Compressively strained Ge channels on relaxed SiGe buffer layers

Strain-induced roughening and dislocation formation has been studied by high-resolution transmission electron microscopy (HRTEM) in compressively strained Ge quantum wells on linearly graded SiGe buffer layers grown by low-energy plasma-enhanced chemical vapour deposition (LEPECVD). We show that for appropriately chosen plasma densities and substrate temperatures, abrupt interfaces can be achieved on both sides of the Ge channels, when additional hydrogen is supplied to the reactive gases, even for channel widths above the critical thickness for dislocation formation. Optimized modulation doped Ge quantum wells (MODQWs) exhibit the highest hole mobilities observed to date, approaching values of ∼90000 cm2 V−1 s−1 for a sheet density of ∼6×1011 cm−2 at liquid He temperatures.