Strained silicon FETs on thin SiGe virtual substrates produced by He implantation: reduced self-heating on DC and RF performance

Abstract

In this work, MODFET layer stacks with a Ge fraction x=33% were grown by molecular beam epitaxy on thin virtual substrate (VS). A method has been developed to produce thin SRB (strain relieved buffer) SiGe layers (100-200 nm) using He implantation and subsequent annealing (750-900 /spl deg/C) to relax the strain of a pseudomorphic SiGe layer. The degree of relaxation was measured by high resolution X-ray diffraction. To assess the impact of self-heating, the output characteristics were recorded with an ACCENT Diva D225 system in the static and in the pulsed mode with 200 ns pulses at a duty cycle of 1:1000. The difference in the I/V curve between the static and the pulsed mode is much larger for the thick VS indicating enhanced self-heating. Finally, RF measurements up to 50 GHz were carried out on the two VS versions.