Understanding the crystallization mechanism of atomic layer deposited InOx/GaOx nanolaminate structures

We report the crystallization mechanism of InOx/GaOx nanolaminate structures deposited via the supercycle method of atomic layer deposition (ALD) and present a comparison with sputter-deposited Ga-doped In2O3 (IGO). IGO films deposited by ALD (ALD-IGO) with different Ga concentrations were deposited by controlling the InOx:GaOx subcycle ratio and were compared with sputter-deposited IGO (sputter-IGO) films with a uniform In and Ga distribution as a reference in terms of the crystallization temperature (Tc) and interdiffusion of the InOx/GaOx nanolaminate structure under annealing. The Tc of ALD-IGO thin films is more than 100 °C higher than sputter-IGO films under the same Ga concentrations from 7 to 19 at. %. Moreover, the relationship between the Ga concentration and the lattice constant (Lc) of the ALD-IGO and sputter-IGO films was evaluated and compared to discuss the substitution of Ga in the In sites of the In2O3 crystal. The sputter-IGO films follow Vegard’s law, and Lc decreases linearly with increasing Ga concentration. However, the relationship between Ga concentration and Lc in ALD-IGO with Ga concentrations over 12 at. % does not follow Vegard’s law, and the decrease in Lc with increasing Ga concentration is limited, suggesting that Ga substitution into In2O3 crystals is suppressed. These behaviors are attributed to the concentration distributions of In and Ga induced by the nanolaminate structure formed by ALD. We expect that an understanding of the crystallization mechanisms of InOx/GaOx nanolaminate structures will contribute to the development of integrated devices and guidelines for ALD conditions based on crystalline In2O3-related oxide semiconductor materials.