Lifetime-limiting mechanisms of integrated IR sources for silicon photonics

Abstract

The fully epitaxial integration of IR laser sources into modern photonic circuits built on Si or SOI wafers is severely limited by the thermal-and lattice-constant mismatch between the substrate and the III-V layers that are required to achieve efficient solid-state lasing in the near infrared range. To overcome these limitations, modern commerciallyavailable SiPh technologies employ selective wafer/device bonding techniques that allow to separately grow the III-V emitter and to integrate it into the photonic integrated circuit (PIC) at a later processing stage. Conversely, state-ofthe-art devices leverage InAs quantum-dot (QD)-based active regions to highly reduce the sensitivity of the laser diode to the presence of the extended defects, which are generated as a consequence of the heteroepitaxial growth. In term of reliability, high levels of maturity have been demonstrated by both types of sources, either on the field or at laboratory level. Despite this, several degradation mechanisms still affect the long-term operation of such devices, thus limiting their useful lifetime. The aim of this paper is to discuss on the dominant degradation processes related to integrated laser sources for silicon photonics. This goal is achieved by summarizing some of the most recent results that have been obtained on two different, but well representative, classes of solid-state lasers: heterogeneously integrated quantum well (QW)-based emitters, such as vertical-cavity silicon-integrated lasers (VCSILs) emitting at 945 nm and III-V 1.55 m lasers bonded on silicon-on-insulator (SOI) substrates, and InAs QD laser diodes (LDs) epitaxially-grown on silicon, emitting in the 1.31 m window.