Growth of 20 mm diameter GaAs crystals by the floating-zone technique with controlled As-vapour pressure under microgravity

Abstract

Five GaAs single crystals with diameters of 20 mm were grown by the floating-zone technique (FZ) under microgravity during the second German Spacelab Mission D-2. Both Si-doped and undoped semi-insulating GaAs feed material was used for studying a variety of crystal growth phenomena and material properties of relevance for GaAs melt growth. The GaAs rods were sealed in silica ampoules which contained an integrated As source to provide controlled stoichiometry conditions. The heating system consisted of a specially designed mirror furnace (PARELLI). In this paper we present results of the microgravity experiments concerning technical aspects, such as the control of interface curvature and crystal diameter, as well as studies of the density and distribution of dislocations. The formation of dopant striations is used as an indicator for the state of the Marangoni convection in the GaAs melt zone and the influence of a magnetic field. Results of photoluminescence studies show an improvement with respect to the dislocation network formation by a strong increase of the cell size. Both oxygen and boron contents of the space-grown crystals are very low. Results of numerical calculations of the curvature of the interface, the distribution of temperature and stress in the crystal are shown to be in good agreement with the experiments.