  Side and top silicon nitride stressors were proposed and shown to be
effective ways to reduce the threshold current Ith and improve the wall-plug
efficiency {\eta}wp of Ge-on-Si lasers. Side stressors only turned out to be a
more efficient way to increase {\eta}wp than using top and side stressors
together. With the side stressors only and geometry optimizations, a {\eta}wp
of 30.5% and an Ith of 50 mA (Jth of 37 kA/cm2) can be achieved with the defect
limited carrier lifetime of 1 nsec. With the defect limited carrier lifetime of
10 nsec, an Ith of 7.8 mA (Jth of 5.8 kA/cm2) and a wall-plug efficiency of
38.7% can be achieved. These are tremendous improvements from the case without
any stressors. These results give strong support to the Ge-on-Si laser
technology and provide an effective way to improve the Ge laser performance.
