A study of noise in surface and buried channel SiGe MOSFETs with gate oxide grown by low temperature plasma anodization

A study is made of noise in p- and n-channel transistors incorporating SiGe surface and buried channels, over the frequency range f=1 Hz–100 kHz. The gate oxide is grown by low temperature plasma oxidation. Surface n-channel devices are found to exhibit two noise components namely 1/f and generation–recombination (GR) noise. It is shown that the 1/f noise component is due to fluctuations of charge in slow oxide traps whilst bulk centers located in a thin layer of the semiconductor close to the channel, give rise to the GR noise component. The analysis of the noise data gives values for the density D_ot of the oxide traps in the SiGe and Si nMOSFETs of the order 1.8×10¹² and 2.5×10¹⁰ cm^?2 (eV)^?1, respectively. The density D_GR of the bulk GR centres is equal to 3×10¹⁰ cm^?2 in both the SiGe and Si devices. The electron and hole capture cross-sections for these centres as well as their energy level and their depth below the oxide/semiconductor interface are also the same in the devices of both types. This suggests that those GR centers are of the same nature in all devices studied. p-Channel devices show different behaviour with only a 1/f noise component apparent in the data over the same frequency range. Buried SiGe channel and Si control devices exhibit quite low and similar slow state densities of the order low to mid 10¹⁰ cm^?2 (eV)^?1 whereas surface p-channel devices show even higher slow state densities than n-channel counterparts. The Hooge noise characterized by the Hooge coefficient _H=2×10^?5 is also detected in some buried p-channel SiGe devices.