Improvement of Atomic-Layer-Deposited Al₂O₃/GaAs Interface Property by Sulfuration and NH₃ Thermal Nitridation

Fermi level pinning at the interface between high-k gate dielectric and GaAs induced by unstable native oxides is a major obstacle for high performance GaAs-based metal-oxide-semiconductor (MOS) devices. We demonstrate the improved Al₂O₃/GaAs interfacial characteristics by (NH₄)₂S immersion and NH₃ thermal pretreatment prior to Al₂O₃ deposition. X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfuration of GaAs surface by (NH₄)₂S solution can effectively reduce As-O bonds while Ga-O bonds and elemental As still exist at Al₂O₃/GaAs interface. However, it is found that N incorporation during the further thermal nitridation on sulfurated GaAs can effectively suppress the native oxides and elemental As in the sequent deposition of Al₂O₃. Atomic force microscopy (AFM) shows that the further thermal nitridation on sulfurated GaAs surface can also improve the surface roughness.