Mechanisms of GaAs surface passivation by a one-step dry process using low-frequency plasma enhanced chemical deposition of silicon nitride

Abstract III-V materials are known for their high surface states densities which degrade the performances of photonic and electronic devices. Plasma-enhanced chemical vapor deposition of SixNy is commonly used to passivate surface states and to encapsulate III-V devices and circuits. The plasma is generated with an RF excitation source usually set at a high frequency of 13.56 MHz. To obtain a high quality III-V/SixNy interface, many chemical surface treatments are required before deposition, as well as post-deposition thermal annealing. In this work, we demonstrate that a low-frequency plasma allows for an efficient passivation process by a simple deposition of SixNy, without any wet chemical pretreatment nor post-deposition annealing. This dry process is more compatible with the passivation and encapsulation of completed III-V devices and circuits. Metal-insulator-semiconductor capacitors were fabricated by depositing SixNy on GaAs at a frequency of 90 kHz. C V measurements indicated the unpinning of the Fermi level and a low density of surface states in the mid 1011 cm−2 eV−1 range. X-ray photoelectron spectra have shown the complete suppression of native oxides and an important reduction of elemental arsenic from the GaAs surface. The mechanisms of surface passivation by ionic hydrogen bombardment inherent to the low-frequency plasma deposition of SixNy are discussed.