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)(2)S-x] treatment prior to regrowth. Reflection high-energy electron diffraction observations indicate that GaAs native oxide is removed by this treatment at a 500 degrees C substrate temperature. This is 100 degrees 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)(2)S-x-treated interface is 1.8 x 10(-6) Omega cm(2), while it is 6.0 x 10(-5) Omega cm(2) without this treatment. Capacitance-voltage measurement and secondary-ion mass spectroscopy shaw 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 x 10(18) cm(-3)); therefore, they compensate impurities such as carbon or oxygen in the interface. These results reveal that (NH4)(2)S-x-treatment before regrowth is useful for improving device performances; that is, reducing source resistance for field-effect transistors fabricated by n(+)-GaAs selective growth.