Reduced Pressure - Chemical Vapor Deposition of high Ge content (20% - 55%) SiGe virtual substrates

Abstract

We have studied the strain state, film and surface morphology of SiGe virtual substrates (Ge concentrations in-between 20% and 55%) grown by reduced pressure–chemical vapor deposition. The macroscopic degree of strain relaxation of those virtual substrates is equal to 97.2 ± 1.5%. The misfit dislocations generated to relax the lattice mismatch between Si and SiGe are mostly confined inside the graded layer. Indeed, the threading dislocations density obtained for Ge concentrations of 20% and 26% is indeed typically of the order of 7.5 ± 2.5 10⁵cm^–2. Low surface root mean square roughness have been obtained, with values in-between 2 and 5 nm. In order to check the electronic quality of our layers, we have grown a MODFET-like heterostructure, with a buried tensile-strained Si channel 8 nm thick embedded inside SiGe 26%. We have obtained a well-behaved 2-dimensional electron gas in the Si channel, with electron sheet densities and mobilities at 1.45K of 5.4×10¹¹ cm⁻² and 212 000 cm² V⁻¹ s⁻¹, respectively.