Atomic Layer Deposition of In₂O₃:H from InCp and H₂O/O₂: Microstructure and Isotope Labeling Studies

The atomic layer deposition (ALD) process of hydrogen-doped indium oxide (In₂O₃:H) using indium cyclopentadienyl (InCp) and both O₂ and H₂O as precursors is highly promising for the preparation of transparent conductive oxides. It yields a high growth per cycle (>0.1 nm), is viable at temperatures as low as 100 °C, and provides a record optoelectronic quality after postdeposition crystallization of the films ( ACS Appl. Mat. Interfaces , 2015 , 7 , 16723 - 16729 , DOI: 10.1021/acsami.5b04420 ) . Since both the dopant incorporation and the film microstructure play a key role in determining the optoelectronic properties, both the crystal growth and the incorporation of the hydrogen dopant during this ALD process are studied in this work. This has been done using transmission electron microscopy (TEM) and atom probe tomography (APT) in combination with deuterium isotope labeling. TEM studies show that an amorphous-to-crystalline phase transition occurs in the low-temperature regime (100-150 °C), which is accompanied by a strong decrease in carrier density and an increase in carrier mobility. At higher deposition temperatures (>200 °C), enhanced nucleation of crystals and the incorporation of carbon impurities lead to a reduced grain size and even an amorphous phase, respectively, resulting in a strong reduction in carrier mobility. APT studies on films grown with deuterated water show that the incorporated hydrogen mainly originates from the coreactant and not from the InCp precursor. In addition, it was established that the incorporation of hydrogen decreased from ∼4 atom % for amorphous growth to ∼2 atom % after the transition to crystalline film growth.