Photonic crystals with glancing angle deposition

We report a study on thin silicon films fabricated with glancing angle deposition (GLAD). Morphology of these films as a function of shadowing and temperature are examined first. Columnar separation in silicon thin films is investigated with scanning electron microscopy (SEM) and Fourier transform analysis. Column spacing increases with increasing substrate tilt (shadowing). Column spacing is small and varies little with temperature in the temperature range 375–670K, then increases substantially at higher temperature. Column tilt angles of these films are close to the values predicted by Tait's rule.; Birefringent properties of bi-deposited silicon films on glass are next examined. In the bi-deposited technique, small quantities of film are deposited successively on a substrate at azimuthal positions of 0, 180; 360, …degrees. Films are analyzed by spectroscopic ellipsometry in the wavelength range 370–1670nm. These films have three distinct optical indices, and exhibit in-plane birefringence much larger than the naturally occurring birefringent materials such as calcite; or quartz. We show that the birefringence of these films is due to form anisotropy. Plan view SEM images show the presence of column bunching in the film, and subsequent Fourier analysis shows a two-fold symmetry; confirming the directional preference of column density.; Square spiral photonic crystals were fabricated with glancing angle deposition. Stop bands at multiple light incident angles indicate a partial gap close to the desired gap frequency of the photonic crystal. Optical indices of these films are determined by anisotropic ellipsometric analysis. Simulation of transmission or reflection spectra for a superlattice of 10 square spiral layers enhances and narrows the transmission drops and reflection peaks in these films at the stop band positions. A square spiral structure was deposited on a Si(100) substrate partially patterned with a square lattice of small bumps. The ellipsometric and reflection spectra for this film within the wavelength range of our instrument do not indicate the presence of a stop band. Scanning electron microscope images of the films seem to indicate that the embedded spacing has been lost. Fourier transform analysis indicates a faint four-fold symmetry in plan view SEM images of all square spiral films.