HIGH-MOBILITY 2-DIMENSIONAL ELECTRON GASES IN SI SIGE HETEROSTRUCTURES ON RELAXED SIGE LAYERS GROWN AT HIGH-TEMPERATURE/

Low-temperature mobilities for two-dimensional electron gases (2DEGs) formed in tensile-strained Si/SiGe heterostructures are reported, with values up to 2.7 x 10(5) cm(2) V-1 s(-1) for a density of 4.6 x 10(11 ) cm(-2) electrons. The strained layers were grown at 600 degrees C in a ultra-high-vacuum chemical vapour deposition system using SiH4 and GeH4 operating at around 20 Pa, The surface morphology of the layers i s also discussed and both the mobility and morphology are linked to th e quality of the virtual substrates. The virtual substrate consists of strain-relaxed SiGe alloys grown on Si(001) substrates; we show that it is preferable to grow these substrates at higher temperatures and h igher growth rates. For low growth rates and temperatures the 2DEG mob ility as a function of sheet carrier density was found to be degraded.