Orientation Dependence of the Low Field Mobility in Double-and Single-gate SOI FETs

The low field mobility in double- and single-gate structures is analyzed for (100) and (110) SOI substrate orientation. Due to volume inversion, mobility in double-gate ultra-thin body (110) SOI FETs is enhanced in comparison with the mobility of single-gate structures in the whole effective field range. In double-gate (100) structures the mobility decreases below the single-gate value for high effective fields. It is argued that the twice as high carrier concentration in double-gate FETs causes significant occupation of higher subbands, where mobility is low, and that additional intersubband scattering channels for the lowest subband are opened. These effects partly compensate the mobility enhancement due to volume inversion and lead to a mobility decrease in double-gate (100) structures