 and 10nm thick top GaN layers,
we observed vertical etching phenomena without any photo-excitation, leading us to the
conclusion that the ultrathin top GaN layers should be protected during PEC etching
procedure.
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Towards two-dimensional Gallium Nitride
