Electrical, Optical and Structural Characterization of Molybdenum Trioxide (MoO3) Nano Rods

Molybdenum trioxide (MoO3) is a promising material for various semiconductor devices due to its unique electrical and optical properties [1-3]. These attributes make it suitable for memristive or charge-trapping devices, which are key in non-volatile memory and neuromorphic computing applications. Here we focus on the deposition of MoO3 films via spin coating, characterizing the electrical, optical, and structural properties of MoO3, and its integration into charge-trapping devices, focusing on optimizing deposition parameters to achieve high-quality, uniform films suitable for charge-trapping applications.
MoO3 crystals were dispersed in isopropyl alcohol at three different concentrations (1g/L, 5g/L, and 10g/L) to create a stable dispersion. IPA's low viscosity and fast evaporation make it ideal for uniform film deposition via spin coating. To ensure the solution's homogeneity and prevent particle aggregation, the solution was sonicated for 90 minutes using a sonicator bath. Ensuring well-dispersed particles and consistent film coverage.
The MoO3 solution was deposited on silicon substrates of size 1.5x1.5 cm^2 and a solution volume of 10uL per layer. The deposition was conducted through spin coating, with rotational speeds ranging from 1200-2000 rpm to control film uniformity. Post-deposition, the films were characterized and tested for their different properties. Structural characterization of the films was performed using Raman to confirm the formation and existence of MoO3 crystals, while the SEM and AFM were employed to investigate surface morphology and film thickness and uniformity.
Significant clustering of the MoO3 occurs post-deposition at higher concentration (5g/L and 10g/L). Centrifuging at 5000 rpm for 30 min effectively reduced the aggregated crystals. Optical and electrical testing of the films was carried out using the UV-Vis and Hall Effect to analyze the material’s absorption, bandgap, conductivity and mobility. Our findings indicate that the spin coating process with the centrifuged solution results in more uniform MoO3 films with low surface clustering. The nanoparticles exhibited a mean thickness value of 20nm, which represents a 2D layer of MoO3. The films also exhibited a distinct absorption edge around 350 nm and a direct bandgap of approximately 3.2 eV for MoO3 on 3x3 cm^2 glass substrates. While the MoO3 solution exhibited a direct bandgap of approximately 3.6 eV. The carrier mobility for MoO3 deposited on silicon substrate was found to be an average of 1.8 × 10^3 cm^2/Vs.
For device integration, MoO3 was also tested as the active material in a charge-trapping device. Where the centrifuged and spin coated MoO3 layer where sandwiched between two layers of aluminium oxide deposited via atomic layer deposition a 3nm Al3O3 tunnel oxide layer grown on the highly doped silicon substrate and 7nm blocking oxide capping the MoO3 layer. Testing for charge trapping effects was conducted via AFM conductive tip by current mapping and sweeping to extract the device's electrical characteristics. This research highlights the potential of MoO3 in advance charge-trapping memory device fabrication.

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