(Invited) Heterogeneously Integrated III-V on Silicon Lasers

Silicon photonics has generated an outstanding interest for optical telecommunications and inter/intra-chip interconnects in microelectronic systems. This platform can address a wide range of applications from very short distance data communication to long haul optical transmission.

Recent research has focused on the realization of silicon optoelectronic integrated devices using large scale, low-cost, and highly accurate CMOS technology. While silicon is now considered as the material of choice for passive optical components due to its low-loss beyond 1.1 µm and high-index-contrast with its native oxide, it is however a very poor light-emitting material. Today, practical Si-based light sources are still missing, despite the demonstration of an electrically pumped germanium laser.

Silicon-based compounds are commonly used in commercial optical waveguide devices for applications such as passive optical interconnects and biomedical sensors. However, the integration of lasers together with Si integrated photonics-electronic circuits has proved to be much more challenging. The complexity lies in the fact that silicon is a poor light-emitting material due to its indirect energy bandgap. In addition, the direct growth of standard III-V materials on Si substrates is still a major obstacle because of the mismatch in lattice constants and in thermal expansion coefficients. Although light emission from silicon is not straightforward, the development of an efficient electrically pumped laser is essential to make silicon the material of choice for monolithic optoelectronic integration.

A different way consists in coupling laser beams emerging from III-V heterostructures to silicon waveguides. This so-called hybrid integration can be done using different techniques like flip-chip bonding [1] or self-assembly [2]. Both approaches present the disadvantage of requiring submicron precision alignment to enable efficient coupling between lasers and silicon waveguides. Even if the cost of a silicon photonic circuit is generally low, aligning precisely a laser chip to a planar photonic circuit is quite expensive, time consuming and unsuitable for high-volume fabrication.

A particularly promising approach instead is based on molecular bonding of III-V materials on top of a patterned Si-on-Insulator (SOI) substrate. This can be performed at the die or wafer level, depending on the application needs. Then, hybrid Si/III-V lasers are realized following a collective fabrication procedure, enabling complex photonic integrated systems onto the silicon platform [3]. Using this technology, Fabry–Pérot, racetrack, distributed feedback and Bragg reflectors lasers were demonstrated [4-5].

In this communication, we describe the hybrid platform and we present the recent advances on III-V/Si lasers and transmitters.

References

1. K. Kato et al., IEEE J. Sel. Tops. Quantum Electron, 6, 4-13 (2000).
2. J. Sasaki et al., IEEE Transactions on Advanced Packaging, 24, 569-575 (2001).
3. J.M. Fedeli et al., Advances in Optical Technologies, 2008, 412518 (2008).
4. B. Ben Bakir et al., Opt. Exp., vol. 19, no. 11, pp. 10317–10325 (2011).
5. A. Descos et al. Eur. Conf. Opt. Commun., Th.1.B.2, pp. 687-689, London, U.K. (2013).