Growth of 4‑Inch InP Single-Crystal Wafer Using the VGF-VB Technique

High-quality Indium phosphide (InP) single crystals are mainly grown using Vertical Gradient Freeze (VGF) or Vertical Bridgman (VB) methods. However, producing large-diameter (>4-in.) single crystals with uniform and controlled doping concentrations poses significant challenges. This study proposes a combination of VGF and VB techniques (VGF-VB) as a feasible solution to this problem. The process involves placing a pyrolytic boron nitride (PBN) crucible filled with seed crystals, InP polycrystals, boron oxide, and dopant into a vacuum-sealed quartz tube. This sealed quartz tube is loaded into a nominally 4.5-in. VGF-VB InP single-crystal furnace for a 4-in. wafer. The polycrystalline InP is melted and bonded to the seed crystal during the growth process using the VGF method. Once the crystal growth reaches the shoulder growth stage, the VB method is adopted to form the cylindrical section of the crystal. Using this VGF+VB technique, the resulting nominally 4.5-in. InP single crystals exhibit a maximum etch pit density (EPD) of ≤ 300 cm^-2 at the tail end and an electrical parameter uniformity improved to within ± 6%. Structural and spectral analyses of EPD, Hall effect, and photoluminescence (PL) confirm that the VGF-VB crystal growth technique is reliable for producing high-quality InP single crystals.