Holographic realization of hexagonal two dimensional photonic crystal structures with elliptical geometry
Schematic diagram of process procedures for realizing hexagonal 2D photonic crystals by means of two-beam interference principle with double-exposure steps.
(a) Light intensity distribution under double-exposure of two-beam interference. (b) Inhibitor concentration in the exposed photoresist during the photosensitization process. (c) Dissolution rate of the exposed photoresist in a developer. (d) Resultant patterns after development. Two-dimensional periodic patterns with a hexagonal lattice of elliptical pillars can be realized.
Evolution of the calculated profiles with the normalized exposure energy (the numbers in the figure) for positive photoresist films double exposed to an interference pattern. By carefully controlling the total exposure doses, two-dimensional periodic holes or pillars can be realized by using a positive photoresist. Development time in this figure is set to 8 s (N: nonexposed region, S: single-exposed region, and D: double-exposed region).
Calculated profiles under different exposure energies. (Hollow-square and solid-circle symbols show the diameters of holes and pillars, respectively, while hollow-circle and solid-diamond symbols show the ellipticity of holes and pillars, respectively.)
Photonic bandgap maps of the calculated profiles under different exposure energy. (Solid-diamond and hollow-cross symbols show the TM- and TE-mode gaps, respectively.)
Schematic diagram of our laser holography system
(a) Reflectivity variation under different thickness of AR coating layer with an incident wavelength of 325 nm. The structure of the test sample is shown in the inset of the figure. (Solid and dot curves are simulation results while square symbols are experimental data. (b) 200 nm thick PhC templates using an 80 nm thick AR coating layer. Sidewall distortion on the resultant patterns caused from back-reflection can be clearly seen.
(Color online) (a) SEM pictures of fabricated two-dimensional hexagonal pillars. 370 nm thick PhC templates with a high aspect ratio and vertical sidewalls are realized using a 160 nm thick AR coating layer. (b) Photographs of the resultant samples under tilted angles of illumination. Bright and uniform diffracted light throughout the sample proves a good quality of the resultant patterns. The samples are highly uniform in an area of and present good reproducibility.
Experimental profiles under different exposure energy. Eight uniformly hexagonal photonic crystal samples are fabricated with a lattice constant of 420 nm. SEM pictures of the corresponding structures are shown around the analytical plot which shows the diameter and ellipticity of the resultant pattern with the exposure energy. (Hollow-square and solid-circle symbols show the diameters of holes and pillars, respectively, while hollow-circle and solid-diamond symbols show the ellipticity of holes and pillars, respectively.)
Experimental profiles under different development time. Four 200 nm thick hexagonal photonic crystal samples are fabricated with a lattice constant of 420 nm. SEM pictures of the corresponding structures are shown above the analytical plot which shows the diameter and ellipticity of the resultant pattern with the development time. (Solid-circle symbol shows the diameter of pillars while solid-diamond symbol shows the ellipticity of the pillars.)
Sequence of the experimental steps for transferring PhC patterns into silicon substrate by means of lift-off process and etching technique.
SEM pictures of the resultant patterns after (a) Cr evaporation (procedure 2 of Fig. 11), (b) lift-off using a blue-tape (procedure 3 of Fig. 11), and (c) dry etching into silicon (procedure 6 of Fig. 11)
Cross-sectional and tilted SEM views of vertical silicon nanopillars with an aspect ratio of 10 using a single-step deep reactive ion etching and controlled mixture of gases.
Parameters for simulation of profiles of holographic photonic crystals.
Article metrics loading...
Full text loading...