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Improvement in Electrical Properties at an n-GaAs/n-GaAs Regrown Interface Using Ammonium Sulfide Treatment

Electrical properties in an n-GaAs/n-GaAs interface regrown by molecular beam epitaxy (MBE) were remarkably improved using ammonium sulfide [(NH4)2Sx] treatment prior to regrowth. Reflection high-energy electron diffraction observations indicate that GaAs native oxide is removed by this treatment at a 500°C substrate temperature. This is 100°C lower than the temperature for removal of a native oxide by conventional thermal annealing in MBE. Transmission line model measurement shows that contact resistance at the (NH4)2Sx-treated interface is 1.8×10-6 Ωcm2, while it is 6.0×10-5 Ωcm2 without this treatment. Capacitance-voltage measurement and secondary-ion mass spectroscopy show that this reduction, in contact resistance at the regrown interface, is due to sulfur atoms in the interface behaving as donors (at a carrier concentration of 2×1018 cm-3); therefore, they compensate impurities such as carbon or oxygen in the interface. These results reveal that (NH4)2Sx-treatment before regrowth is useful for improving device performances; that is, reducing source resistance for field-effect transistors fabricated by n+-GaAs selective growth.