To improve the stability and carrier mobility of quantum dot (QD) optoelectronic devices, encapsulation or pore infilling processes are advantageous. Atomic layer deposition (ALD) is an ideal technique to infill and overcoat QD films, as it provides excellent control over film growth at the sub-nanometer scale and results in conformal coatings with mild processing conditions. Different thicknesses of crystalline ZnO films deposited on InP QD films are studied with spectrophotometry and time-resolved microwave conductivity measurements. High carrier mobilities of 4 cm² (V s)⁻¹ and charge separation between the QDs and ZnO are observed. Furthermore, the results confirm that the stability of QD thin films is strongly improved when the inorganic ALD coating is applied. Finally, proof-of-concept photovoltaic devices of InP QD films are demonstrated with an ALD-grown ZnO electron extraction layer.

The aluminum precursor plays a crucial role in the Al₂O₃ ALD process. To date, trimethylaluminum (TMA) is one of the most widely used precursors in experimental and theoretical studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theoretical and experimental investigation is carried out on the Al₂O₃ ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The experimental results pointed out that the thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 Å/cycle at temperatures of 150 to 175 °C. On the basis of the in situ mass spectrometry analysis and DFT calculations, the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissociation occur. Design of heteroleptic precursors containing alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al₂O₃ ALD.