CVD Growth of Monolayer MoS 2 on Sapphire Substrates by using MoO 3 Thin Films as a Precursor for Co-Evaporation
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.657
CVD Growth of Monolayer MoS2 on Sapphire Substrates by using MoO3 Thin Films as a Precursor for Co-Evaporation Sajeevi S Withanage1,2 and Saiful I Khondaker1,2,3 1
Department of Physics, University of Central Florida, Orlando, FL 32816, United States
2
NanoScience Technology Center, University of Central Florida, Orlando, FL 32816, United States
3 Department of Electrical & Computer Engineering, University of Central Florida, Orlando, FL 32816, United States
ABSTRACT
Scalable synthesis of two-dimensional molybdenum disulfide (MoS2) via chemical vapor deposition (CVD) is of considerable interests for many applications in electronics and optoelectronics. Here, we investigate the CVD growth of MoS2 single crystals on sapphire substrates by using thermally evaporated molybdenum trioxide (MoO3) thin films as molybdenum (Mo) source instead of conventionally used MoO3 powder for co-evaporation synthesis. The MoO3 thin film source provides uniform Mo vapor pressure in the growth chamber resulting in clean and reproducible MoS2 triangles without any oxide or oxysulfide species. Scanning electron microscopy, Raman spectroscopy, photoluminescence spectroscopy and atomic force microscopy characterization were performed to characterize the growth results. Very high photoluminescence (PL) response was observed at 1.85 eV which is a good implication of high optical quality of these crystals directly grown on sapphire substrate.
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INTRODUCTION Molybdenum disulphide (MoS2) is an atomically thin semiconductor with direct bandgap in single layer (SL) which shows a great potential to wide range of applications in modern 2D electronics and optoelectronics including solar cells[1], photodectors[2, 3] and light emitting devices[4]. Chemical vapor deposition (CVD) based co-evaporation of molybdenum (Mo) and sulfur (S) precursors is becoming prevalent for the synthesis of SL MoS2 since[5] conventional exfoliation methods cannot produce large scale samples for scalable device fabrication[6]. Even though molybdenum trioxide (MoO3) powder is the commonly used Mo precursor for co-evaporation synthesis, it has been noted that the control of uniform Mo vapor pressure can be very challenging resulting in a growth of oxide/oxysulfide (MoO2/MoOS2) species along with MoS2[7-9]. Recently, we found that by using MoO3 thin films as a precursor rather than MoO3 powder, it is possible to grow monolayer MoS2 on Si/SiO2 substrates with high reproducibility since the uniform evaporation rate of these thin films allow to maintain uniform Mo vapor pressure at the growth phase[7]. For certain optoelectronic applications, choice of transparent growth substrate become critical as it can avoid transfer methods that involve chemicals which can degrad
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