Design, modeling, and characterization of high-performance 1550-nm InGaAsP/InP spot-size converter integrated waveguide photodiode

We present the multiscale simulation, theoretical modeling, fabrication, and experimental characterization of a compact, high-performance InGaAsP/InP spot-size-converter integrated waveguide photodiode (SSC-WGPD) operating at λ  = 1550 nm. This novel SSC-WGPD architecture, featuring a single-quantum-well (QW) photoabsorber asymmetrically embedded within a thick i-superlattice region, enables end-on butt-coupled integration of a fiber-matched passive waveguide, high-speed WGPD, and adiabatic mode transformer. These three functional sections, their integration, and the common epitaxial structure are jointly optimized using a calibrated 8-band k  ·  p Schrödinger–Poisson solver, TCAD, and optical simulations. The optimized architecture is then realized using ZrO ₂ -based selective-area impurity-free QW intermixing. Experimental demonstration of a 3 × 50~ µ m ² device shows a ∼four-fold improvement in responsivity, reaching ∼0.64 A/W, together with low dark current (∼1 nA), high internal quantum efficiency (>90 %), and an estimated RC-limited bandwidth of 60 GHz at a low bias of −2 V, highlighting its potential for next-generation photodetection applications.