Heterogeneous integration of InP etched facet lasers to silicon photonics by micro transfer printing

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Loi, Ruggero
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University College Cork
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Photonics Integrated Circuits allow optical functionalities and interconnects with small footprint, large band -width and -density, low heat generation. The silicon photonics platform (SOI) offers excellent waveguiding properties, large-area wafers and a highly developed CMOS infrastructure matured with electronics. Nevertheless, the key function of light amplification is missing due to the indirect band-gap of silicon. The light has to be provided to the SOI from a separate direct band-gap III-V material. InP based devices work in the infrared optical window of the electromagnetic spectrum and can be heterogeneously integrated to the SOI. This research deals with the development of the first stand-alone InP Fabry-Perot lasers heterogeneously integrated to SOI by Micro Transfer Printing (µTP). The lasers are pre-fabricated and tested before transfer and are optimized to reach excellent optical, electrical and thermal performance. Lasers printed on Si substrates emit over 20 mW optical power, have threshold current of 16 mA and series resistance of 6 Ω; the thermal impedance of 38 K/W is half of that for the same laser printed directly on the SOI. The transfer printable InP ridge lasers have been designed as rectangular coupons with both contacts at the top and etched facets at the sidewalls. Two main release technologies based on the FeCl3:H2O (1:2) solution and a InGaAs or a InAlAs sacrificial layer were developed for releasing the devices from the original InP substrate with selectivity to InP greater than 4000 at 1 ◦C. The working principle of a polymer anchor system which restrains the devices to the substrate during the undercut were determined. The devices were printed on different silicon photonic substrates with excellent adhesion, with and without adhesive layers. A process for creating recesses into the SOI was developed to allow edge coupling the laser waveguide to the SOI or a polymer waveguide. High alignment accuracy along the three spatial directions can be achieved with alignment markers, reference walls and the interposition of a metal layer beneath the devices. This work shows a possible path for the achievement of a laser source for silicon photonics and it has been the basis for the integration of others InP devices to PICs by micro transfer printing.
Laser , InP , Micro-transfer printing , Silicon photonics , Integrated photonics
Loi, R. 2019. Heterogeneous integration of InP etched facet lasers to silicon photonics by micro transfer printing. PhD Thesis, University College Cork.