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

Abstract

p-type Si/Si0.3Ge0.7/Ge/Si0.3Ge0.7 modulation-doped (MOD) heterostructures with very high room-temperature mobility (1700cm2/Vs) 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) (1×105cm−2), small surface roughness (1–3 nm), and almost total relaxation (>95%), which were far superior to those of compositionally graded buffer layers (TDD: 107cm−2, surface roughness: >10 nm). The effect of the Ge/SiGe interface roughness in both kinds of LT buffer layers on the mobility was studied.