Electron Mobility Degradation Due to Remote Coulomb Scattering in Ge MOSFET

Abstract

Remote Coulomb scatterings (RCS) on electron mobility degradation are experimentally investigated in Ge based metal-oxide-semiconductor field-effect-transistor (MOSFETs) with GeOx/Al2O3 gate stacks. The mobility is found increased with thicker GeOx (7.8-20.8 A). The physical origin of this mobility dependence on GeOx thickness is explored. The following factors are excluded: Coulomb scattering due to interfacial traps at GeOx/Ge, phonon scattering, and surface roughness scattering. Therefore, the RCS from charges in gate stacks are studied. The charge distributions in GeOx/Al2O3 gate stacks are experimentally evaluated. The bulk charges in Al2O3 and GeOx are found negligible. The density of interfacial charge is +3.2×10 cm at GeOx/Ge interface, and -2.3×10 cm at Al2O3/GeOx interface. The electric dipole at Al2O3/GeOx interface is found +0.15 V, corresponding to areal charge density of 1.9×10 cm. The origin of this mobility dependence on GeOx thickness is attributed to the RCS due to electric dipole at Al2O3/GeOx interface. And this remote dipole scattering is found to play a significant role on mobility degradation. The discovery of this new scattering mechanism indicates that engineering of Al2O3/GeOx interface is key for mobility enhancement and device performance improvement. These results are helpful for understanding and engineering the Ge mobility enhancement. Keywords—Ge; Mobility; Remote Coulomb scatterings;