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.