Interfacial and electrical properties of atomic-layer-deposited
HfO2
gate dielectric on epitaxial GaAs (epi-GaAs)/Ge and bulk GaAs substrates have been investigated. Atomic layer deposition provides a unique opportunity to integrate high quality gate dielectrics on epi-GaAs. The cross-sectional transmission electron microscopy of a
HfO2
/III-V gate stack shows a similar interfacial layer thickness for
HfO2
on bulk p-GaAs and epi-GaAs substrates. However, X-ray photoelectron spectroscopy shows a Ga oxide-rich interfacial layer after postdeposition annealing at
500°C
for films grown on epi-GaAs. Although the epi-GaAs surface is rough with nanoscale features, the electrical properties of the
HfO2
gate dielectric deposited on epi-GaAs are comparable with bulk p-GaAs-based devices. The Au/
HfO2
/epi-GaAs gate stack shows a low frequency dispersion (13%), hysteresis voltage (0.72 V), and a leakage current density of
2.1×10−3Acm−2
at
VFB+1V
(where FB is flatband) for an equivalent oxide thickness of 1.4 nm.
We report on the process parameters of nanoimprint lithography for the fabrication of two-dimensional (2D) photonic crystals. The nickel mold with 2D photonic crystal patterns covering an area up to 20 mm2 is produced by electron-beam lithography and electroplating. Periodic pillars as high as 200 nm to 250 nm are produced on the mold with the diameters ranging from 180 nm to 500 nm. Optimization of process parameters is essential to generate high-quality nanoscale patterns and control the residual stress in the mold. The mold is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mold are well transferred. This process can be utilized for commercial applications of photonic crystal devices.
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