Optical properties and band alignments in ZnTe nanoparticles/MoS₂ layer hetero-interface using SE and KPFM studies

Integration of a layered two-dimensional (2D) material with a non-2D material provides a platform where one can modulate and achieve the properties desired for various next-generation electronic and opto-electronic applications. Here, we investigated ZnTe nanoparticles/MoS₂ hetero-interfaces with the thickness of the MoS₂ varying from few to multilayer. High-resolution transmission electron microscopy was used to observe the crystalline behaviour of the ZnTe nanoparticles, while the number of MoS₂ layers was investigated using Raman measurements. Spectroscopic ellipsometry (SE) analysis based on the five-layer fitting model was used to analyse the optical behaviour of the heterojunction, where the excitonic features corresponding to the MoS₂ layers and absorption features due to the ZnTe nanoparticles are observed. From the Kelvin probe force microscopy (KPFM) measurements, the surface potential (SP) of the ZnTe nanoparticles/MoS₂ is found to be different in comparison with the SP of the ZnTe nanoparticles and MoS₂, which is indicative of the charge transfer at the ZnTe nanoparticles/MoS₂ hetero-interface. Various parameters obtained using SE and KPFM measurements were used to propose energy band alignments at the ZnTe nanoparticles/MoS₂ hetero-interface. In addition, an interface photovoltage of 193 mV was obtained by carrying out KPFM measurements under illuminating condition. (paper)