Low Threshold Electrically-Pumped Hybrid Silicon Microring Lasers

We report on significantly improved performance of a compact hybrid silicon microring lasers obtained by selectively reducing the volume of active region. This is done by appropriately undercutting the multiple quantum well (MQW) region to force carriers to flow toward the outer edge of the microring for better gain/optical mode overlap. We observe a reduction of the threshold of over 20% and up to 80% output power enhancement. These are primarily due to the improved injection efficiency. We developed a diode laser model that includes nonradiative recombination. The model and the experimental results highlight the benefits, as well as the negative effects from excessive undercutting, including lower MQW confinement, higher modal loss, and higher thermal impedance. A design rule for MQW undercutting is, therefore, provided.