Utilizing nanosphere lithography by convective self-assembly method for fabrication of periodic patterned sapphire substrate
Date Issued
2008
Date
2008
Author(s)
Liu, Shin-Yu
Abstract
As electronic devices become smaller, the traditional photolithography technology is not available to fabricate nanometer-scale structure. Nevertheless, a new technology called nanolithography is growing up nowadays. Nanostructures fabricated by nanomasks, such as naorods, nanowires, etc. are applied in optoelectronics widely. The nanosphere lithography (NSL) is one of the techniques in nanolithography which can fabricate two-dimensional and three-dimensional photonic crystal in order to manipulate the light propagating in the way we desire or fabricating periodic metal arrays which induce localized surface plasmon resonance (LSPR). It can also be used in bio-sensor and to enhance Raman spectroscopy. For our purpose, we utilize the nanospheres as the nanomasks to fabricate patterned sapphire substrate (PSS), which can be further grown by gallium nitride (GaN) laterally as a lateral epitaxial patterned sapphire (LEPS). Less threading dislocation density of nitride-based light-emitting diode (LED) is found using lateral epitaxy technique, dislocation density in active region decides the carrier lifetime, mobility and the most important characteristic in LED --- the radiative recombination rate. As the dislocation density decreases, the radiative recombination rates increases which leads to higher internal quantum efficiency. Nevertheless, the enhanced light output of LED is not only due to the increment of internal quantum efficiency but also the light extraction efficiency, lights scattered at the interface between PSS and nitride epilayers may escape into air instead of absorbed by underneath metal contact.
Subjects
Nanosphere lithography
Patterned sapphire substrate
Wet etching
Type
thesis
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