High-mobility two-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 × 105 cm2 V−1 s−1 for a density of 4.6 × 1011 cm−2 electrons. The strained layers were grown at 600 ◦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 is also discussed and both the mobility and morphology are linked to the 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 higher growth rates. For low growth rates and temperatures the 2DEG mobility as a function of sheet carrier density was found to be degraded