Germanium-On-Insulator based photonics is a promising technological platform. As part of the initial development of a germanium photonic platform, optical losses in passive structures and electrical injection for active components have been studied on Germanium-On-Insulator (GeOI) substrates fabricated using Smart-Cut™ technology . The low threading dislocation density of the germanium (Ge) film is expected to reduce unwanted carrier recombination leading to improved performance of the passive and active Ge components.
Fiber-couplers and 500nm square waveguides have been fabricated from 200-mm GeOI substrates allowing optical loss measurements in the TM mode at a wavelength of 2.3µm. Propagation losses were evaluated at 1.5dB/cm. Circular-shaped radius bends and evanescent couplers/splitters have also been simulated, fabricated and characterized to determine the bending losses and the coupling coefficient for ring resonators. Furthermore, innovative bend shapes showed lower bending losses than those with circular-shaped radii, which would allow higher component densities.
Finally, the electrical injection is of prime importance in fabricating efficient active components on GeOI. For this, the rectifying or ohmic behavior at the metal-semiconductor contact and its dependence as a function of the Ge doping or metal type has to be precisely known. In particular, we examined the challenging question of the contact resistance between metal and n-type Ge. A study has been conducted using Transfer Length Model (TLM) structures to determine the most suitable metal to contact n-doped and p-doped germanium.
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 Kang, J. et al. Opt. Express 24, 11855-11864 (2016).