SiGe-based FETs: buffer issues and device results

SiGe quantum well structures gain increasing interest in the Si technology. The preparation of a Si channel or a Ge-rich or even a pure cc channel wit h a respective two-dimensional carrier gas opens the attractive possibility to fabricate high performance n- or p-type field effect transistors. For b oth device types, a virtual substrate surface is required which is created by a strain relieved buffer layer grown on a Si standard wafer. The paper r eviews various approaches of SiGe buffers including special attempts to red uce the thickness and to improve the quality. N- and p-type modulation-dope d field-effect transistors are presented which show comparably good device characteristics and cut-off frequencies in the range of 100-120 GHz. (C) 20 00 Elsevier Science B.V. All rights reserved.