New virtual substrate concept for vertical MOS transistors

We propose a new concept of thin SiGe virtual substrates in which the inter actions of point defects with dislocations play a key role. Being purposely introduced in the thin SiGe buffer layers during their metastable growth, point defects promote the relaxation of strain. Firstly, they cause disloca tions to climb which helps to annihilate threading dislocation arms with op posite Burgers vectors. Secondly, condensation of point defects results in prismatic dislocation loops inside the layers which avoids nucleation from the surface sites. As a consequence, point defects reduce the density of ex isting threading dislocations and prevent the generation of new ones. This solution should allow the formation of virtual substrates with thin relaxed SiGe buffer layers and low threading dislocation density. In this paper, w e explain how point defects can be injected using modified MBE process tech niques. These techniques utilize either the injection of low energy Si+ ion s or super saturation of point defects resulting from very low temperature growth. (C) 1998 Elsevier Science S.A. All rights reserved.