Bayramov, A.H.; Bagiyev, E.A.; Alizade, E.H.; Jalilli, J.N.; Mamedov, N.T.; Jahangirli, Z.A.; Asadullayeva, S.G.; Aliyeva, Y.N.; Cuscunà, M.; Lorenzo, D.; Esposito, M.; Balestra, G.; Simeone, D.; Tobaldi, D.M.; Abou-Ras, D.; Schorr, S.: Two-Channel Indirect-Gap Photoluminescence and Competition between the Conduction Band Valleys in Few-Layer MoS2. Nanomaterials 14 (2024), p. 96/1-12
10.3390/nano14010096
Open Access Version
Abstract:
In response to the demand in few nanometer MoS2 films on large substrate area, sulfurization of MoO3 layers deposited on SiO2/Si substrate by plasma enhanced atomic layer deposition was performed and the obtained MoS2 films were tested using X-ray diffraction, confocal Raman spectroscopy and scanning electron microscopy to ensure identity, thickness and surface morphology of the films. Spectroscopic ellipsometry and steady-state, excitation power - and temperature - dependent photoluminescence technique, supported by band structure calculations with spin – orbit coupling included were then applied to trace down the evolution of electronic energy spectrum over the photon energy range 0.07-6.5 eV upon decrease of MoS2 thickness from 30 to 5 and 3 nm. Both experimental approaches solidly verify preservation of the well known, distinctive A, B, C, and D exciton structures at and above the direct energy gap down to 3 nm film thickness or 4 MoS2 layers. Two channels of indirect emission, which involve two competting valleys of the conduction band, are observed. Both 3 and 5 nm MoS2 exhibit switching from two to one channel indirect emission with temperature decrease. The former experiences such indirect-to-indirect crossover at much higher temperature than the latter, which corroborates our band structure results.