Nanofabrication and Characterization of Photonic Crystals

Citation

Cheng, Chuan-cheng (1998) Nanofabrication and Characterization of Photonic Crystals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/sjy2-r565. https://resolver.caltech.edu/CaltechETD:etd-01182008-132046

Abstract

Both techniques and applications of nanofabrication have been explored in the field of periodic dielectric nanostructures. These periodic dielectric structures are expected to exhibit interesting properties in both fields of physics and engineering. These artificial nanostructures are named "photonic crystals" because photons demonstrate similar behavior in these structures as electrons in natural semiconductor crystals. In order to construct these crystals in the optical regime, suitable nanofabrication techniques have to be developed and demonstrated, including high resolution electron beam lithography and anisotropic chemically assisted ion beam etching. In this work, both 2D and 3D photonic crystals are fabricated and characterized in the near-infrared range.

In the first part of this thesis, exploration of resolution limit of nanofabrication will be demonstrated and discussed. 15nm structures with 30nm period dot arrays and 20nm line width with 40mn period gratings are presented. Along with high resolution lithography, anisotropic pattern transfer is also developed. These powerful fabrication techniques enable us to miniaturize the dimension of both electronic and optical devices into the nanometer regime.

In the second and third part of this thesis, detailed experiments and characterization of 2D and 3D photonic crystals are discussed. A brief introduction and a theoretical simulation are also presented. In the second part, computer generated form-birefringent nanostructures are first discussed and their performance demonstrated to agree well with design using rigorous coupled wave analysis (RCWA). In-plane 2D photonic crystals used as beam splitting micropolarizers are introduced and fabricated. High extinction ratios (>820:1) between transmitted TE and TM modes are measured. These in-plane photonic crystals are the first working devices using the idea of 2D photonic crystals. Three-dimensional artificial photonic crystals with a complete 3D bandgap represent a more attractive idea.

In the third part of this thesis, we challenge the nanofabrication limits encountered when fabricating a 3D photonic crystal. The first three-dimensional photonic crystals with a forbidden photonic bandgap lying in the near infrared region of the electromagnetic spectrum, 1.1 μm < λ < 1.5 μ, just beyond the electronic band-edge of Gallium Arsenide (GaAs) are demonstrated in the world. These 3D photonic crystals were originally proposed by E. Yablonovitch and can now be fabricated using anisotropic angle etching at three directions through a hexagonal hole array mask. The field distribution using filtered finite-difference time-domain (FFDTD) calculation is briefly discussed. Development of the fabrication techniques and the optical transmission characterization are shown. Photonic crystals with up to six repeating layers are obtained and presented 90% attenuation of transmission measurement in the bandgap region. We also show the spectral shift in the transmission measurement corresponding with 2D lithographic control of microfabrication. Those artificial photonic crystals are expected to be useful in the study of inhibition of spontaneous emission and single-mode light-emitting diodes.

Thesis Files