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Abstract
Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is “high quality”, this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS2 on r-plane sapphire can yield >100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding compared to that of traditionally grown MoS2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS2, and suggest that the electronic properties of the MoS2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.
Highlights
Transition metal dichalcogenides (TMDs) exhibit promising electronic[1,2], optoelectronic[3,4,5,6] and piezoelectric[7] properties with tunable band gaps[8,9,10,11]
While the boundaries are reported to have little effect on the electronic properties[13,29], we demonstrate that misaligned MoS2 domain boundaries exhibit a dramatic enhancement (~7×) in the PL and longer excited-state lifetimes compared to boundaries between aligned domains
Aligned domain boundaries (Fig. 1(e)) exhibit PL transients that are resolution-limited, indicating that the excited state lifetimes in both regions are less than 20 ps
Summary
Transition metal dichalcogenides (TMDs) exhibit promising electronic[1,2], optoelectronic[3,4,5,6] and piezoelectric[7] properties with tunable band gaps[8,9,10,11]. While the boundaries are reported to have little effect on the electronic properties[13,29], we demonstrate that misaligned MoS2 domain boundaries exhibit a dramatic enhancement (~7×) in the PL and longer excited-state lifetimes compared to boundaries between aligned domains This is due to high density of vacancies at misaligned boundaries that leads to significant molybdenum-oxygen (Mo-O) bonding in these locations. While we achieve a global enhancement in PL by >100× with an r-plane sapphire substrate, electrical measurements of field effect transistors (FET) reveal a simultaneous 2–3× degradation in field-effect mobility, contact resistance, and sheet resistance This demonstrates that the enhancement in photonic properties and electronic properties of 2D materials are not always directly correlated, and that careful control of defects and 2D/substrate interaction is critical for realizing high quality optoelectronic 2D layers
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