Evidence of a high density of fixed negative charges in an insulation layer compound on silicon

Fur drift field generation. IS structures with a positive interface charge in an insulator compound were developed in the 1980s and employed mainly on field effect solar cells. While there has been a large number of publicati ons about the positively biased insulator-semiconductor structure there has been very little interest in its antipolar counterpart - the negatively bi ased insulator-semiconductor structure so far. However. by using that struc ture as a second drift field source for field effect solar cells their conv ersion efficiency could be improved. The conventional rear surface passivat ion of silicon active layers by shallow ultrahigh aluminium doping in order to form a back surface field involves a high density of lattice and surfac e defects which increase recombination rates. The structure introduced here in is put onto a silicon layer and acts thus as an external negative drift field source, thereby avoiding the drawbacks of ultrahigh doping. The layer arrangement aluminiumfluoride-silicon dioxide on silicon seems to be a goo d candidate for a negative drift field source. Experimental results which l ed to a fixed interface charge of up to - 1.6 x 10(12) cm(-2) at the interf ace aluminiumfluoride parallel to silicon dioxide are presented and an inte rpretation of the fixed negative charge is given. (C) 2001 Elsevier Science B.V. All rights reserved.