A novel application of the vertical gradient freeze method to the growth of high quality III–V crystals

Abstract

Large state-of-the art quality single crystals of gallium arsenide, gallium phosphide, and indium phosphide have been grown using a new process based on the vertical gradient freeze method. Seeded 50 mm diameter crystals are produced, at all levels of doping, which have lower dislocation densities than crystals grown by alternative methods. This is the first report of large diameter, low doped, ultra-low defect density InP. The radial uniformity is exceptional in these 750 gram 〈111〉 seeded InP crystals. The dislocation density of silicon-doped 〈100〉 GaAs grown by this method is less than 300/cm 2 without requiring high dopant levels. Undoped semi-insulating GaAs is stable with respect to thermal type-conversion. The results in GaP compare favorably with the reported state-of-the-art LEC crystals. The process features growth in a boron nitride seeded crucible, with axial and radial thermal gradients that are much lower than in the conventional LEC process. The establishment of an appropriate phosphorus or arsenic vapor pressure over the melt is shown to be an effective method of stoichiometry control. The process details are explained for the growth of GaP and some InP and GaAs results are presented. The equipment used in the growth apparatus, as well as the growth sequence and process control strategies, are described. The impact of the design of the hot zone elements on the shape of the liquid-solid interface is discussed. The establishment of a near planar liquid-solid interface has positive implications for radial uniformity and the occurrence of twinning and polycrystalline nucleation.