EFFECT OF POST-THERMAL ANNEALING ON THE VARIOUS SULFUR PASSIVATIONS OF GAAS

Effects of post-thermal annealing on the various sulfur passivations of GaAs were investigated using X-ray photoelectron spectroscopy (XPS) and electrical measurements of the Schottky diode. The P2S5/NH4OH, (NH4)(2) S-x and Na2S solutions were used as sulfur sources. The XPS data showed that thermal annealing after any of the passivations studied here, substantially decreased the amounts of both elemental arsenic (As-0) and unstable As-S bonds (probably incomplete compounds such as AsS). On the other hand, the amount of stable Ga-S bonds increased after post-thermal annealing for all the sulfur passivations studied here. These findings show that unstable As-S bonds were converted to stable Ga-S bonds during post-thermal annealing. This behavior was the most marked in the Na2S passivation. Elemental arsenic, As suboxides such as AsO and incomplete As-S bonds are considered to be detrimental to the formation of stable GaAs surface, whereas the full-oxides of both As and Ga (As2O3 and Ga2O3) and probably the full-sulfide (As2S3) are not so detrimental. The electrical characteristics were also observed to be considerably improved by the post-thermal annealing. Degradations of electrical characteristics were smallest for the sample annealed after P2S5/NH4OH passivation (and cleaning in deionized water). The P2S5/NK4OH treatment leads to the most robust surface passivation of GaAs among those studied here.