Effect of Different Dopants on Dislocation Defects in VGF-InP and Inhibition Mechanisms

In this study, we integrate first-principles calculations with experimental statistics to systematically elucidate the fundamentally distinct mechanisms of S and Fe doping on dislocation defects in vertical gradient freeze (VGF)-grown indium phosphide (InP) crystals. Atomic-scale analysis reveals, for the first time, that S substitution at P sites forms shorter and stronger In-S bonds (bond length shortened from 2.54 to 2.42 Å), inducing significant lattice hardening (elastic modulus increased by ∼15%). The resultant local strain field effectively pins dislocations, significantly lowering the dislocation density. Experiments confirm the dislocation density hierarchy: heavily S-doped < lightly S-doped < nondoped. Conversely, Fe doping reduces the material's yield strength and stacking fault energy. Furthermore, due to its extremely low solid solubility, Fe leads to supersaturation and precipitation of FeP₂ secondary phases during VGF. Crystal quality characterization (X-ray diffraction (XRD) and Raman) indicates that high S-doped samples exhibit superior crystalline integrity, while Fe-doped samples (especially the tail) show the poorest quality. Based on these mechanisms, we optimized the VGF + VB process to control the solid-liquid interface and solute segregation, effectively suppressing Fe precipitation and improving dislocation distribution and electrical uniformity. This research provides a crucial theoretical foundation and a clear process pathway for the rational design of InP single crystals with both excellent electrical properties and ultrahigh structural integrity.