TIME-DEPENDENT CHARGING BY X-RAY-IRRADIAT ION OF ULTRATHIN SIO2-FILMSON SI

In the study of X-ray-induced surface potential changes of ultrathin S iO2 films on Si caused by X-ray irradiation, Ne investigated why the t ime constant for the X-ray-irradiation time dependence decreases with increasing oxide thickness and saturates at about 10 nm thickness. We conclude that the above changes are caused by the hole trapping at tra ps dose to the SiO2/Si interface and that the time constant is greater at small thicknesses because the hole concentration is effectively sm aller at thicknesses close to the hole mean free path, which could be estimated to be about 1.8 nm.