The Electrodynamic Gradient Freeze Growth of InP.

The advantages, in term of material quality, of III-V bulk crystal growth in a low temperature gradient environment is well recognized. The resulting low defect levels and improved material homogeneity is important for both optoelectronic devices and integrated circuit applications. In order to fully exploit this advantage the optimum temperature profile for a given set of conditions must be determined. This requires considerably more flexibility than is normally achievable with standard Bridgman or gradient freeze technology. In this report, the design of a novel, 23 zone, high pressure, vertical furnace for the electrodynamic gradient freeze (EDGF) growth of InP is described. This versatile technique allows one to electronically establish a wide range of thermal profiles. Low axial temperature gradients have been established across the advancing liquid- solid interface while the remaining melt is maintained at a temperature 30C above the melting point, thereby avoiding excessive decomposition. Undoped, seeded, 50 mm diameter InP single crystals have been grown with dislocation densities in the 10 sup 2- 10 sup 3/cm sup 2 range. The material is n-type with 77K carrier concentrations of 3x10 sup (15)/cm sup 3 and mobilities exceeding 38,000 cm sup 2 /volt cdot sec. This exceeds those normally achieved for LEC InP grown from near stoichiometric melts. The dislocation densities of the EDGF material are 50-100 times lower than comparable undoped LEC InP.