Origin of mechanical strain and its spatial uniformity enhancement from recessed silicon nitride sidewall stressor

Wavelength bandwidth is a key performance metric for emerging optical interconnects targeting high-data-rate communications. Strain engineering has proven effective in tailoring the wavelength bandwidth of Ge photonic devices. Although a recessed SiN sidewall stressor was found to extend the absorption edge of Ge photodetectors (PDs) into the L-band with a responsivity improvement of >3×, the working mechanism of the recessed stressor remains poorly understood. Here, we attribute the strain enhancement and its spatial uniformity improvement in Ge PDs to the removal of the compressive strain at the bottom edge corners of the Ge strip. PDs employing the stressors exhibit electrical responses consistent with the mechanism. These findings offer a general framework for applying recessed SiN sidewall stressors to semiconductor photonic devices.