We demonstrate a post-growth in-situ chlorine passivation for suppressing surface-dominant transport in Si nanowires
(SiNWs). The leakage current of bridged SiNWs suppressed more than five orders of magnitude as a result of chlorine
passivation while the shape and structural properties of the bridging NWs remain unaffected by the post-growth in-situ
HCl passivation. The chlorine passivated SiNW surfaces were found to be beneficial to enhance the high immunity to
environmental degradation.
KEYWORDS: Silicon, Gold, Field effect transistors, Chemical vapor deposition, Transmission electron microscopy, Thin films, Oxides, Annealing, Scanning electron microscopy, Nanowires
For high speed and performance field effect transistor with high carrier mobility, vertically aligned Si <110> nanowires
is demonstrated by chemical vapor deposition via a vapor-liquid-solid growth mechanism. We found that the
orientation of NWs was changed from <111> direction to <110> direction on a Si (110) substrate with increasing the
growth temperature above ~ 610°C by changing Au-Si eutectic phase. These vertically aligned <110> oriented SiNWs
with significantly high carrier mobility opens up new opportunities for high speed and performance future electronic
device applications.
We report a simple sonochemical method for the seeding and synthesis of Zinc Oxide nanowire arrays that can be
formed on a number of substrates that are stable in alcohol and aqueous solution. Vertically aligned ZnO NWs were
synthesized from a single solution at room-ambient via ultrasonic excitation. Prior to the NW growth, a ZnO seed
layer was deposited using the same system with a different solution. The optimal conditions to produce a high
density of oriented wires along with their optical characteristics are presented for ZnO NWs with a significantly high
growth rate compared with traditional growth techniques such as evaporation, chemical vapor deposition and
sputtering. Our method promises a mass-manufacturable process for fast and inexpensive ZnO NW production for
practical low cost electronics, photonics and energy conversion applications.
The growth of crystalline 1D nanowires of semiconductors on non-epitaxial surfaces holds the promise to overcome
many of the current challenges of heteroepitaxial material synthesis and device fabrication for a wide range of electronic
and photonic applications. Nano-heteroepitaxial bridging of CVD grown nanowires potentially enables a low cost and
mass-manufacturable approach to nanowire based device fabrication. Here we report the synthesis and bridging of lateral
silicon nanowires between a pair of vertical non-single crystal surfaces and application of this technique in the design
and fabrication of waveguide-integrated photodetectors. The device consists of a number of 1D nanowires laterally
grown across gaps etched into rib optical waveguides with an amorphous silicon oxynitride core and silicon oxide
claddings. A pair of phosphorous-doped polysilicon electrodes was deposited on the walls of the waveguide gap for
electrical interfacing of the nanowires to collect the photocurrent under optical excitation. Characterization results
demonstrated good waveguide characteristics, high electrical isolation between the electrodes, low leakage current and
distinct photoresponse from the bridged nanowires. This implementation of silicon nanowires on polysilicon combines
the characteristics of crystalline 1D nanowires with the flexible fabrication processes on non-single-crystal silicon
platforms facilitating advances in silicon photonics and beyond.
We report a novel method to fabricating single crystal and highly oriented 1-D Silicon micropillars and nanowires and
then transferring them to coat a target surface of any topology using an innovative harvest/lift-off process. This method
enables highly crystalline micro- and nano- pillars of different materials with diverse bandgaps and physical properties
to be fabricated on appropriate mother substrates and transferred to form multilayered 3D stacks for multifunctional
devices. This approach not only ensures the incorporation of any kind of material (with the best device characteristics)
on a single substrate facilitating substrate-free device fabrications on any topology, but also allows the repeated use of a
mother substrate for continual production of new devices. This capability of fabricating substrate-less devices will offer
a universal platform for material integration and allow solar active devices to be coated on various surface topologies
that would be suitable for solar hydrogen generation.
PdZn was used to improve the electrical properties of p-GaN annealed at low activation temperature for high efficiency
green light-emitting diodes (LEDs). A hole concentration of p-GaN annealed at 600 °C with PdZn was almost 28 times
higher than that of p-GaN annealed at 800 °C without PdZn. SIMS analysis showed that hydrogen concentration in p-GaN annealed with PdZn is decreased compared to that without using PdZn because the PdZn enhances hydrogen
desorption from the Mg-doped p-GaN film at low temperature. The green MQW LED annealed at 600 °C using PdZn
showed improved electrical characteristic and optical output power compared to that annealed at 800 °C without using
PdZn. These results are attributed to the increase of hole concentration of p-GaN due to removal of hydrogen in p-GaN by PdZn and the decrease in thermal damage of MQW at low activation temperature.
We demonstrate phosphor-free light-emitting diode (LED) by growing InGaN/GaN multiple quantum wells (MQWs) on
the n-GaN microfacets. The white emission was realized by combining emissions from InGaN/GaN MQWs grown on cplane
(0001), semipolar {11-22} and {1-101} facets which are selectively grown on n-GaN with trapezoidal shape
arrays. The photoluminescence (PL) and electroluminescence (EL) measurement revealed that the long wavelength light
was emitted from InGaN/GaN MQWs grown on c-plane (0001), while the short wavelength light was emitted from that
of semipolar microfacets. The change in the emission wavelengths from each microfacets was due to the difference in
the well thickness and In composition of each MQWs. The LED showed white emission at an injection current between
180 and 230 mA. These results suggested that white emission is possible without using the phosphor by combining
emission lights emitted from microfacets.
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