Semiconductor saturable absorber mirrors (SESAMs) are vital for enabling ultrafast fiber lasers, yet their performance is often constrained by slow carrier recovery times. This study investigates the influence of substrate miscut angle (0°, 2°, and 6° toward the [110] direction) on the properties and mode-locking performance of InGaAs/GaAsP SESAMs grown by metal-organic chemical vapor deposition (MOCVD) on (100) GaAs substrates. Comprehensive characterization via high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), photoluminescence (PL) spectroscopy , and spectrophotometry reveals that increasing the miscut angle introduces lattice defects, significantly reducing recovery time. However, larger miscut angles also increase surface roughness and nonsaturable losses, degrading nonlinear absorption. In Yb-doped fiber laser tests, SESAMs with 2°-miscut angles achieved stable mode-locking, generating 8.2 ps pulses at 1064 nm, while 6°-miscut devices exhibited deteriorated performance due to material quality degradation. This work provides critical insights into optimizing SESAMs via substrate engineering and offers practical guidelines for designing high-performance ultrafast lasers.