Development of new characterisation technique for interface states beyond bandgap

Interface state density is a key property for MOS devices in process development, material selection, and device simulation. Early attentions were focused on interface states within the bandgap of silicon. The interface states beyond bandgap (SBB) are often implicitly assumed to be negligible, but this is not experimentally verified. The existing techniques cannot probe SBB and the objective of this work is to develop a new characterisation technique for SBB. Based on a pulse capacitance voltage measurement, we will show that SBB can reach the order of 10¹³cm^-2eV^-1 and their neglect leads to a substantial underestimation of channel carrier mobility. The SBB are extrinsic and these results open the way to the exploration of their origin and suppression through process optimisation.