AN IMPROVED TECHNIQUE AND EXPERIMENTAL RESULTS FOR THE EXTRACTION OF ELECTRON AND HOLE MOBILITIES IN MOS ACCUMULATION LAYERS

For the first time, experimental results are presented for electron an d hole mobilities In the electron and hole accumulation layers of a MO SFET for a wide range of doping concentrations. Also presented is an i mproved methodology that has been developed in order to enable more ac curate extraction of the accumulation layer mobility, The measured acc umulation layer mobility for both electrons and holes is observed to f ollow a universal behavior at high transverse electric fields, similar to that observed for minority carriers in MOS inversion layers. At lo w to moderate transverse fields, the effective carrier mobility values are greater than the hulk mobility values for the highest doping leve ls. this is due to screening by accumulated carriers af the ionized im purity scattering hy accumulated carriers, which dominates at higher d oping concentrations, For lower doping levels, surface phonon scatteri ng is dominant at low to moderate transverse fields so that the carrie r mobility is below the bulk mobility value.