Atomic Layer Deposition of Ga<sub>2</sub>O<sub>3</sub> from GaI<sub>3</sub> and O<sub>3</sub>: Growth of High-Density Phases
Lauri Aarik, Hugo Mändar, Jekaterina Kozlova, Aivar Tarre, Jaan Aarik
Abstract
Gallium oxide thin films, containing either α-Ga 2 O 3 or κ-Ga 2 O 3 crystalline phases, were grown by atomic layer deposition (ALD) by using GaI 3 and O 3 as precursors. The κ-Ga 2 O 3 phase was observed in the films grown on Si(1 0 0) at substrate temperatures ≥450 °C, while α-Ga 2 O 3 was obtained at temperatures ≥275 °C on α-Cr 2 O 3 seed layers deposited on Si(1 0 0). The seed layers with thicknesses down to 0.7 nm appeared to be sufficient to initiate the α-Ga 2 O 3 growth. The densities of 5.2–5.3 g/cm 3 for amorphous films deposited at the substrate temperatures 150–234 °C, 5.9−6.1 g/cm 3 for the films deposited on uncoated Si substrates at 450–550 °C, and 6.3−6.4 g/cm 3 for the films deposited on α-Cr 2 O 3 seed layers at 350–550 °C were determined from X-ray reflectometry measurements. The growth per cycle decreased from 0.17 to 0.05–0.09 nm with the growth temperature increase from 150 to 550 °C. Notably, the growth rates of α-Ga 2 O 3 films on α-Cr 2 O 3 seed layers were significantly higher at 350–450 °C than those of the films deposited on uncoated Si at the same temperatures, indicating that crystal structure influenced the growth per cycle in this ALD process. The concentration of iodine impurities did not exceed 3.2 at. % in the films deposited at 150 °C. With the growth-temperature increase to 350 °C, the concentration of impurities decreased to ≤0.04 at. % in the films grown on bare Si and ≤0.01 at. % in the films grown on α-Cr 2 O 3 seed layers.