p-type Ge channel modulation doped heterostructures with very high room-temperature mobilities

p-type Si/Si0.3Ge0.7/Ge/Si0.3Ge0.7 modulation-doped (MOD) heterostructures with very high room-temperature mobility (View the MathML source) have been successfully obtained by improving low-temperature (LT) buffer layers as pseudo SiGe substrates. The Ge channel MOD structures were fabricated on top of two kinds of LT buffer layers (Si0.3Ge0.7), which both had very thin layers (0.5–1 μm) and excellent properties such as low threading dislocation density (TDD) View the MathML source), small surface roughness (1–3 nm), and almost total relaxation (>95%), which were far superior to those of compositionally graded buffer layers (TDD: View the MathML source, surface roughness: >10 nm). The effect of the Ge/SiGe interface roughness in both kinds of LT buffer layers on the mobility was studied.