GaAs passivation by low-frequency plasma-enhanced chemical vapour deposition of silicon nitride

Passivation of GaAs by silicon nitride (Si_xN_y) deposition using low-frequency PECVD (LF PECVD) is presented. The high amount of hydrogen implantation during this process enhances the passivation effect, demonstrating for the first time the unpinning of the Fermi level by a simple deposition of Si_xN_y on a deoxidised GaAs surface. The (NH₄)₂S/Si_xN_y passivation is also simplified, and MIS capacitors are fabricated by a novel process, which consists in exposing the GaAs surface directly to sulphur solution, without the usual deoxidation etching step, followed by the deposition of LF PECVD Si_xN_y. Good modulation of the surface potential is observed, and the interface state density (D_it) as measured from 1 MHz C-V characteristics has a minimum of 3×10¹¹ cm^-2 eV^-1.