This paper introduces the principle method and simulation of an asymmetric TE （transverse electric） mode absorption in a lossy artificial metamaterial （LHM （left-handed material））. LHM is sandwiched between a lo...This paper introduces the principle method and simulation of an asymmetric TE （transverse electric） mode absorption in a lossy artificial metamaterial （LHM （left-handed material））. LHM is sandwiched between a lossy substrate and covered by a lossless dielectric cladding. The asymmetry solutions of the eigenvalue equation describe lossy-guided modes with complex-valued propagation constants. The dispersion relations, normalized field and the longitudinal attenuation were numerically solved for a given set of parameters： frequency range; film＇s thicknesses; and TE mode order. We found that high order modes, which are guided in thinner films, generally have more loss of power than low-order modes since the mode attenuation along z-axis Ofz increases to negative values as the mode＇s number increases, and the film thickness decreases. Moreover, for LHM, at incident wavelength = 1.9 /an, refractive index = -3.74＋i2 and at thickness = 0.3μm, the modes of order （4, 5, 6） attain high positive attenuation which means these modes have larger absorption lengths and they are better absorber than the others. This LHM is appropriate for solar cell applications. For arbitrary LHM, at frequency band of wavelengt （600, 700 to 900 nm）, the best absorption is attained at longer wavelengths and for lower order modes at wider films. The obtained results could be useful for the design of future light absorbers.展开更多
The integration of gallium nitride(GaN)nanowire light-emitting diodes(nanoLEDs)on flexible substrates offers opportunities for applications beyond rigid solid-state lighting(e.g.,for wearable optoelectronics and benda...The integration of gallium nitride(GaN)nanowire light-emitting diodes(nanoLEDs)on flexible substrates offers opportunities for applications beyond rigid solid-state lighting(e.g.,for wearable optoelectronics and bendable inorganic displays).Here,we report on a fast physical transfer route based on femtosecond laser lift-off(fs-LLO)to realize wafer-scale top–down GaN nanoLED arrays on unconventional platforms.Combined with photolithography and hybrid etching processes,we successfully transferred GaN blue nanoLEDs from a full two-inch sapphire substrate onto a flexible copper(Cu)foil with a high nanowire density(~107 wires/cm2),transfer yield(~99.5%),and reproducibility.Various nanoanalytical measurements were conducted to evaluate the performance and limitations of the fs-LLO technique as well as to gain insights into physical material properties such as strain relaxation and assess the maturity of the transfer process.This work could enable the easy recycling of native growth substrates and inspire the development of large-scale hybrid GaN nanowire optoelectronic devices by solely employing standard epitaxial LED wafers(i.e.,customized LED wafers with additional embedded sacrificial materials and a complicated growth process are not required).展开更多
文摘This paper introduces the principle method and simulation of an asymmetric TE （transverse electric） mode absorption in a lossy artificial metamaterial （LHM （left-handed material））. LHM is sandwiched between a lossy substrate and covered by a lossless dielectric cladding. The asymmetry solutions of the eigenvalue equation describe lossy-guided modes with complex-valued propagation constants. The dispersion relations, normalized field and the longitudinal attenuation were numerically solved for a given set of parameters： frequency range; film＇s thicknesses; and TE mode order. We found that high order modes, which are guided in thinner films, generally have more loss of power than low-order modes since the mode attenuation along z-axis Ofz increases to negative values as the mode＇s number increases, and the film thickness decreases. Moreover, for LHM, at incident wavelength = 1.9 /an, refractive index = -3.74＋i2 and at thickness = 0.3μm, the modes of order （4, 5, 6） attain high positive attenuation which means these modes have larger absorption lengths and they are better absorber than the others. This LHM is appropriate for solar cell applications. For arbitrary LHM, at frequency band of wavelengt （600, 700 to 900 nm）, the best absorption is attained at longer wavelengths and for lower order modes at wider films. The obtained results could be useful for the design of future light absorbers.
文摘The integration of gallium nitride(GaN)nanowire light-emitting diodes(nanoLEDs)on flexible substrates offers opportunities for applications beyond rigid solid-state lighting(e.g.,for wearable optoelectronics and bendable inorganic displays).Here,we report on a fast physical transfer route based on femtosecond laser lift-off(fs-LLO)to realize wafer-scale top–down GaN nanoLED arrays on unconventional platforms.Combined with photolithography and hybrid etching processes,we successfully transferred GaN blue nanoLEDs from a full two-inch sapphire substrate onto a flexible copper(Cu)foil with a high nanowire density(~107 wires/cm2),transfer yield(~99.5%),and reproducibility.Various nanoanalytical measurements were conducted to evaluate the performance and limitations of the fs-LLO technique as well as to gain insights into physical material properties such as strain relaxation and assess the maturity of the transfer process.This work could enable the easy recycling of native growth substrates and inspire the development of large-scale hybrid GaN nanowire optoelectronic devices by solely employing standard epitaxial LED wafers(i.e.,customized LED wafers with additional embedded sacrificial materials and a complicated growth process are not required).
