Surface preparation and effective contact formation for GaAs surface

(NH₄)₂S solution was applied to surface-cleaned (etched) GaAs using various kinds of solution and method to investigate the passivation mechanism. After cleaning with HCl and ₃PO₄, elemental As remained on GaAs surface and successive sulfidation treatments resulted in the formation of As-S bond. However, there was no As-S bond observed after the sulfidation of NH₄OH-cleaned GaAs because elemental As was dissolved in NH₄OH solution. The thermally cleaned GaAs surface at 600°C containing a large amount of elemental Ga on surface showed the formation of Ga-S bond after sulfidation treatment. Therefore, it could be confirmed that the elemental forms of As and Ga bind with S and produce Ga-S and As-S bonds, which induce the passivation effect on GaAs. A new technique using sulfidation and subsequent hydrogenation treatment was studied to minimize defective interfacial bonds of metal(Pd, Au)/GaAs Schottky contact. Sulfur-passivation was effective to make metal/GaAs interface completely free of GaAs oxides, and hydrogenation treatment after the deposition of metal ultrathin film was introduced to control the defective As compounds originated from the metallization. After the treatment, the reverse leakage current of the Schottky diode was dramatically reduced about 10 times, compared with the simply S-passivated sample. Furthermore, from capacitance-voltage (C-V) dopant profile, these sulfidation and subsequent hydrogenation processes were found to cause no damage to the GaAs substrate.