Heterogeneously Integrated Membrane Lasers on Si Substrate for Low Operating Energy Optical Links

High demand exists for low-operating energy optical links that use wavelength division multiplexing (WDM) technologies in datacenter networks. Thus, we fabricate a directly-modulated membrane distributed-reflector (DR) laser with low operating energy on a thermally-oxidized silicon (Si) substrate. Because we use epitaxial growth to bury an active region on a directly-bonded InP-based membrane, it needs to be kept within a critical thickness, which is related to the growth temperature and the thermal expansion coefficients of materials. In previous studies, we used 250-nm-thick structures, causing relatively large series resistance that limited device performance on such aspects as energy cost, output power, etc. In this study, we increase the III-V membrane thickness to 350 nm, which is close to the calculated critical thicknesses. We achieve the same high crystal quality of multi-quantum-wells (MQWs) found in our previous studies. The fabricated laser shows a differential resistance of 72 $\Omega$ and thermal resistance of 982 K/W. Thanks to a reduction in bias voltage, the laser can be directly modulated at 25.8 Gbit/s with an energy cost of 97 fJ/bit. In addition, due to a reduction in heat generation, direct modulation with a 50-Gbit/s NRZ signal is demonstrated by increasing bias current up to 10 mA.