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 (${\mathrm{SiN}}_x$) 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 $1.84\pm 0.15\mathrm{A}/\mathrm{W}$ at 1550 nm. The extracted Ge absorption coefficient is enhanced by $～3.2\times$ to $8340{\mathrm{cm}}^{-1}$ at 1612 nm and is superior to that of ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coefficient improvement of 10%–20% in the $\mathrm{C}$-band and 40%–60% in the $\mathrm{L}$-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.