Re-examination of effects of sulfur treatment on Al2O3/InGaAs metal-oxide-semiconductor interface properties

Abstract

The effects of wet chemical treatments before treatment using (NH4)2S solutions in atomic layer deposition Al2O3/InGaAs metal-oxide-semiconductor (MOS) interfaces are experimentally examined. It is found that no chemical treatment before sulfur passivation leads to high interface state density (Dit) in spite of the (NH4)2S treatment. Furthermore, the value of Dit is dependent among the pretreatments using NH4OH, HCl, and BHF solutions before the sulfur treatment. HCl + (NH4)2S and BHF + (NH4)2S combinations show the lowest values of Dit. In addition, all of the Al2O3/InGaAs MOS interfaces with the sulfur treatment show a small amount of arsenic oxide. Thus, much higher Dit of the interfaces with the sulfur treatment indicates that the amount of arsenic oxide is not a deterministic factor for Dit. On the other hand, the amount of arsenic oxide before the sulfur treatment is found to correlate with Dit after sulfur treatment. Also, the interfaces with higher Dit after the sulfur treatment show a larger number of sulfur atoms remaining at the interfaces. These experimental results mean that there is a strong correlation among Dit, the amount of arsenic oxide, and the number of sulfur atoms remaining at the Al2O3/InGaAs interfaces. As a result, we can interpret for the present experimental results that the sulfur treatment can have two opposite impacts on Dit at the Al2O3/InGaAs interfaces: the decrease in Dit due to etching of native oxides and suppression of oxidation by sulfur passivation and the increase in Dit due to defect generation through some interaction between sulfur and arsenic oxide.