We report on a technology for the fabrication of hollow capillary optical leaky waveguides in fused silica glass. The fabrication process is based on lithography, wet chemical etching and aligned direct bonding. We have developed a single-layer photoresist soft mask which allows for channel etch depths up to 33 µm in fused silica glass. To our knowledge, such etch depths have never been achieved before in fused silica glass with single-layer soft etch masks. Aligned direct glass-glass bonding is used for the first time to obtain channels with almost circular profiles with diameters between 16 and 66 µm. Capillary optical leaky waveguides embedded into microfluidic devices can be used, for example, for capillary electrophoresis and hyper Rayleigh scattering.
In this work, the influence of ammonium sulfide (NH 4 ) 2 S passivation on waveguide based mid-infrared InAs/GaSb superlattice photodetectors (2-5 μm wavelength) has been studied. The current-voltage characteristics for reverse as well as for forward bias of passivated samples have been examined. The advantages of this have been the reduction of the reverse leakage current and the increase of zero bias resistance. As a disadvantage the decrease of the photoresponsivity after sulfur passivation has been found. Furthermore, it has been observed that the passivation solution does not only passivate the surface of GaSb, but it also reacts with entire GaSb layers and can destroy the devices.
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