Role of processing parameters in CVD grown crystalline monolayer MoSe.

The quality of as-synthesized monolayers plays a significant role in atomically thin semiconducting transition metal dichalcogenides (TMDCs) to determine the electronic and optical properties. For designing optoelectronic devices, exploring the effect of processing parameters on optical properties is a prerequisite. In this view, we present the influence of processing parameters on the lattice and quasiparticle dynamics of monolayer MoSe. The lab-built chemical vapour deposition (CVD) setup is used to synthesize monolayer MoSe flakes with varying shapes, including sharp triangle (ST), truncated triangle (TT), hexagon, and rough edge circle (REC). In particular, the features of as-synthesized monolayer MoSe flakes are examined using Raman and photoluminescence (PL) spectroscopy. Raman spectra reveal that the frequency difference between the A and E peaks is >45 cm in all the monolayer samples. PL spectroscopy also shows that the synthesized MoSe flakes are monolayer in nature with a direct band gap in the range of 1.50-1.58 eV. Furthermore, the variation in the direct band gap is analyzed using the spectral weight of quasiparticles in PL emission, where the intensity ratio {(A)/(A)} and trion binding energy are found to be ∼1.1-5.0 and ∼23.1-47.5 meV in different monolayer MoSe samples. Hence, these observations manifest that the processing parameters make a substantial contribution in tuning the vibrational and excitonic properties.