Heterogeneous integration of photonics

Heterogeneous integration of different materials and modules on integrated photonics is necessary to implement a functional optical system. For Si photonics, as an example, it lacks of light sources and high efficient photodetectors in the near infrared spectrum. To accomplish active functions, we need to integrate other material systems on the Si photonics platform. However, to effectively integrate other material on host photonics with high quality is technically challenging. In our lab, we study several novel materials and develop techniques to integrate them on Si photonics.

Rapid Melt Growth Method

A unique process called rapid melt growth (RMG) method, in combination with the self-aligned microbonding technique, is applied to heterogeneously integrate monocrystalline semiconductor on Si photonic devices. This process doesn’t require complex epitaxy process steps to deal with the lattice mismatch issue between different semiconductors, and the thermal budget is relatively small, which is most compatible with the standard CMOS process. We use this approach to develop various heterogeneous device structures.

Self-Aligned Butt-Coupled Ge/Si Waveguide Photodetector

The Ge on Si infrared waveguide photodetectors had been investigated by many groups. To increase the photoresponsivity, the Ge absorber should be butt-coupled to the Si waveguide to get efficient light absorption. However, no suitable approach by far is presented to epitaxially grow single crystal Ge on Si on the same planar structure. A new process using self-aligned microbonding technique to make Ge/Si butt-coupled MSM waveguide photodetectors is demonstrated. With this technique, the photodetector exhibits low dark current and high responsivity.

GaSb MSM Photodetectors on Si Waveguides

Metal–semiconductor–metal (MSM) photodetectors made of gallium antimonide (GaSb) on silicon waveguides by the rapid melt growth method are investigated. By controlling the thermodynamics of crystal regrowth and optimizing the process condition, single-crystal GaSb stripes are monolithically integrated on the silicon substrate. The MSM GaSb waveguide photodetector shows a responsivity of 0.57 A/W at 1550 nm.

SU-8 Optical Mode Converters for Coupling Between Fibers and Silicon Photonic Wires With Large Misalignment Tolerance

A wideband optical mode converter is presented for coupling between fibers and sub-wavelength silicon photonic wires with large misalignment tolerance. This converter consists of a three-dimensional (3-D) SU-8 taper and silicon inverted nanotapers, which are cascaded and show coupling losses of 2.8 dB and 4.1 dB for the TE- and TM-polarized waves launched from a cleaved single mode fiber. The fiber misalignment tolerance for 3-dB transmittance drop is estimated to be 3um.

Colorful Silicon-nanocrystal resonant-cavity light emitting devices

A silicon-nanocrsytal resonant-cavity light-emitting device (RCLED) is presented. The microcavity, made by a silicon nanocrystal layer inserted between a semitransparent Au reflector and a distributed Bragg reflector mirror, shows enhanced emission intensity by four times at resonance wavelength and 1/8 narrow emission spectrum compared to nonresonant devices. The external quantum efficiency and power conversion efficiency also increase by 3.5 times. Multiple colors, green, green-yellow, orange, and red are displayed by adjusting the cavity length of RCLED