H-point exciton transitions in bulk MoS2

Abstract

Reflectance and photoreflectance spectrum of bulk MoS2 around its direct bandgap energy have been measured at 12 K. Apart from spectral features due to the A and B ground state exciton transitions at the K-point of the Brillouin zone, one observes additional features at nearby energies. Through lineshape analysis the character of two prominent additional features are shown to be quite different from that of A and B. By comparing with reported electronic band structure calculations, these two additional features are identified as ground state exciton transitions at the H-point of the Brillouin zone involving two spin-orbit split valance bands. The excitonic energy gap at the H-point is 1.965 eV with a valance bands splitting of 185 meV. While at the K-point, the corresponding values are 1.920 eV and 205 meV, respectively.

Pressure coefficients for direct optical transitions in MoS2, MoSe2, WS2, and WSe2 crystals and semiconductor to metal transitions

“…It is worth noting that similar spectral features have been observed for MoS 2 and WS 2 in piezoreflectance spectra343536 where the authors have attributed this signal to an excited state of A exciton transition. However recent PR studies of MoS 2 crystals suggest that this resonance is associated with a direct optical transition at H point of Brillouin zone31, see the Brillouin zone in Fig. 4.…”

Direct optical transitions at K- and H-point of Brillouin zone in bulk MoS2, MoSe2, WS2, and WSe2

“…Due to the lack of proper theoretical calculations, the authors of Ref. 15 could not predict that fact and seem to misinterpret those transitions, and in fact, the B H and B transitions should be swapped. This is clearly visible in Table I, where the calculated difference DB is negative and the experimental value is nearly identical but the sign is opposite.…”

“…However, it seems obvious that there is a high similarity in C M K points and A L H points, so they all should be considered in interpretation of the experimental spectra. Recently, Saigal and Ghosh 15 Author to whom correspondence should be addressed. Electronic mail: robert.kudrawiec@pwr.edu.pl the electronic band structure for this crystal.…”

Hidden spin-polarized bands in semiconducting 2H-MoTe2

“…On the other hand, exploring the optical properties of MoTe 2 could help to clarify the ordering of the conduction bands at K or the nature of other interband transitions. For instance, the A* feature, which is ≈ 50 meV above the A transition, has been either assigned to excited excitonic states [10,11] or direct transitions at the H k-point [12][13][14]. More recently magneto-reflectance measurements showed that such feature could be attributed to an interlayer excitonic transition [15,16].…”