Gallium-containing sulfide binary and ternary materials by atomic layer deposition: precursor reactivities and growth fine chemistries

Gallium sulfide (GaxS) and copper gallium sulfide (CuxGaySz) were synthetized by atomic layer deposition (ALD), using copper acetylacetonate Cu(acac)2, hexakis(dimethylamino)digallium [Ga(NMe2)3]2 and hydrogen sulfide (H2S). Thanks to the compatibility of the CuxS and GaxS ALD windows, a supercycle strategy that combines single growth cycles of the two binary compounds was used to generate the ternary material. A wide range of compositions and properties can be obtained from Ga-rich to Cu-rich via copper gallium sulfide thin films. Structural, morphological, and optoelectronic characterizations were performed on all films. Surface and in-depth chemical compositions were determined by X-ray photoelectron spectroscopy profiling, allowing a better understanding of the chemical reactions involved during the growth process. In the case of GaxS films, other Ga precursors have been tested. Our experimental observations, combined with reported ones and density functional theory calculation results have highlighted the specific reactivity of alkylamido precursor in ALD chemistry. Compositional studies revealed a significant O content which origin is discussed and represents an important challenge to address in ALD of sulfide materials in general.