Toward controlling the Al2O3/ZnO interface properties by in situ ALD preparation.

An Al2O3/ZnO heterojunction was grown on a Si single crystal substrate by subsequent thermal and plasma-assisted atomic layer deposition (ALD) in situ. The band offsets of the heterointerface were then studied by consecutive removal of the layers by argon sputtering, followed by in situ X-ray photoelectron spectroscopy. The valence band maximum and conduction band minimum of Al2O3 are found to be 1.1 eV below and 2.3 eV above those of ZnO, resulting in a type-I staggered heterojunction. An apparent reduction of ZnO to elemental Zn in the interface region was detected in the Zn 2p core level and Zn L3MM Auger spectra. This suggests an interface formation different from previous models. The reduction of ZnO to Zn in the interface region accompanied by the creation of oxygen vacancies in ZnO results in an upward band bending at the interface. Therefore, this study suggests that interfacial properties such as the band bending as well as the valence and conduction band offsets should be in situ controllable to a certain extent by careful selection of the process parameters.

Vertical optical ring resonators fully integrated with nanophotonic waveguides on silicon-on-insulator substrates.

We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step toward 3D photonic integration. The on-chip integration is realized by rolling up 2D differentially strained TiO(2) nanomembranes into 3D microtube cavities on a nanophotonic microchip. The integration configuration allows for out-of-plane optical coupling between the in-plane nanowaveguides and the vertical microtube cavities as a compact and mechanically stable optical unit, which could enable refined vertical light transfer in 3D stacks of multiple photonic layers. In this vertical transmission scheme, resonant filtering of optical signals at telecommunication wavelengths is demonstrated based on subwavelength thick-walled microcavities. Moreover, an array of microtube cavities is prepared, and each microtube cavity is integrated with multiple waveguides, which opens up interesting perspectives toward parallel and multi-routing through a single-cavity device as well as high-throughput optofluidic sensing schemes.

Matching p-i-n-junctions and optical modes enables fast and ultra-small silicon modulators.

In this article a new method is presented that allows for low loss implementation of fast carrier transport structures in diffraction limited photonic crystal resonators. We utilize a 'node-matched doping' process in which precise silicon doping results in comb-like shaped, highly-doped diode areas that are matched to the spatial field distribution of the optical modes of a Fabry-Pérot resonator. While the doping is only applied to areas with low optical field strength, the intrinsic diode region overlaps with an optical field maximum. The presented node-matched diode-modulators, combining small size, high-speed, thermal stability and energy-efficient switching could become the centerpiece for monolithically integrated transceivers.

Continuously tunable delay line based on SOI tapered Bragg gratings.

The realization of an integrated delay line using tapered Bragg gratings in a drop-filter configuration is presented. The device is fabricated on silicon-on-insulator (SOI) rib waveguides using a Deep-UV 248 nm lithography. The continuous delay tunability is achieved using the thermo-optical effect, showing experimentally that a tuning range of 450 ps can be obtained with a tuning coefficient of -51 ps/°C. Furthermore the system performance is considered, showing that an operation at a bit rate of 25 Gbit/s can be achieved, and could be extended to 80 Gbit/s with the addition of a proper dispersion compensation.