Experimentally verified numerical simulation of single crystal growth process with a low melt height and an axial vibration

Abstract

This Ph.D. dissertation investigates experimental and numerical crystal growth of antimony-doped germanium (Ge-Sb) single crystals. The investigation is a part of the TUBITAK project 212M030. The single crystal growth of Ge-Sb from the melt is investigated by the Vertical Bridgman (VB), Axial Heat Processing (AHP), and Axial Vibrational Control (AVC) techniques. The effects of method dependent growth parameters on the quality of the grown single crystals have been analyzed. To this end, two different pulling rates (10 mm/h and 20 mm/h), different initial melt heights (5 mm, 10 mm, 14 mm, and 58 mm), and three different sets of vibrational parameters (2 mm amplitude and 0.25 Hz frequency, 0.25 mm amplitude and 1 Hz frequency, and 0.25 mm amplitude and 25 Hz frequency) are applied in the growth of seven different crystals. It is observed that the highest single crystal length with the most homogeneous solute redistribution and the least dislocation density are achieved in an AHP crystal which is grown with the lowest pulling rate (10 mm/h). However, it is determined that an appropriate control of the vibration parameters in the AVC technique makes it possible to achieve almost the same crystal quality with doubled growth rate, so the production yield is decreased. Moreover, global and local numerical simulations are performed in order to investigate the effects of the growth parameters on the convective flow patterns. Also, results of the numerical simulations contribute to make better and more reliable interpretations of the experimental observations. The simulation results provide useful information for the experimentalists to investigate the effects of growth parameters on the temperature and solute distribution, flow pattern, and the interface shape. According to the numerical results, it is possible to clarify how the insertion of the baffle, adjusting the melt height, and optimizing the vibrational parameters of the baffle contribute the thermal and the solutal homogenization in the melt, interface stability, and consequently improved crystal quality.