Improvement of photoluminescence from Ge layer with patterned Si3N4 stressors

Lattice strain applied by patterned Si3N4 stressors in order to improve the optical properties of Ge layers directly grown on a Si substrate was investigated. Patterned Si3N4 stressors were fabricated by various methods and their effects on the strain and photoluminescence were studied. Although we found that when the stressor was fabricated by thermal chemical vapor deposition (CVD), the Ge waveguide was tensilely and compressively strained in the edge and center positions, respectively, and photoluminescence (PL) could be improved by decreasing the width of the waveguide, the crystallinity of the Ge waveguide was degraded by the thermal impact of the deposition process. Low-temperature methods were therefore used to make the patterned stressors. The tensile strain of the Ge layer increased from 0.14% to 0.2% when the stressor was grown by plasma enhanced CVD at 350 °C, but the effects of the increased tensile strain could not be confirmed because the Si3N4 layer was unstable when irradiated with the excitation light used in photoluminescence measurements. Si3N4 stressors grown by inductively coupled plasma CVD at room temperature increased the tensile strain of the Ge layer up to 0.4%, thus red-shifting the PL peak and obviously increasing the PL intensity. These results indicate that the Si3N4 stressors fabricated by the room-temperature process efficiently improve the performance of Ge light-emitting devices.