Materials and devices.for compact optical amplification in Si photonics is reviewed. In particular, as the requirement for
high gain per length together with high refractive index renders traditional oxide-based approach problematic, Er-doping
of silicon-rich silicon nitride and erbium silicate nanocrystals are proposed and shown to be promising alternatives.
Using such new materials, microdisk resonators and slot waveguides that concentrate the light in a compact volume for
high functionality are fabricated and characterized.
Micro-disk resonators were fabricated using Er doped silicon-rich silicon nitride (SRSN:Er). SRSN:Er thin films are fully CMOS-compatible and show efficient Er3+ luminescence pumped off-resonantly via Si nanoclusters. The high refractive index of SRSN (>2.0 at 1.5 μm) allows freedom in designing compact micro-disk resonators. Micro-disks with two different contents of Er (0.2 at.%, 0.02 at.%) with a diameter of 25 μm were fabricated, and characterized using evanescent coupling using tapered fibers. Whispering gallery modes with Q-factors in excess of 13000 were obtained, and FDTD calculations indicate that much higher values should be possible. Finally, we demonstrate excitation of fundamental whispering gallery mode via off-resonant, top-pumping of the SRSN microdisk.
We report on fabricating Er<sub>x</sub>Y<sub>2-x</sub>SiO<sub>5</sub> nanocrystals using ErCl<sub>3</sub>•6H<sub>2</sub>O and YCl<sub>3</sub>•6H<sub>2</sub>O solutions and Si nanowires grown
by VSL method. Use of crystalline host allows incorporation of up to 25 at % Er without clustering and loss of optical
activity, and use of Y enables continuous mixing of Er and Y for controlling cooperative upconversion. We obtain a
cooperative upconversion coefficients of (2.2±1.1)×10<sup>-18</sup> cm<sup>3</sup>/s and (5.4±2.7)×10<sup>-18</sup> cm<sup>3</sup>/s at an Er concentration of
1.2×10<sup>21</sup> cm<sup>-3</sup> and 2.0×10<sup>21</sup> cm<sup>-3</sup>, respectively. These values are up to 10 times lower at 10 times higher Er concentration
than those reported for Er-doped silica, and shows that up to 69 dB/cm gain could be achieved for ultra-compact optical
amplification. Also, we report on the deposition of Er<sub>x</sub>Y<sub>2-x</sub>SiO<sub>5</sub> thin film on Si substrate using ion beam sputter
deposition. Rapid thermal annealing at 1100°C is enough to form crystal phase the film and activate most of Er<sup>3+</sup> ions.