Research Toward a Heterogeneously Integrated InGaN Laser on Silicon

This is the authors' abstract. We don't add key points for this paper.

A heterogeneously integrated InGaN laser diode (LD) on Si is proposed as a path toward visible wavelength photonic integrated circuits (PICs) on Si. Herein, InGaN films are vertically stacked on a TiO 2 waveguide (WG) fabricated on a Si wafer by bonding. In the light propagation direction, it is composed of a hybrid InGaN/TiO 2 section, a TiO 2 WG, an adiabatic taper, and mirrors that can form a cavity. As the refractive index of GaN is well matched with that of TiO 2 , the optical transverse mode extends to both the GaN and TiO 2 in a hybrid mode. Modes between a hybrid InGaN/TiO 2 and a pure TiO 2 WG can transfer with an adiabatic taper structure. The coupling loss is calculated to be less than 0.5 dB with fairly short taper length of 78 μm and tip width of 200 nm. GaN substrate removal and bonding are critical fabrication steps of this LD and PIC. The substrate removal is successfully done by photoelectrochemical etching. Although direct bonding of GaN wafers with thermal oxide on Si is successful, GaN epitaxial wafers are more difficult. An implication and remedy of this is discussed in terms of surface roughness of GaN epitaxial film.