Electrophysical properties of the MOS structure. II - Surface states

Research on the surface states of MOS structures and devices is reviewed. Surface states are classified and their general properties are outlined. A physicochemical interpretation of surface states is put forward, with oxygen vacancies seen as the most probable charge source. Oxygen vacancies are responsible for two energy levels identified with peaks on the state density distribution curve. The effect of crystal lattice orientation, of oxide formation, and of heating on surface states is analyzed. The relationship between surface states and the crystal lattice (Tamm states in the case of discontinuous lattice structures), boundary layer structure defects (oxygen or silicon vacancies), or the charge on oxide or other impurities is dealt with. The constant charge of surface states, trapping center instability, and fast surface states, and the amphoteric behavior of surface states, are discussed.