Two dimensional (2D) MoS2/ZnS heterojunctions with MoS2 thickness varying from monolayer to bulk have been prepared by sulfurization of a controlled thickness of Mo deposited on the ZnS thin films. Kelvin probe force microscopy measurements on MoS2/ZnS junction having varying thicknesses of MoS2 layers are carried out in the surface and junction modes, under white light exposure. Differences in the surface potential values of the surface and junction modes represent interface photovoltages at heterojunctions. Enhanced interface photovoltage is observed in junctions having the mono and few layer MoS2 in comparison to bulk MoS2 layer. This suggests the active participation of 2D MoS2 layer in photon absorption and charge separation processes taking place close to the junction. The present study is an effort towards the integration of 2D layered materials with 3D semiconductors, which may be advantageous for the development of 2D material based optoelectronic devices.

The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained.

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In the present work, photoanodic response of ZnTe thin films is enhanced by incorporating oxygen, which is explained by analyzing oxygen-induced modifications in structural, optical, and electronic behavior of ZnTe thin films, using detailed experimental characterizations and density functional theory (DFT) based calculations. On incorporating oxygen, the nanocrystalline character of ZnTe is increased with a change in optical properties due to absorption through sub band states and an increase in fundamental absorption edge. From DFT analysis, origin of these sub band gap states is attributed to oxygen incorporation induced electronic states and Te vacancies. Photoelectrochemical (PEC) performances of ZnTe with and without oxygen have been investigated where a change over from photocathodic response for ZnTe to enhanced photoanodic response for ZnTe:O thin films along with increased response for low energy photons is observed. These findings are explained in terms of oxygen induced modification in visible light absorption, enhanced surface area due to increased nanocrystalline character and modified electronic properties of ZnTe:O thin films. Modifications in optical properties and enhancement in PEC performance by oxygen incorporation shown in the present study may be useful for developing ZnTe-based photovoltaic devices.

Structural, optical, and surface potential properties of CdSe nanoparticles (NPs) prepared on ZnS thin-films have been investigated. CdSe NPs/ZnS thin-films with varying CdSe NPs diameters are synthesised by sequential radio frequency magnetron sputtering technique. A blue shift in the optical absorption edge and enhancement in the optical constants are observed with decrease in the nanoparticles size. CdSe NPs/ZnS thin-films show an absorption edge at about 3.5 eV corresponding to ZnS and another size dependent absorption edge in the energy range of 1.74–2.16 eV, corresponding to CdSe NPs. Decrease in photoluminescence (PL) intensity of ZnS film on incorporation of CdSe NPs is observed; however, no distinct emission peaks corresponding to NPs are seen. Multilayered CdSe NPs/ZnS thin-films comprising of six alternating layers show PL signature both due to ZnS and CdSe NPs. Kelvin probe force microscopy (KPFM) studies show that surface potential values of CdSe NPs/ZnS thin-films lie in between that of ZnS (209 meV) and CdSe/ZnS (−4 meV) thin-films, which confirms charge transfer between CdSe NPs and ZnS thin-films. The evolution of CdSe NPs/ZnS nanoscale heterojunction has been observed with shift in the surface potential values by varying size and coverage of CdSe NPs.