1/f Noise and trap density in n-channel strained-Si/SiGe modulation doped field effect transistors

The low frequency (1/f) noise characteristics of Schottky-gated strained-Si n-channel modulation doped field effect transistors have been investigated as a function of Ge concentration for different virtual substrates. The gate voltage dependence of the 1/f noise agrees well with the McWhorter carrier number fluctuations model. The trap density (extracted using a Ge dependent potential barrier height and tunnelling constant) is low in devices on thick virtual substrates (Nt = (2–6) × 1016 cm−3 eV−1), and does not degrade with the increase of the Ge concentration from 30% to 40%. This trap density is the same for thin Helax virtual substrates (He+ ions implanted thin substrate) but increases two orders of magnitude for thin low-temperature grown substrates.