Fig. 1. Epitaxial stack design and the fabricated Ge/SiGe MQW microdisks. (a) Schematic of the Ge/SiGe MQW epitaxial structure. (b) Scanning electron microscope (SEM) image of a nonsuspended Ge/SiGe MQW microdisk. (c) SEM image of a suspended Ge/SiGe MQW microdisk supported by a Si post.

Fig. 2. Room-temperature PL of a suspended Ge/SiGe MQW microdisk exhibiting FP mode resonances. Inset: Bulk Ge reference showing direct bandgap emission at 1550 nm.

Fig. 3. 3D-FEM simulation for tensile-strained microdisks. (a) Schematic of type 1, type 2, and type 3 SiNx stressor configurations. (b) Cross section of the simulated strain distribution for a type 1 Ge microdisk. (c) Comparison of strain profiles for all three configurations of Ge/stressor microdisks.

Fig. 4. (a) Schematic of the epitaxial stack of the Ge/SiGe MQW microdisk. (b) Fabrication process flow for a tensile-strained, suspended Ge/SiGe MQW microdisk. (c) SEM image of a Ge/SiGe MQW microdisk without SiNx stressor [step 8 in (b)]. (d) SEM image of a Ge/SiGe MQW microdisk with SiNx stressor [step 9 in (b)].

Fig. 5. PL and Raman characterizations of Ge/SiGe MQW microdisks. (a) Room-temperature PL of strained (red and blue) and unstrained (black) microdisks. (b) Typical Raman spectrum from the center of a microdisk. (c) Raman line scan along the diameter of a strained, suspended Ge/SiGe MQW microdisk.

Fig. 6. Comparisons of simulation, PL, and Raman measurements. (a) Devices 1, 2 (440 nm thick, 6 μm diameter). (b) Devices 3, 4 (440 nm thick, 10 μm diameter). (c) Devices 5, 6 (340 nm thick, 6 μm diameter). (d) Devices 7, 8 (340 nm thick, 10 μm diameter).

Fig. 7. Optical gain calculations for Ge/SiGe MQW. (a) Band alignment of strain-balanced Ge/Si0.19Ge0.81 MQW without external strain. (b) Band alignment of strain-balanced Ge/Si0.19Ge0.81 MQW with 1% external biaxial tensile strain. (c) TE and TM net gain spectra for Ge QW with different external biaxial tensile strain, assuming n-type doping concentration of 5×1019  cm−3 and an injection of 2×1019  cm−3. Without external tensile strain, net gain is negative, meaning lasing is not achieved. As external tensile strain increases, net gain increases remarkably. Peak gain reaches positive ∼600  cm−1 with 1% of external tensile strain.

Table 1. Parameters of the Investigated Microdisks