1/f noise in Si and Si0.7Ge0.3 pMOSFETs

Strained layer Si_0.7Ge_0.3 pMOSFETs were fabricated and shown to exhibit enhanced hole mobility, up to 35% higher for a SiGe device with 3-nm-thick Si-cap, and lower 1/f noise compared to Si surface channel pMOSFETs. The 1/f noise in the investigated devices was dominated by mobility fluctuation noise and found to be lower in the SiGe devices. The source of the mobility fluctuations was determined by investigating the electric field dependence of the 1/f noise. It was found that the SiO₂/Si interface roughness scattering plays an important role for the mobility fluctuation noise, although not dominating the effective mobility. The physical separation of the carriers from the SiO₂/Si interface in the buried SiGe channel pMOSFETs resulted in lower SiO₂/Si interface roughness scattering, which explains the reduction of 1/f noise in these devices. The 1/f noise mechanism was experimentally verified by studying 1/f noise in SiGe devices with various thicknesses of the Si-cap. A too large Si-cap thickness led to a deteriorated carrier confinement in the SiGe channel resulting in that considerable 1/f noise was generated in the parasitic current in the Si-cap. In our experiments, the SiGe devices with a Si-cap thickness in the middle of the interval 3-7 nm exhibited the lowest 1/f noise.