Journal of the Japanese Association for Crystal Growth

An artificial crystal structure has been fabricated exhibiting a full three-dimensional photonic bandgap effect at mid-infrared to optical communication wavelengths. The photonic crystal was constructed by stacking micrometer to sub-micrometer period semiconductor stripes with the accuracy of 30 nm by advanced wafer-fusion technique. The bandgap effect of larger than 40 dB (corresponds to 99.99% reflection) was successfully achieved. The result encourages us to create an ultra-small optical integrated circuit including a three-dimensional photonic crystal waveguide with sharp bend.

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Autocloning is a reliable fabrication method for photonic crystals, which is based on stacking multilayers by sputter deposition and shaping by sputter etching. For we increase the freedom of the shaping process for unit cells ofthe autocloned photonic crystals, we have developed a new fabrication process by introducing reactive ion etching into autocloning. Utilizing the new process, we can fabricate a non layer-by-layer structure unlike usual autocloned structures. The new process leads to the development of new structures and new possibilities of autocloning. In this paper, we report the details of the process, the new structures, and its applications.

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Optical properties of two-dimensional (2D) material, with a spatially periodic index of refraction, have recently attracted growing interest because of the potential for the fabrication of novel optoelectronic deyices. We describe here the fabrication of 2D photonic band-gap structures for the visible or near infrared wavelength region using ideally ordered anodic porous alumina. An ideally ordered anodic porous alumina, which consists of an ordered triangular array of air cylinders with high aspect ratios in alumina matrix, is formed using anodization of the pretextured Al. The transmission properties of the obtained structure showed a stop band in the spectrum which corresponds to the band gap in the 2D photonic crystals. Photonic bandgap structures based on the anodic porous alumina are useful for application in several fields which require 2D photonic crystals with high aspect ratios, such as the measurement of the excited lifetime of molecules, tunable filters and highly efficient lasers.

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The semi-insulating (SI) behaviors on InP have been examined by the phosphorus vapor pressure controlled wafer annealing method. Undoped InP crystals are of n type conductivity and seem to have native defects which may be related to phosphorus vacancies. Carrier concentrations of undoped InP were decreased in the range of 10^<13> to 10^<14> cm^<-3> after wafer annealing at 950℃ under the atmospheric phosphorus vapor pressure, but SI property was not obtained since there are no any native deep levels for pinning the Fermi-level . Extremely low Fe doped InP with the Fe concentration of 1.5×10^<15> cm^<-3> was converted from conductive to semi-insulating by annealing at higher than 940℃ under the phosphorus vapor pressure of 0.1 MPa. The compensation mechanism of annealed SI InP can be explained as slight amount of Fe is electrically activated by high temperature annealing and the carrier concentration of shallow donors which may be native defects such as phosphorus vacancies is decreased to the level of less than the concentration of activated Fe. Furthermore, it was found that the two-step wafer annealing is very effective to improve the uniformity of electrical electrical properties of annealed SI InP wafers.

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