• Faraji, Shirin
• Alsalhi, M.
• Barakat, F.
• Alterary, S.
• Laref, A.

Abstract

<p>The two-dimensional (2D) layered molybdenum disulfide (MoS₂) material represents a nominee potent for optoelectronic devices application. In this research work, the experimental characterizations of 2D- MoS₂ thin films are reported in terms of various microscopic and spectroscopic techniques. The synthesized MoS₂ thin films are grown by employing the pulsed laser deposition (PLD) procedure on SiO₂/Si substrates. In order to monitor the deposition rates of ablated films, the buffer argon-gas pressures are varied during the pulsed laser deposition at substrate temperature of 700 °C. The field emission scanning electron microscopy and atomic force microscopy analyzes revealed a change in the surface morphology of MoS₂ films when the buffer Ar-gas pressure is varied between 0 and 100 mTorr. For all samples, a 2H-phase is revealed from X-ray diffraction patterns, indicating a reflection (2θ) around 14.85°. By varying the deposition pressure of laser-ablated MoS₂ films, the X-ray photoelectron spectroscopy divulged the chemical compositional elements and valence states of Mo and S on the surface of MS₂ films with low density of defects. Analysis of the photoluminescence spectroscopy illustrated emission bands spanning from the visible (Vis) to near-infrared (NIR) regimes in the deposition pressures range ~ 0–100 mTorr. This is mainly owing to the change in the recombination of electron–hole pairs and charge transfer between the deposited MoS₂ films and SiO₂ substrate surface under various buffer gas pressures. Additionally, first-principles electronic structure calculations are performed to qualitatively examine the effect of native point-defect species (sulfur-monovacancy and sulfur-divacancy defects) on the electronic structure and optical properties of 2D- MoS₂ sheets. It is unveiled that the variation of compositional sulfur-vacancy defect in MoS₂ monolayer creates an in–gap defect levels above the valence states, leading to an acceptor character. Importantly, the enhancement in the optical absorption spectra divulged a shift in the optical gap from Vis-NIR window with the increase of sulfur vacancy contents in MoS₂ single-layer. The identification of intrinsic point defects may be beneficial for photovoltaic energy conversion at higher wavelengths by designing next generation 2D-semiconductors, which could be of vital significance for growing 2D layers and multilayers into practical technologies.</p>

Topics

• density
• impedance spectroscopy
• surface
• photoluminescence
• molybdenum
• phase
• scanning electron microscopy
• x-ray diffraction
• thin film
• x-ray photoelectron spectroscopy
• atomic force microscopy
• semiconductor
• layered
• mass spectrometry
• two-dimensional
• pulsed laser deposition
• vacancy
• point defect