Low-frequency noise and Coulomb scattering in Si0.8Ge0.2 surface channel pMOSFETs with ALD Al2O3 gate dielectrics

Carrier mobility and low-frequency noise were investigated in Si0.8Ge0.2 surface channel pMOSFETs with ALD Al2O3 gate dielectrics. The devices were annealed in H2O vapor, which reduced the negative charge in the gate dielectrics. The carrier mobility was characterized versus change in oxide charge, which allowed an estimation of the Coulomb scattering from the charge in the Al2O3. The low-frequency noise was measured between subthreshold and strong inversion conditions in the H2O annealed and the un-annealed devices. The combined number fluctuation and correlated mobility fluctuation noise model could successfully explain the observed 1/f noise. The mobility fluctuations were negatively correlated to the number fluctuations in the un-annealed devices, which contained a negative oxide charge. In the H2O annealed devices, on the other hand, a positive correlation could be observed. The maximum magnitude of the scattering parameter α was found to be around 1×104Vs/C. The H2O annealing was used in this work as a non-destructive tool to modify the charge in the Al2O3, but it can also be a viable method to improve device performance by introducing/passivating charge.