MTL Annual Research Report 2012

We have demonstrated for the first time in-plane InGaAs/InP laser diodes recess-integrated with SiON waveguides on silicon substrates using a modular heterogeneous integration technique ^[1] .  This technique allows pre-testing and selection of devices before integration, it is compatible with integration on full CMOS wafers after conventional back-end processing is completed, and it can be used to integrate multiple types of devices on a single wafer.  We feel it is superior to other optoelectronic integration techniques; more broadly, it is ideally suited to realizing robust, planar, monolithically integrated micro-systems incorporating a variety of materials and devices.

In this research, 1.55-µm InGaAs/InP ridge laser diodes were fabricated in the form of platelets 150 µm wide, 300 µm long, and 6 µm thick ^[2] .  With a micropipette vacuum pick-up tool, we placed pre-selected platelet lasers into similarly sized recesses etched in a thick SiO₂ layer on a silicon wafer substrate.  The recesses intersect SiON waveguides fabricated earlier within the SiO₂ layer ^[3] and the In/Al bonding layer thicknesses were chosen so that after assembly, the waveguides of the platelet lasers will be co-axial with the SiON waveguides.  Once all the lasers are in position, the substrate is placed on a heater strip and all lasers are simultaneously bonded in place using a pressurized thermoplastic membrane to apply a uniform vertical force (20 psi) to hold them against a contact pad on the bottom of the recess while a solder bond forms. We made contact to the upper p-contact of the integrated lasers by direct probing; thin-film metal contacts deposited and patterned on the top surface could also have been used ^[1] .

The integrated laser/waveguide units operate at room temperature with lasing thresholds of 17 mA pulsed and 19 mA CW, both of which are lower than the thresholds of comparable devices on InP substrates (consistent with the higher thermal conductivity of Si) ^[4] .  Single-mode CW output powers in excess of 1 mW are measured from 1-mm-long waveguides.  Side mode suppression ratios in excess of 20 dB have been observed, and laser-to-waveguide coupling losses less than 1 dB have been measured.

The integration of pre-selected laser diodes with waveguides on Si using a simple, flexible, modular, CMOS-compatible technique is itself a significant achievement in the field of optoelectronic integration.  More generally, this approach to heterogeneous integration can be used by anyone interested in the simultaneous integration of multiple types of compound semiconductor devices with Si integrated circuits, or on other substrates.

1. J. M. Perkins and C. G. Fonstad, “ Full recess integration of small diameter low threshold VCSELs within Si-CMOS ICs,” Optics Express, vol. 16, no. 18, pp. 13955-13960, 2008. [↩] [↩]
2. J. J. Rumpler and C. G. Fonstad, IEEE Photonics Technology Letters, vol.21, no. 13, pp. 827-829, July 2009. [↩]
3. E. Barkley, PhD Thesis, Massachusetts Institute of Technology, Cambridge, 2007. [↩]
4. S. Famenini and C. G. Fonstad, “Integration of edge emitting laser diodes with dielectric waveguides on silicon,” in review. [↩]