| Summary: | The electrical and physical properties of atomic layer deposition high-k (Al<sub>2</sub>O<sub>3</sub> and HfO<sub>2</sub>) /In<sub>x</sub>Ga<sub>1-x</sub>As (x = 0.53, 0.7, and 1) MOS interfaces with (NH<sub>4</sub>)S<sub>y</sub>, BHF, and HF pretreatment are examined. It is found that, as the In content (x) becomes higher, In<sub>x</sub>Ga<sub>1-x</sub>As MOS interfaces with BHF and HF cleaning show better C-V characteristics and lower interface state density (D<sub>it</sub>) than with (NH<sub>4</sub>)S<sub>y</sub> pretreatment. Also, the amounts of arsenic oxides, evaluated by X-ray photoelectron spectroscopy, at the high In content Al<sub>2</sub>O<sub>3</sub>/In<sub>x</sub>Ga<sub>1-x</sub>As MOS interfaces are found to increase with BHF and HF cleaning than with (NH<sub>4</sub>)S<sub>y</sub> cleaning. These results suggest that arsenic oxides can contribute to passivation of high-k/In<sub>x</sub>Ga<sub>1-x</sub>As MOS interface defects and the decrease in D<sub>it</sub> for x = 0.7 and 1. Finally, we propose a physical model to explain the relationship between possible interface defects responsible for D<sub>it</sub> and the pretreatment effects with the different In contents.
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