Applicability of Charge Pumping on Germanium MOSFETs

In this letter, the charge-pumping (CP) technique is validated for germanium MOSFETs. Effects of the smaller Ge bandgap on CP are discussed through both experiments and simulations. The standard CP setup with ~ 100-ns transition times at room temperature tuned for Si/SiO₂ MOS evaluates the Ge interface-trap density only near midgap, and the total density is thus strongly underestimated. We show two CP methods which can be used to correctly reflect the actual complete interface-trap density by probing closer to the band edges. The use of low-temperature measurements to probe traps near the band edges with CP is discussed. CP measurements are demonstrated with transition times down to 6-ns at 300-K without making use of RF structures. Using these fast measurements, it is possible to obtain an interface state density closer to the band edges for Ge MOSFETs at 300-K.