GaAs surface chemical passivation by (NH4)(2)S+Se and the effect of annealing treatments

We report on a new Se chemical passivation [(NH4)(2)S+Se] for GaAs surfaces. We compare our Se passivated surfaces with (NH4)(2)S+S [(NH4)(2)S-x] passivated surfaces by preparing Al-nGaAs Schottky diodes and submitting them to cumulative annealing treatments. We find that with or without an annealing treatment the Schottky barriers are consistently closer to the ideal value (0.2 eV) when the GaAs surfaces are treated with the (NH4)(2)S+Se rather than the (NH4)(2)S-x chemical solution. This indicates that (NH4)(2)S+Se surface passivation is more effective in reducing the surface state density and in unpinning the Fermi level than the (NH4)(2)S-x passivation treatment. These results are attributed to the complementary passivation role of the S and the Se on the GaAs surface. Also, the annealing treatment plays an important role in the control of the barrier height in both kinds of passivation.