PIC-integrable, uniformly tensile-strained Ge-on-insulator photodiodes enabled by recessed SiN x stressor

Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride (SiNx) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56% tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750 MPa tensile stress. The device exhibits a responsivity of 1.84±0.15  A/W at 1550 nm. The extracted Ge absorption coefficient is enhanced by ∼3.2× to 8340  cm−1 at 1612 nm and is superior to that of In0.53Ga0.47As up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coefficient improvement of 10%–20% in the C-band and 40%–60% in the L-band was observed. This work facilitates the recess-strained GOI photodiodes for free-space PIC applications and paves the way for various (e.g., Ge, GeSn or III-V based) uniformly strained photonic devices on PICs.