Bulk growth of GaAs An overview

The III-V compound GaAs is of rising importance for opto- and microelectron ics, especially, for LEDs and LDs and for high-frequency devices like HBTs, HEMTs and MMICs, respectively. The device performance and degradation mech anisms are critically influenced by bulk properties. Hence, considerable ef forts are aimed at a reduction of crystal imperfections and improvement of the uniformity of physical properties connected with the need to increase t he crystal diameter. This goal is not easy to attain because of the well-kn own proportionality between crystal diameter and dislocation density. The e fforts 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 gro wth have led to the development of fully encapsulated and vapour pressure c ontrolled Czochralski method (FEC and VCZ, respectively). A second line to the same objective has been the improvement of the vertical Bridgman (VB) a nd vertical gradient freezing (VGF) methods to commercial maturity. The sta te 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 pr oblems of heat transfer, dislocation dynamics (polygonization) and nonstoic hiometry related growth phenomena are discussed more in detail. (C) 1999 El sevier Science B.V. All rights reserved.