Selective etching of
normalGaAs
in the
H2SO4‐H2O2‐H2O
system was studied as a pretreatment to selective deposition. Flat‐bottomed holes were obtained in low
H2SO4
solutions, whereas nonplanar holes were obtained in high
H2SO4
solutions. Differences between both cases are considered from the etching behaviors under nonselective conditions. Using low
H2SO4
solutions, selective etching was conducted on substrates with different crystallographic orientations. Asymmetrical holes were observed in all cases except for holes on the {001} substrate with rectangular windows held parallel to the 〈001〉 direction. The possibility of the revealed planes being the wall in the hole is discussed.
We consider further a probe fermion in a dyonic black hole background in anti-de Sitter spacetime, at zero temperature, comparing and contrasting two distinct classes of solution that have previously appeared in the literature. Each class has members labeled by an integer n, corresponding to the nth Landau level for the fermion. Our interest is in the study of the spectral function of the fermion, interpreting poles in it as indicative of quasiparticles associated with the edge of a Fermi surface in the holographically dual strongly coupled theory in a background magnetic field H at finite chemical potential. Using both analytical and numerical methods, we explicitly show how one class of solutions naturally leads to an infinite family of quasiparticle peaks, signaling the presence of a Fermi surface for each level n. We present some of the properties of these peaks, which fall into a well-behaved pattern at large n, extracting the scaling of Fermi energy with n and H, as well as the dispersion of the quasiparticles.
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