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Sn-doped InP is being used as a platform for a wide variety of fiber communications components, including lasers, LEDs, semiconductor optical amplifiers, modulators and photo-detectors. The more the diameter is, the more imperfection of the InP crystal would be. The substrates with large diameter are desired in order to realize low devices cost. In recent years, we have developed a high quality 3-inch and 4-inch Sn-doped InP single crystal growth using the HP-LEC method after P-injection direct synthesis polycrystalline. It is found that by carefully adjusting the thermal symmetry of the heating field and by further improving the quality of the polycrystalline, three inch and four inch twin-free Sn-doped InP crystals can be obtained even with a shoulder angle of up to 35°-90°, and defects caused by thermal decomposition appear on the surface of the crystals during pulling. For <111> LEC InP crystals, twin formation can be effectively suppressed by optimization of growth conditions, such as thermal field, doping concentration, etc. However, it is difficult to grow twin-free <100> LEC InP in a similar way. It is observed that the yield of single crystal <100> InP can be increased by controlling the ingot shape of a gradually increased diameter.