Passivation of GaAs metal–insulator–semiconductor structures by (NH4)2Sx and by evaporation of SiO2

Al–SiO 2 – GaAs structures are prepared and characterized by electrical measurements. The GaAs (100) surfaces are cleaned and passivated by chemical solutions. A passivation treatment based on ammonium polysulfide (NH4)2Sx is applied, then an insulating layer is deposited by electron-beam evaporation of an amorphous SiO2. By adjusting the passivation and the insulator deposition parameters, the accumulation and inversion conditions are observed by a capacitance–voltage (C–V) technique, showing that the Fermi level is unpinned. The interface-states density Dit as calculated using the method of Terman applied to high-frequency C–V characteristics presents a minimum of 1011 cm−2 eV−1.