Bulk growth of GaAs An overview

The III-V compound GaAs is of rising importance for opto- and microelectronics, especially, for LEDs and LDs and for high-frequency devices like HBTs, HEMTs and MMICs, respectively. The device performance and degradation mechanisms are critically influenced by bulk properties. Hence, considerable efforts are aimed at a reduction of crystal imperfections and improvement of the uniformity of physical properties connected with the need to increase the crystal diameter. This goal is not easy to attain because of the well-known proportionality between crystal diameter and dislocation density. The efforts focused on a reduction of the dislocation density (below 10(4) cm(-3) at least) by reducing the non-linearities of the thermal field in LEC growth have led to the development of fully encapsulated and vapour pressure controlled Czochralski method (FEC and VCZ, respectively). A second line to the same objective has been the improvement of the vertical Bridgman (VB) and vertical gradient freezing (VGF) methods to commercial maturity. The state of art, pros and cons, and the developments of the growth methods to be expected in future are summarized in the present paper. Some fundamental problems of heat transfer, dislocation dynamics (polygonization) and nonstoichiometry related growth phenomena are discussed more in detail. (C) 1999 Elsevier Science B.V. All rights reserved.