Capture cross section: A variable duty cycle charge pumping study

The performance and reliability of any transistor structure is largely dominated by the presence of interface and/or near interface defects. Monitoring the presence, quantity, and nature of these defects has been the topic of countless research efforts spanning a wide variety of measurement techniques (charge pumping, conductance, etc.). These measurements are very often used to extract defect capture cross section values and, in most cases, assign them as intrinsic properties of the defect [1]-[10]. It is however extremely troubling that the interface state capture cross section values reported for the most basic and well understood material system (Si/SiO2) ranges (Fig. 1) from 10^-12 cm²-10^-23 cm² [1]-[10]. Considering this unsettlingly broad range of values, it is quite tempting to discount the reported values as mere fitting parameters. In this study we perform a variant on charge pumping (CP), that we call variable duty-cycle charge pumping (VDC-CP) [11] which provides a direct and simple physics interpretation of the interface state capture process while retaining the high sensitivity of conventional CP. The results are interpreted using transition state theory to extract defect energy levels without any assumption of a capture cross section. The extracted energy levels are in excellent agreement with those measured directly using a spectroscopic CP technique, proving the utility of VDC-CP as well as the validity of applying the transition-state theory to measured kinetic data. This successful methodology is then used to explain why capture cross section is not an inherent property of interface defects and does not provide insight into the governing physics of charge capture [12].