A study was made of intrinsic and generated bulk defects, in the gate insulator of field-effect transistors, by using a forward-bias pulse technique to inject up to 1017 electrons per cm2 at 293 and 100K. The insulator thicknesses ranged from 5.4 to 50.5nm. The amount of trapping that was observed at 100K was some 30 times greater than that detected at 293K. An additional trapping at low temperatures was attributed to 2 causes. One of these was trapping by existing shallow bulk defects, and the other was an increase in the density of generated bulk defects. It was proposed that the defect generation process was related to an instability of the neutral hole trap during injection. This produced an electron trapping effect. This instability appeared to increase as the temperature was reduced to 100K. This was attributed to a “freeze out” effect, or to higher-energy carriers that resulted from a reduction in thermal scattering. The defect generation rate obeyed a power law, such that the rate of defect generation depended upon the injection current density. The charge centroid of the resultant defects, as measured from the substrate/oxide interface, was determined at both temperatures. The centroid of shallow electron traps was determined at 100K. The centroids were found to be between 6 and 8nm at 100K and between 10 and 16nm at 293K. A defect-free (so-called tunnelling) region of 2 to 4nm was shown to exist at each interface. It was noted that the shallow traps could be rapidly depopulated by subjecting the samples to white light.

H.S.Kim, C.K.Williams, A.Reisman: Journal of Applied Physics, 1997, 81[3], 1566-74