Distinction between donor and acceptor character of surface states in the Si-SiO2 interface

The charge type of interface states is determined utilizing surface potential fluctuations. For thermally grown (111) -oriented n-type silicon, it is shown that the surface states below the conduction band are only donor states. Within the conduction band, an upper limit of 5×1011 possible donor states per cm2 is found. Within and above the valence band, acceptor states are either absent or at most present at a lower level than donor states. An upper limit of 1.6×1011 possible acceptor states per cm2 is obtained in this energy region.