Effect of O2 plasma exposure time during atomic layer deposition of amorphous gallium oxide

Amorphous gallium oxide thin films were grown by plasma-enhanced atomic layer deposition on (100) silicon substrates from trimethylgallium Ga(CH3)3 precursor and oxygen plasma. At 200 °C, the growth per cycle is in the range of 0.65–0.70 Å for O2 plasma exposure times ranging from 3 up to 30 s during each cycle. The effect of O2 plasma exposure times on the interfacial SiOx regrowth and the electrical properties was investigated. In situ spectroscopic ellipsometry shows that the SiOx regrowth occurs during the first three cycles and is limited to 0.27 nm for plasma times as long as 30 s. Increasing the O2 plasma exposure during each ALD cycle leads to a drastic decrease in the leakage current density (more than 5 orders of magnitude for 30 nm films), which is linked to the suppression of oxygen vacancy states as evidenced by spectroscopic ellipsometry. Interestingly, an increase in the dielectric constant with increasing O2 plasma exposure time is observed, reaching a value of ε r ∼ 14.2, larger than that of single crystalline β-Ga2O3. This study highlights the crucial role of oxygen plasma exposure time in the control and tuning of the electrical properties of amorphous gallium oxide films.