EVALUATION OF ELECTRON TRAP LEVELS IN SOI BURIED OXIDES BY TRANSIENT PHOTOCURRENT SPECTROSCOPY

An electron trap density of 2 x 10(15) cm(-3) in a buried oxide of sil icon-on-insulator structure is detected by transient photocurrent spec troscopy. Through the two-step photodepopulation method, the distribut ion of electron trap level was found to have a peak at 2.3 eV below th e oxide conduction band edge. The capture cross section of 8.8 x 10(-1 4) cm(2) meant that the electron traps are positively charged centers. Flatband shift measurement indicates that pre-existing positive charg es in the oxide are compensated for by photoelectron injection. These results suggest that the pre-existing positive charges and the electro n traps have an identical origin.