Heterogeneously integrated Vernier laser with 10-nm BCB bonding and their thermal analysis

Abstract

We report heterogeneously integrated Si/III-V two-ring Vernier lasers featuring a 10-nm divinylsiloxane-bis-benzocyclobutene (BCB) bonding layer, which is the thinnest to our knowledge. The fabricated laser device demonstrates a double-facet output power of 13.6 mW, a linewidth of 2.6 kHz, a free spectral range (FSR) of 40 nm, and a side mode suppression ratio (SMSR) of 46 dB. These values are comparable to those of a directly bonded Vernier laser structure, which is thermally ideal. The comparability is attributed to a small thermal impedance value of 45.1 K/W, which was experimentally measured with a new method developed for lasers with extensive passive sections. A laser model calibrated with experimental inputs predicts that the output power of a 10-nm BCB bonded Vernier laser with a 4-µm current aperture differs from that of a directly bonded one by less than 10% even beyond a thermal rollover. It is also anticipated that the 10-nm BCB bonded laser can emit a few mW even at an ambient temperature of 120 °C. Such a high-temperature operation capability is desirable for light detection and ranging (LiDAR) chip applications. The investigated 10-nm BCB bonding approach can be an attractive alternative for cases where a relaxed surface roughness condition is beneficial.